The Wrist and Hand

By admin Last updated Jul 6, 2023

10 – The Wrist and Hand

Chapter 10

The Wrist and Hand

David W. Stoller

Arthur E. Li

David M. Lichtman

Gordon A. Brody

In the evaluation of both normal anatomy and pathology of the wrist and hand, magnetic resonance (MR) imaging is a standard at hand and radiology society meetings. With MR imaging, it is possible for the radiologist to accomplish accurate, noninvasive imaging of specific ligamentous injuries, rendering the vague diagnosis of “wrist sprain” obsolete. As data on the biomechanics of the carpus are collected, applications are being developed for fast imaging techniques. As techniques for dynamic MR imaging of the carpus advance, these methods may become the standard for evaluating instability. This instability can best be defined as the inability of two bones or groups of bones to maintain a normal physiologic relationship.

Status of Imaging Techniques

Standard Radiography

Standard radiographic evaluation of the wrist and hand is restricted primarily to demonstrating the osseous structures. With certain localized pathologic processes, select views, such as a scaphoid and carpal tunnel view, may provide additional information. The scaphoid fat stripe, which can be identified radial to the scaphoid, and the pronator quadratus line, which is frequently obscured by fracture, are shown on posteroanterior (PA) and lateral radiographic views, respectively. However, the usefulness of the scaphoid fat stripe in diagnosing acute scaphoid fracture has been challenged. On a lateral radiograph, the static bony relationships of the radius, lunate, and capitate can be measured in longitudinal axes.

Arthrography

Wrist arthrography has been used to evaluate the integrity of the triangular fibrocartilage (TFC) and the scapholunate and lunotriquetral interosseous ligaments.¹^,²^,³^,⁴ The three-compartment (i.e., triple injection) arthrogram, in which contrast is introduced into the radiocarpal, distal radioulnar, and midcarpal joints, was considered the standard technique.⁵^,⁶ Subsequently, single-compartment arthrograms of the radiocarpal joint have been shown to have a false-negative rate of only 2% for complete perforations and 10% for complete and partial perforations together, and no additional information was provided by selective second and third injections of the distal radioulnar and midcarpal joints.⁷

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Although arthrographic findings correlate quite well with ulnar-sided wrist pain, the technique is far less effective for radial-sided problems. Manaster et al.⁸ found that although 88% of patients with ulnar pain had lunotriquetral ligament perforations, only 26% of patients with scapholunate dissociation had scapholunate ligament perforations.⁸ Arthrography, therefore, appears to be less useful in assessing the physiologic integrity of the interosseous ligaments on the radial side of the wrist.

Wrist arthrography studies (using triple-compartment technique) demonstrate poor correlation of the locations of unidirectional or bidirectional communicating defects, as well as noncommunicating defects, with the site of wrist pain.⁹^,¹⁰ Another limitation of arthrography is related to the fact that because of the nature of the arthrography technique, it is impossible to differentiate small, pinhole perforations from those that are large and biomechanically significant. Anatomic studies have shown that degenerative perforations of both the interosseous ligaments and the TFC complex are quite common in people older than 35 years of age.¹¹^,¹² Therefore, arthrography is less diagnostically useful in these patients. Kirschenbaum et al.¹³ have also shown the common arthrographic finding of TFC and intrinsic ligament perforations in young asymptomatic adults. This apparent lack of specificity of arthrography may limit its application, especially in comparison with MR imaging, in which the morphology of the TFC and intrinsic ligaments can be evaluated directly. When used, MR arthrography involves a single-compartment radiocarpal injection of contrast. We do not use conventional arthrography unless the arthrogram is part of an MR imaging evaluation.

Computed Tomography

Computed tomography (CT) has limited but well-defined applications in the wrist. It is primarily used to evaluate occult or complex fractures, fracture healing, and lucent defects and to provide improved definition of osseous detail.¹⁴ Although subtle differences in closely related soft-tissue attenuation values cannot be optimally resolved with CT, it is an excellent modality for defining the location and extent of carpal bone fractures and complex intra-articular fractures of the distal radius.¹⁵^,¹⁶ Multidetector CT arthrography has also been used to visualize interosseous ligament tears.¹⁷

Magnetic Resonance Imaging

MR imaging of the wrist provides the high spatial and contrast resolution of soft-tissue and osseous components needed for evaluation of the small and complex anatomy of the wrist and hand.¹⁶^,¹⁸^,¹⁹^,²⁰^,²¹^,²²^,²³^,²⁴^,²⁵^,²⁶^,²⁷ Supporting muscles, ligaments, tendons, tendon sheaths, vessels, nerves, and marrow are demonstrated on MR images with excellent spatial resolution using the small fields of view (FOVs) and uniform signal intensity penetration. MR imaging has replaced conventional wrist arthrography in diagnosing tears involving the intercarpal ligaments and TFC complex by allowing direct correlation of abnormalities in ligamentous and fibrocartilage morphology with the clinical presentation of pain. Multiplanar images permit direct anatomic and pathologic discrimination in the axial, coronal, sagittal, and oblique planes. Sagittal MR images display bone and ligamentous anatomy in a selective “tomography-like” section, without the overlapping of carpal bones seen on lateral radiographs. This facilitates more accurate assessment of carpal instability. Fat-suppressed PD-weighted fast spin-echo (FS PD FSE) techniques have significantly improved visualization of wrist joint fluid, increasing the accuracy of routine wrist MR evaluations relative to MR arthrography.²⁸ Foo et al.²⁹ have used high-resolution spin-echo, 2D, and 3D gradient-recalled acquisitions in the steady state (GRASS), and spoiled GRASS (SPGR) images to optimize trabecular bone detail and anatomy of the wrist (Fig. 10.1).²⁹ These techniques may need to be used in conjunction with FS or intra-articular contrast to improve identification of ligament and cartilage pathology.³⁰ Local gradient coils have been used in 3D gradient-echo imaging and phase-contrast angiography of the fingers.³¹ We routinely use a dedicated eight-channel phased-array coil at 1.5 Tesla. 3T imaging of the wrist has demonstrated an improved signal-to-noise ratio, allowing for improved assessment of osseous ligamentous structures, tendons, cartilage, and nerves (Fig. 10.2). The increased chemical shift artifact observed at 3T can be adequately addressed by increasing the receiver bandwidth. The signal-to-noise ratio will, however, decrease as bandwidth is increased. This is not an issue when using routine receiver bandwidths of 25 to 41 kH.

FIGURE 10.1 ● A 3D fast spoiled GRASS (FSPGR) with intra-articular contrast injected into the radiocarpal compartment. The torn lunotriquetral ligament (straight arrow) allows extension of contrast into the midcarpal compartment and the torn radial attachment of the TFC (curved arrow) directs contrast into the distal radioulnar joint. Note the superior trabecular bone detail on this image (coronal image; TR, 40.4 msec; TE, 14.5 msec; FOV, 4 cm; slice thickness, 2.0 mm; matrix, 512 × 256; flip angle, 30°).

FIGURE 10.2 ● Optimized signal-to-noise in routine wrist imaging using a four-channel phased-array wrist coil on a 3T imager. (A) Coronal PD FSE image. (B) Coronal FS PD FSE image. (C) Axial PD FSE image.

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MR imaging is used for the evaluation of ligamentous pathology, trauma (e.g., fracture), avascular necrosis (AVN), and Kienböck's disease, as well as for abnormalities of the TFC and carpal tunnel. In addition, the status of synovium, articular cartilage, and cortical and subchondral bone response in arthritis can be assessed and categorized. Ultra-high-frequency sonographic transducers may be useful for ultrasound assessment of the dynamic function of the superficial tendons of the wrist and hand and thus complement MR studies.³²

Imaging Protocols for the Wrist and Hand

The wrist and hand are imaged using a dedicated circumferential design phased-array coil to optimize the signal-to-noise ratio and to obtain high-resolution images. Signal-to-noise and contrast-to-noise are improved when high-field-strength (3T) magnets are used, allowing better visualization at the TFC complex, intercarpal ligaments, and cartilage. With this

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coil design, the patient's arm may be positioned at his or her side. Anatomic symmetry of both extremities can be demonstrated in the same FOV by placing both hands in a large-diameter coil. When high-spatial-resolution images requiring smaller FOVs are necessary for the opposite wrist or hand, separate acquisitions can be performed in the area of suspected pathology and a comparison of normal and abnormal anatomy can be made. Proper positioning requires alignment of the long axis of the distal radius and central metacarpal axis with the wrist in neutral position. Oblique prescriptions are not required to produce orthogonal images with this colinear alignment of the distal radius and carpus. Radial or ulnar deviation and dorsal or volar angulation should be avoided to maintain consistent alignment of the carpus. The wrist is usually positioned in pronation, with the fingers held in extension. The position of the wrist may change relative to the design of the surface coil used. When the wrist is studied in the thumbs-up position, coronal images are obtained by prescribing a sagittal plane acquisition. In this case, oblique imaging may be required to produce orthogonal plane images through the plane of the TFC and intrinsic ligaments of the wrist.

Some typical protocols include the following:

T1- and PD-weighted images are obtained in the axial, coronal, and sagittal planes. Coronal images are acquired with 2- to 2.5-mm sections, using a 6-cm FOV and a 512 × 256 or 256 × 256 matrix.
Pathology of the TFC and intrinsic ligaments is displayed on FS PD FSE coronal images, which create an arthrography-like effect by displaying the hyperintensity of fluid in contrast to the lower signal intensity of ligaments and fibrocartilage. The sequence may also be used in the axial and sagittal planes.
FS PD FSE sequences use a repetition time (TR) of 3,000 msec, an echo time (TE) between 40 and 60 msec, an 8-cm FOV, a 2- to 3-mm slice thickness, and a 256 × 256 matrix interpolated to 512. Higher matrix and TE values and lower echo train lengths produce images with less blurring.
T2*-weighted coronal images also produce excellent contrast between ligaments (the intercarpal ligaments and the TFC complex) and fluid. In fact, intrasubstance TFC degeneration is best demonstrated using T2* gradient-echo techniques, even though the intrinsic ligaments are better visualized on FS PD FSE images.
3D SPGR techniques are used to display detailed anatomy of the TFC complex and intrinsic ligaments. Using these sequences, it is possible to achieve higher-resolution MR images with a FOV between 4 and 6 cm and a lower receiver band, ± 8 kHz. Pixel resolution at a 4-cm FOV and 256 × 256 matrix is approximately 100 μm, which allows visualization of trabecular bone detail as well. FS is recommended, however, to increase the conspicuity of fluid in abnormal or injured articular cartilage.

An axial STIR or FS PD FSE sequence demonstrates tenosynovitis, ganglions, carpal tunnel syndrome and related changes in the median nerve, and neoplasms. The distinct dorsal, membranous, and volar components of the scapholunate ligament are separated on axial images through the proximal carpal row. The flexor digitorum superficialis and profundus tendons can be differentiated on gradient-echo axial images through the phalanges.

Sagittal images display the static alignment of the carpal bones, which is important in assessing the capitolunate angle

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and tilting of the lunate or the degree of scaphoid flexion or extension. The anteroposterior location of TFC tears is determined on FS PD FSE sagittal images. Fluid in the dorsal or volar ligaments of the capsule is also shown in this plane.

FIGURE 10.3 ● Identification of the dorsal fibers of the scapholunate and lunotriquetral ligaments on a coronal T1-weighted arthrogram. Although MR arthrography is frequently performed with FS, this decreases signal-to-noise. Routine FS PD FSE sequences are still used when performing MR arthrography, usually in the coronal and axial planes, to evaluate muscle and tendon pathology, chondral abnormalities, subchondral marrow edema, and noncommunicating ganglions. Postarthrogram sequences limited to FS T1-weighted sequences alone are inadequate for comprehensive diagnostic assessment.

Administration of intravenous gadolinium DTPA produces enhancement of pannus tissue and subchondral hyperemia in inflammatory arthritides. Scaphoid and lunate vascularity is studied using STIR, FS PD FSE coronal, or FS T1-weighted intravenous gadolinium-enhanced sequences. Scapholunate ligament complex visualization may also be improved with indirect MR arthrography.³³

MR arthrography with intra-articular administration of an MR contrast agent or intra-articular saline improves the accuracy of detection of ligamentous disruptions, including flap tears and intercarpal fluid communications (Fig. 10.3).³⁴ MR identification of small perforations of the TFC and intercarpal ligaments, with characterization of ligament morphology, provides more specific information than simply documenting contrast extension between the radiocarpal and midcarpal joints or radiocarpal and distal radioulnar joint, as provided by conventional arthrography.

Coupled 7.5-cm (3-inch) circular surface coils positioned in a kinematic wrist device have been used with gradient-echo protocols to track distal and carpal row motion with radial and ulnar deviation of the wrist. This information is displayed in a cine loop format and can be recorded on video or photographed.

Dorsiflexion and plantarflexion motions are best studied in the sagittal plane and require either a greater degree of freedom from the surface coil or pivoting of the coil to accommodate the increased range of motion. It is important to incorporate image quality considerations, however, when designing a surface coil with an increased diameter or anatomic coverage. Separate axial imaging sequences in positions of pronation and supination may be useful in the evaluation of subluxation patterns in the distal radioulnar joint.

Related Muscles of the Wrist and Hand

The related muscles of the wrist include the superficial and deep groups of the volar forearm muscles and superficial and deep groups of dorsal forearm muscles.

The superficial group of volar muscles includes the flexor carpi radialis (Fig. 10.4), the palmaris longus (Fig. 10.5), the flexor carpi ulnaris (Fig. 10.6), and the flexor digitorum superficialis (Fig. 10.7). The pronator teres is discussed in Chapter 9 on the elbow. The deep group of volar muscles includes the flexor digitorum profundus (Fig. 10.8), the flexor pollicis longus (Fig. 10.9), and the pronator quadratus (Fig. 10.10).

The superficial muscles of the dorsal aspect of the forearm include the extensor carpi radialis longus (Fig. 10.11), the extensor carpi radialis brevis (Fig. 10.12), the extensor digitorum (Fig. 10.13), the extensor digiti minimi (Fig. 10.14), and the extensor carpi ulnaris (Fig. 10.15). The brachioradialis and anconeus are discussed in Chapter 9 on the elbow. The deep group of dorsal muscles includes the abductor pollicis longus (Fig. 10.16), the extensor pollicis brevis (Fig. 10.17), the extensor pollicis longus (Fig. 10.18), and the extensor indicis (Fig. 10.19).

FIGURE 10.4 ● FLEXOR CARPI RADIALIS The flexor carpi radialis lies radial to the palmaris longus and ulnar to the pronator teres throughout its course. It contributes to flexion and abduction of the wrist. Distal flexor carpi radialis tendon rupture, usually occurring after a fall on the outstretched hand, can clinically mimic a scaphoid fracture.

FIGURE 10.5 ● PALMARIS LONGUS The palmaris longus is present in approximately 85% of the population and functions to flex the wrist and tighten the palmar aponeurosis. It does not have a tendon sheath but has a paratenon.

FIGURE 10.6 ● FLEXOR CARPI ULNARIS The flexor carpi ulnaris flexes and adducts the hand. It is an important dynamic stabilizer of the pisotriquetral joint and contributes superficial fibers to the pisohamate ligament. Since it lies superficial and just medial to the ulnar nerve, it serves as a marker when ulnar nerve block is performed.

FIGURE 10.7 ● FLEXOR DIGITORUM SUPERFICIALIS The flexor digitorum superficialis tendons flex the middle phalanges of each finger and, using the pulley system as a fulcrum, contribute to flexion of the fingers at the metacarpophalangeal joint. The deep fibers of the flexor digitorum superficialis origin are closely apposed with the anterior bundle of the ulnar collateral ligament at the elbow, which is why edema and hemorrhage in the flexor digitorum superficialis are commonly seen in the setting of ulnar collateral ligament tears. In the forearm, the median nerve lies just deep to the arch of the flexor digitorum superficialis muscle, and this is an area of potential nerve compression. The flexor digitorum superficialis divides into four musculotendinous units in the distal forearm, and the tendons travel though the carpal tunnel before dividing again at the level of the proximal phalanges.

FIGURE 10.8 ● FLEXOR DIGITORUM PROFUNDUS The flexor digitorum profundus tendons flex the distal phalanges at the distal interphalangeal joints and assist in flexion of the wrist and proximal phalanges. The flexor digitorum profundus divides into four musculotendinous units in the distal forearm, and the tendons travel though the carpal tunnel deep to the flexor digitorum superficialis tendons. Distal avulsions of a flexor digitorum profundus tendon, or jersey finger, can occur when an athlete gets a finger caught in an opposing player's jersey.

FIGURE 10.9 ● FLEXOR POLLICIS LONGUS The flexor pollicis longus flexes the thumb. Compression of the anterior interosseous nerve can lead to denervation of the flexor pollicis longus muscle, which may be isolated or concomitant with flexor digitorum profundus and pronator quadratus denervation.

FIGURE 10.10 ● PRONATOR QUADRATUS The pronator quadratus acts synergistically with the pronator teres to pronate the forearm. Denervation changes can be seen with anterior interosseous nerve compression.

FIGURE 10.11 ● EXTENSOR CARPI RADIALIS LONGUS The extensor carpi radialis longus extends and abducts the wrist. If extensor carpi ulnaris function is lost due to posterior interosseus nerve palsy, the extensor carpi radialis causes radial deviation because normally the attachment of the extensor carpi ulnaris to the ulnar aspect of the fifth metacarpal functions to neutralize the abduction movement applied by the extensor carpi radialis longus.

FIGURE 10.12 ● EXTENSOR CARPI RADIALIS BREVIS The extensor carpi radialis brevis provides neutral extension of the wrist. Distal ruptures of the extensor carpi radialis brevis significantly affect wrist extension.

FIGURE 10.13 ● EXTENSOR DIGITORUM The extensor digitorum extends the medial four digits at the metacarpophalangeal joints and contributes to wrist extension. The extensor digitorum tendons are connected at the level of the metacarpal bones by fibrous bands called juncturae tendinum. Boutonnière deformity results from disruption of the central slip component of the extensor tendon at its insertion into the middle phalanx.

FIGURE 10.14 ● EXTENSOR DIGITI MINIMI The extensor digiti minimi extends the proximal phalanx of the little finger at the metacarpophalangeal joint and contributes to wrist extension. Because the extensor digiti minimi tendon lies just superficial to the radioulnar articulation, it is often the first tendon to be involved in rheumatoid arthritis.

FIGURE 10.15 ● EXTENSOR CARPI ULNARIS The extensor carpi ulnaris tendon extends and adducts the wrist. It is commonly affected in tendinosis and tenosynovitis as it passes through the groove on the distal ulna. Subluxation of the extensor carpi ulnaris can also occur at this location related to disruption or insufficiency of the ligament that covers the tendon in this groove. The extensor carpi ulnaris tendon subsheath is a component of the triangular fibrocartilage complex.

FIGURE 10.16 ● ABDUCTOR POLLICIS LONGUS The abductor pollicis longus abducts and extends the thumb at the carpometacarpal joint. It travels in the first extensor compartment of the wrist with the extensor pollicis brevis and may become involved with a stenosing tenosynovitis located under the extensor retinaculum at the distal radial groove. This condition, known as de Quervain's tenosynovitis, is distinguished from intersection syndrome, which is a result of friction-related repetitive trauma to the second extensor compartment tendons (at the point where the abductor pollicis longus and the extensor pollicis brevis muscle bodies cross). Intersection syndrome occurs proximal to the extensor retinaculum.

FIGURE 10.17 ● EXTENSOR POLLICIS BREVIS The extensor pollicis brevis travels with the abductor pollicis longus in the first extensor compartment and forms the lateral margin of the anatomic snuffbox. It is usually affected concomitantly with the abductor pollicis longus in de Quervain's tenosynovitis. The extensor pollicis brevis extends from the proximal phalanx of the thumb at the carpometacarpal joint.

FIGURE 10.18 ● EXTENSOR POLLICIS LONGUS The extensor pollicis longus tendon has a separate tendon sheath throughout its course. It can be injured in Colles' fractures of the distal radius and is sometimes involved in delayed injury following conservative treatment of nondisplaced fractures. This delayed injury is thought to be related to ischemia secondary to edema or hemorrhage compromising the fibro-osseous canal. The extensor pollicis longus extends the distal phalanx of the thumb at the carpometacarpal and interphalangeal joints.

FIGURE 10.19 ● EXTENSOR INDICIS The extensor indicis, the only extensor that has muscle fibers that extend to or beyond the level of the radiocarpal joint, extends the second finger and contributes to wrist extension. The extensor indicis is sometimes transferred surgically to replace a torn extensor pollicis longus tendon.

FIGURE 10.20 ● ABDUCTOR POLLICIS BREVIS The abductor pollicis brevis acts in conjunction with the opponens pollicis longus to abduct the thumb. It contracts during the early stages of thumb opposition and in the process also acts to rotate the phalanx. In longstanding carpal tunnel syndrome, the abductor pollicis brevis as well as the other thenar muscles may atrophy because they are supplied by the median nerve.

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The muscles of the hand include the abductor pollicis brevis (Fig. 10.20), the opponens pollicis (Fig. 10.21), the flexor pollicis brevis (Fig. 10.22), the adductor pollicis (Fig. 10.23), the palmaris brevis (Fig. 10.24), the abductor digiti minimi (Fig. 10.25), the flexor digiti minimi brevis (Fig. 10.26), the opponens digiti minimi (Fig. 10.27), the lumbricals (Fig. 10.28), and the dorsal (Fig. 10.29) and palmar (Fig. 10.30) interosseous muscles.

FIGURE 10.21 ● OPPONENS POLLICIS The opponens pollicis is part of the thenar eminence along with the abductor pollicis brevis and the flexor pollicis brevis. It acts to draw the first metacarpal laterally into a position that is favorable to opposition.

FIGURE 10.22 ● FLEXOR POLLICIS BREVIS The flexor pollicis brevis passes along the radial side of the tendon of the flexor pollicis longus. It has two portions, lateral and medial. The lateral portion arises from the flexor retinaculum and the medial portion arises from the trapezium. It acts to flex the thumb at the metacarpophalangeal joint.

FIGURE 10.23 ● ADDUCTOR POLLICIS The adductor pollicis has two heads that converge into a tendon that inserts, along with fibers from the adjacent flexor pollicis brevis, onto the ulnar side of the base of the first phalanx of the thumb. There is a sesamoid bone present in the tendon. In tears of the ulnar collateral ligament of the thumb (gamekeeper's thumb), the adductor pollicis aponeurosis can interpose between the torn ulnar collateral ligament and the thumb, precluding healing (Stener's lesion). Stener's lesions must be surgically corrected to prevent persistent instability of the metacarpophalangeal joint.

FIGURE 10.24 ● PALMARIS BREVIS The palmaris brevis is a thin superficial muscle that connects the flexor retinaculum to the ulnar skin. Rarely it is hyperactive, resulting in spasm.

FIGURE 10.25 ● ABDUCTOR DIGITI MINIMI The abductor digiti minimi abducts the little finger and contributes to flexion of its proximal phalanx at the metacarpophalangeal joint. In connective tissue diseases such as rheumatoid arthritis, prolonged contraction of the abductor digiti minimi can occur, resulting in ulnar deviation that requires surgical release.

FIGURE 10.26 ● FLEXOR DIGITI MINIMI The flexor digiti minimi brevis is part of the hypothenar eminence, along with the abductor digiti minimi and the opponens digiti minimi. It lies radial to the abductor digiti minimi and functions to flex the little finger at the metacarpophalangeal joint.

FIGURE 10.27 ● OPPONENS DIGITI MINIMI The opponens digiti minimi is the deep component of the hypothenar eminence. It stabilizes ulnar grip by rotating the fifth metacarpal and moves it anteriorly. In doing this, it brings the fifth finger into opposition with the thumb.

FIGURE 10.28 ● LUMBRICALS The lumbricals have no bony attachments. They originate from the tendons of the flexor digitorum profundus, and along with the interossei they merge to form part of the extensor expansion, which extends to the distal phalanx. They are important flexors of the metacarpophalangeal joints and also contribute to extension of the proximal and distal interphalangeal joints.

FIGURE 10.29 ● DORSAL INTEROSSEI The dorsal interossei occupy the intervals between the metacarpal bones. They abduct the second through fourth fingers from the axis of the middle finger and assist in flexing proximal phalanges of the second through fourth fingers at the metacarpophalangeal joints.

FIGURE 10.30 ● PALMAR INTEROSSEI The palmar interossei adduct the second, fourth, and fifth fingers relative to the axis of the middle finger. They also flex the same fingers at the metacarpophalangeal joint while extending them at the interphalangeal joints.

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MR Anatomic Atlas of the Wrist and Hand

Coronal Images

Coronal plane images (Fig. 10.31) are important in understanding the relationship between the cartilaginous and ligamentous structures of the wrist. Coronal images demonstrate the TFC and the intrinsic ligaments in the same plane:

On volar images, the flexor retinaculum is seen superficial to the flexor tendons as a transverse band.
En face, the hypointense bands of the flexor digitorum tendons are seen passing through the carpal tunnel between the hook of the hamate and the trapezium.
The intermediate-signal-intensity median nerve may also be discerned in this plane of section.
The pisohamate and pisometacarpal ligaments are shown in sections at the level of the hook of the hamate and pisiform.
The abductor pollicis longus and extensor pollicis brevis tendons border the volar radial aspect of the wrist in sections through the volar surfaces of the scaphoid and lunate.
The TFC is seen as a curvilinear bowtie band of hypointense, homogeneous signal intensity. The band extends horizontally to the base of the ulnar styloid process from the ulnar surface of the distal radius.
The meniscal homologue demonstrates intermediate signal intensity on T1- and T2*-weighted images.
The radioscaphocapitate ligament and the radiolunotriquetral ligament, also sometimes referred to as the long radiolunate ligament, are visualized volarly and extend from the radial styloid in an ulnar-distal direction. These fibers are seen as parallel bands of striations. The more ulnarly located radioscapholunate ligament is usually seen in the same plane as the radioscaphocapitate and radiolunotriquetral ligaments and is a less substantial structure compared with the other volar extrinsic carpal ligaments. The proximal portion of the radiolunotriquetral ligament is represented by obliquely directed fibers extending from the volar radius to the lunate, volar to the proximal pole of the scaphoid.
The distal radioulnar joint and compartment are separated from the radiocarpal compartment by the TFC.
The scapholunate and lunotriquetral interosseous ligaments are routinely visualized on 3-mm coronal T1- and T2*-weighted images.
The extensor carpi ulnaris tendon borders the ulnar aspect of the wrist on the same coronal sections that display the TFC and interosseous ligaments.
The radial collateral ligament may be partially visualized between the scaphoid and radial styloid.
The articular cartilage surfaces of the carpal bones demonstrate intermediate signal intensity on T1-weighted images and increase in signal intensity on T2*-weighted images.
On dorsal images through the carpus, the interosseous ligaments of the distal carpal row can be defined. Dorsally, the obliquely oriented extensor digiti minimi tendon on the ulnar side of the triquetrum and the extensor carpi radialis longus tendon are seen. Lister's tubercle, which contains fatty marrow, is situated between and separates the ulnar aspect of the extensor pollicis longus from the radial aspect of the extensor carpi radialis brevis. The dorsal interossei muscles are demonstrated between the midcarpal shafts.

Axial Images

Axial images (Fig. 10.32) define the dorsal, membranous, and volar components of the scapholunate and lunotriquetral intrinsic ligaments. The axial plane demonstrates the extensor and flexor tendons and the carpal tunnel in cross-section:

The flexor digitorum superficialis and profundus tendons are seen as tubular hypointense structures with invested synovial sheaths.
In proximal sections, the flexor pollicis longus is seen deep to the median nerve. Distally, it is flanked by the adductor pollicis medially and by the thenar muscles laterally, toward the thumb.
At the level of the distal radioulnar joint, the volar distal radioulnar ligament is identified as a thin, hypointense band, deep to the flexor digitorum profundus tendons and Parona's space. The position of the distal ulna in relation to the sigmoid notch is determined at this level.
The TFC complex is displayed on the ulnar aspect of the ulnar styloid.
The curve of the ulnolunate ligament is demonstrated at the level of the proximal lunate and distal radius, where it follows the contour of the ulnar and volar aspect of the lunate.
The palmaris longus tendon is superficial to the median nerve.
The thin hypointense flexor retinaculum spans the palmar border of the carpal tunnel. Its distal attachments to the hook of the lunate and tubercle of the trapezium are more reliably defined than the proximal attachments to the tubercles of the pisiform and scaphoid.
The separate extensor tendons of the extensor carpi ulnaris, extensor digiti minimi, extensor digitorum and indicis, extensor carpi radialis brevis, extensor pollicis longus, and extensor carpi radialis longus are displayed from the ulnar to the radial dorsal aspect of the wrist.
The lunotriquetral and scapholunate ligaments are usually demonstrated at the level of the proximal carpal row.
The arcuate ligament is seen volar to the capitate and deep to the flexor tendons.
The radial collateral ligament is closely applied to the radial surface of the scaphoid.

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The palmaris longus tendon is superficial to the median nerve and the flexor retinaculum.
The two central tendons of the superficial flexor group are located superiorly within the carpal tunnel before they fan out to their insertions on the middle phalanx.
On axial plane images, it is possible to differentiate the four separate tendons of the flexor profundus group.
The lumbrical muscle origins are seen deep to the flexor tendons on axial sections through the distal carpal tunnel and demonstrate intermediate signal intensity.
The median nerve, also of intermediate signal intensity, can be identified in the superficial radial aspect of the carpal tunnel.
On axial images through the midmetacarpals, the flexor tendons are seen anterior to the palmar interossei muscles, whereas the dorsal interossei are seen lying between the metacarpal bones.
Blood vessels display low signal intensity, except in venous structures demonstrated by even-echo rephasing or paradoxical enhancement secondary to slow flow. With gradient-echo techniques, both arterial and venous structures demonstrate hyperintensity.

FIGURE 10.31 ● Normal coronal anatomy. (A) Fatty atrophy or denervation of the thenar muscles raises the possibility of median neuritis, and in such cases the median nerve is closely examined for enlargement or increased signal. (B) Tenosynovitis of the flexor tendons with fluid in the tendon sheaths can occasionally cause enough mass effect on the median nerve to cause median neuritis. (C) The first carpometacarpal joint (the articulation between the trapezium and the base of the first metacarpal) is a common location for degenerative arthrosis, often visualized at the corner of a coronal image. (D) Fluid in the pisotriquetral recess is a common finding. In the absence of other findings such as degenerative changes at the joint, a small amount of fluid in the pisotriquetral recess is probably of no significance. (E) Fractures of the distal scaphoid extending to the articular surface should be characterized as entering the lunate fossa (the radial articulation with the lunate) or the scaphoid fossa (the radial articulation with the scaphoid). Such articular extension, particularly if depressed or displaced, can lead to significant radiocarpal degenerative disease. (F) The triscaphe joint consists of the distal pole of the scaphoid articulating with the trapezoid and trapezium and is considered the second most common site of wrist arthrosis. (G) The proximal row should normally form a continuous smooth convex curve. Any subtle offset of the triquetrum from the lunate, or the scaphoid from the lunate, is suggestive of a tear of the lunotriquetral or scapholunate ligaments. (H) The triangular fibrocartilage attachment to the radius may attach to hyaline articular cartilage, and it is important not to mistake the gray cartilage signal at the attachment for a tear, which is usually of fluid signal intensity. (I) The proximal pole of the hamate may occasionally articulate with a normal variant type II lunate facet located on the distal ulnar aspect of the lunate. When this occurs, degenerative changes are visualized at the hamate-lunate articulation in almost half of cases. (J) Small degenerative perforations in the membranous component of the scapholunate ligament are not uncommon in older patients, and in this population they may be asymptomatic and unassociated with carpal instability. (K) The TFC has insertions at the tip and at the base of the ulnar styloid. Therefore, fractures at the base of the ulnar styloid may disrupt the integrity of the TFC and potentially cause distal radial ulnar joint instability. (L) On coronal images through the dorsal wrist, the dorsal component of the scapholunate ligament may occasionally be discretely identified. The dorsal component is considered the most important of the scapholunate ligament components for maintaining carpal stability. (M) Another significant and commonly overlooked location for degenerative arthrosis is at the base of the third metacarpal, where a common protuberance, called a carpal boss, articulates with the capitate. Unusually prominent carpal bosses may become hypertrophic and articulate with a spur on the distal capitate, which can often be palpated by the patient as a tender bump just beneath the skin along the dorsal wrist. (N) Ganglion cysts can be visualized extending through the dorsal capsular ligaments on coronal images through the dorsal wrist. Common sites of origin are the scapholunate ligament, the triscaphe joint, and the third carpometacarpal joint (often associated with degenerative change at a carpal boss).

FIGURE 10.32 ● Normal axial anatomy. (A) Fractures of the hook of the hamate, commonly occult on plain films, are easily visualized on axial MR images through the hamate. (B) The flexor carpi radialis is visualized cradled by the hook of the trapezium. This is a common location for tenosynovitis and tendinosis of the flexor carpi radialis tendon. (C) The thenar muscles (abductor and flexor pollicis brevis) are visualized volar to the radial aspect of the distal carpus. Median neuritis should be suspected when selective fatty atrophy or denervation of the thenar muscles is visualized. (D) The median nerve within the carpal tunnel may display evidence of median neuritis, such as increased signal or enlargement. A mass lesion of the carpal tunnel at this level may cause mass effect within the carpal tunnel and impinge the median nerve. (E) The pisotriquetral joint is a common location for severe degenerative arthritis and synovitis, associated with significant ulnar-sided pain. (F) The extensor pollicis longus crosses obliquely dorsal to the extensor pollicis longus and brevis tendons. This is a not uncommon location for tears of the extensor pollicis longus tendon. (G) The scapholunate articulation is a common location for ganglion cysts, usually found directly dorsal to the scapholunate ligament. Even small dorsal ganglion cysts in this location can be exquisitely tender and painful. Often, a small neck of fluid signal extends from the dorsal ganglion cyst back toward the scapholunate ligament, and in certain cases a small perforation of the scapholunate ligament can be suggested. (H) The extensor pollicis brevis and abductor pollicis longus tendons are located lateral to the distal radius. Tendinosis and tenosynovitis of these tendons is known as de Quervain's stenosing tenosynovitis. (I) Not uncommonly the extensor carpi ulnaris tendon is subluxed over the ulnar styloid, particularly when the patient is supinated, with the ulnar styloid pointing dorsally. This is not necessarily an abnormal finding, particularly when the extensor carpi ulnaris tendon otherwise appears normal. (J) The triangular shape of the TFC complex is best appreciated on axial images, with the apex of the triangle attaching at the ulnar styloid and the broader base of the triangle attaching at the radius. (K) The distal radioulnar joint is examined in the axial plane to view the alignment of the radius with respect to the ulna. The ulna lies within the concave groove in the medial aspect of the radius called the sigmoid notch, and the two bones lie grossly in the same plane. Mild apparent dorsal shift of the ulna with respect to the radius is normal when the wrist is scanned in full pronation (the ulnar styloid pointing ulnar-volar). (L) When the triangular fibrocartilage is torn, or if there is a displaced fracture at the base of the ulnar styloid, the distal radial ulnar joint may become somewhat destabilized, ultimately resulting in degenerative arthrosis and synovitis. Another cause of distal radioulnar joint degenerative change is the ulnar impingement syndrome, in which a short ulna erodes the ulnar aspect of the distal radius.

Sagittal Images

The sagittal imaging plane (Fig. 10.33) is routine in wrist protocols. It is especially useful in the evaluation of static instability patterns and wrist shortening (i.e., proximal migration of the capitate) and in viewing the volar-to-dorsal aspect of the TFC. Kienböck's fracture and fracture deformity (i.e., humpback scaphoid) are seen on sagittal images, complementary to coronal or axial images:

The abductor pollicis longus and extensor pollicis brevis tendons can be seen on radial sagittal images.
The scaphoid is identified on sagittal sections through the trapezium and, more dorsally, the trapezoid.
The hypointense radioscaphocapitate ligament is represented by fibers seen along the volar aspect of the scaphoid between the volar distal radius and the distal pole of the scaphoid.
The extensor pollicis longus tendon is dorsal to the radioscaphoid articulation.
The pronator quadratus muscle extends along the volar surface of the radial metaphysis and distal diaphysis.
The low-signal-intensity tendon of the flexor carpi radialis is draped volarly over the distal pole of the scaphoid.
The long axis (i.e., vertical orientation) of the flexor pollicis longus tendon is seen at the ulnar aspect of the scaphoid.
The capitate, lunate, and radius are colinearly aligned in sagittal images through the third metacarpal axis.
The radial limb of the deltoid or arcuate ligament extends proximally from the volar aspect of the capitate to the scaphoid. In the sagittal plane, the deltoid ligament may appear to connect to the volar distal surface of the lunate.
The radiolunate ligament is located between the volar lunate surface and the distal radius at the radiolunate articulation, deep to the flexor digitorum profundus tendon.
The ulnolunate ligament is radial to the TFC.
The flexor digitorum superficialis and profundus tendons are best seen volar to the capitate and lunate. The flexor retinaculum is a thin hypointense line superficial to the flexor digitorum superficialis. The ulnar limb of the arcuate ligament is seen volar to the radial aspect of the triquetrum and the ulnar aspect of the lunate, ulnar to the plane of section through the capitate.
The fourth metacarpal, the hook of the hamate, and the triquetrum are seen in the same sagittal section at the ulnar-most aspect of the lunate or radial aspect of the ulna. The lunotriquetral interosseous ligament is also seen at this level.
The TFC complex is located between the lunate and the ulna and has a concave distal surface.
On ulnar sagittal images, the flexor carpi ulnaris extends in a volar direction to insert on the pisiform.
The pisohamate and pisometacarpal ligaments attach to the hook of the hamate and the base of the fifth metacarpal, respectively.
The intermediate-signal-intensity ulnar nerve is deep to the flexor carpi ulnaris.
The ulnar collateral ligament component of the TFC complex extends between the triquetrum and ulna, as can be seen on ulnar sagittal images out of the plane of the TFC.
The thick extensor carpi ulnaris tendon is seen as a groove in the posterior aspect of the distal ulna. In peripheral ulnar sagittal sections, it can be seen to extend dorsal to the triquetrum and insert onto the base of the fifth metacarpal.

Imaging Checklist for the Wrist and Hand

The checklist for reviewing an MR examination of the wrist begins in the coronal plane with examination of the following structures:

The intrinsic carpal ligaments, including the scapholunate and lunotriquetral ligaments
The triangular fibrocartilage, including the dorsal and volar margins
The radial and ulnar styloid (for fractures) and the scaphoid and lunate fossa of the distal radius for fractures and cartilage degeneration

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The triscaphe articulation (for degenerative changes)
The distal radioulnar articulation, radiocarpal joints, intercarpal joints, and carpometacarpal joints for evidence of arthrosis or posttraumatic change

FIGURE 10.33 ● Normal sagittal anatomy. (A) The first carpometacarpal joint, visualized at the top of the field of view on sagittal images, is a common location for degenerative arthrosis. (B) Similar to the hamate, the trapezium also has a “hook,” although it is smaller and is rarely fractured. (C) An anteriorly tipped (or “flexed”) scaphoid is a sign of carpal instability, often associated with scapholunate ligament tears or scaphoid fractures. (D) DISI is suggested when the capitate lunate angle exceeds 30°. When DISI is present, the scapholunate ligament is evaluated for associated tears. (E) Sagittal images afford another opportunity to examine the hook of the hamate for fractures. (F) Triquetral fractures usually occur when the dorsal aspect of the triquetrum is avulsed by the radiotriquetral ligament. Similar to the lateral view on plain films, sagittal images demonstrate the dorsal triquetral avulsion fracture fragment. (G) Sagittal images through the abductor pollicis longus and extensor pollicis brevis tendon afford additional opportunities to identify and characterize the findings of de Quervain's stenosing tenosynovitis. (H) Occasionally, focal prominence of tortuous veins and arteries about the wrist can mimic ganglion cysts on sagittal fluid-sensitive sequences. These vessels can be distinguished from ganglions by viewing successive images and visualizing continuity of the vascular structures. (I) Tears and sprains of the dorsal and volar extrinsic capsular ligaments are optimally visualized in the sagittal plane. (J) The longitudinal extent and length of median nerve involvement in median neuritis can be measured and characterized in the sagittal plane. (K) Near its radial attachment, the triangular fibrocartilage fans out to a broad, bowtie-shaped structure, resembling the appearance of the meniscus on sagittal images of the knee. (L) Near its ulnar attachment, the triangular fibrocartilage is visualized as a short, narrow band of hypointense cartilage that represents the convergence of the dorsal and volar radial ulnar ligaments at the apex of the triangular TFC.

FIGURE 10.34 SCAPHOLUNATE LIGAMENT.

In the axial plane, the following structures are assessed:

The intrinsic ligaments, with the axial plane allowing assessment of the separate dorsal and volar components of the scapholunate and lunotriquetral ligament
The extensor tendons, including the extensor carpi ulnaris tendon on the ulnar aspect of the wrist, and the extensor pollicis brevis and abductor pollicis longus tendon on the radial aspect of the wrist, for tendinosis, tears, or tenosynovitis
The flexor tendons and the carpal tunnel on the volar aspect of the wrist
The median nerve and ulnar artery
The dorsal and volar capsule and ligaments, for the presence of ganglion cysts or sprain of the capsule
The hook of the hamate, for fracture
The TFC
The distal radioulnar joint, for instability, thenar and hypothenar atrophy (indicative of median neuritis), or strain, and to confirm or characterize fractures

Sagittal plane images are evaluated for the following:

Abnormal carpal alignment suggesting carpal instability
Fractures of the carpal bones, including the hook of the hamate, scaphoid, and lunate
Triangulation on abnormalities of the TFC, scapholunate, and triquetrolunate ligaments
Ganglion cysts
Capsular sprain
Fractures

Coronal Plane Checklist

(1) Scapholunate Ligament (Fig. 10.34) and Lunotriquetral Ligament (Fig. 10.35)

Both the scapholunate and lunotriquetral ligaments are composed of dorsal and volar components comprising the dorsal and volar margins of the ligaments and a membranous component sandwiched between the dorsal and volar components. By viewing successive coronal images dorsal to volar, these separate components of the ligament are visualized and can be examined for tears.

Dorsal images display the transversely oriented ligamentous fibers of the dorsal component of the scapholunate ligament. The dorsal ligament fibers attach firmly to bone on both sides of the scapholunate articulation. The dorsal component is the strongest of the three scapholunate ligament components and is the most important in maintaining carpal stability. The next two or three successive images demonstrate the triangular membranous portion of the scapholunate ligament. A thin band of gray articular cartilage is often interposed between the membranous scapholunate ligament and the underlying scaphoid and lunate articulations and should not be mistaken for a tear.

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However, a fluid-filled gap interposed between the membranous scapholunate ligament and the cartilage or bones should be interpreted as a perforation or detachment. Such membranous scapholunate ligament perforations and detachments are more common with advancing age (similar to tears of the TFC central disc), and in isolation may not necessarily result in carpal instability or significant symptoms. The volar-most images demonstrate the volar scapholunate ligament, which courses obliquely and attaches to bone on either side of the ligament. Tears of the volar and radial aspects of the scapholunate ligament suspected in the coronal plane can be confirmed in the axial plane. After identifying a scapholunate ligament tear, the scapholunate interval is assessed for widening, reactive bone marrow changes on either side of the scapholunate articulation, and bony or cartilaginous avulsions at the site of tearing or detachment. In addition, in the setting of scapholunate ligament tears, associated patterns of carpal instability, such as dorsal intercalated segment instability (DISI) pattern, can be identified on corresponding sagittal images.

FIGURE 10.35 LUNOTRIQUETRAL LIGAMENT.

Similar to the scapholunate ligament, the lunotriquetral ligament also has a dorsal, membranous, and volar component. Compared to the scapholunate ligament, the lunotriquetral ligament may be more difficult to visualize on MR examination. The membranous lunotriquetral ligament is delta-shaped and also often has cartilage interposed between the ligament and bone. The radial and volar components attach directly to bone. Occasionally the only sign of lunotriquetral ligament injury is a subtle step-off in the alignment of the lunate and triquetrum on coronal images. Lunotriquetral ligament tears are not uncommonly seen as part of the spectrum of ulnar abutment syndrome.

(2) Triangular Fibrocartilage (Fig. 10.36)

The TFC is triangular in cross-section, so that the broadest portion of the triangle attaches to the radius and the apex of the triangle converges on the ulnar styloid. In a neutrally positioned wrist, the most dorsal image through the TFC demonstrates the dorsal radial ulnar ligament at the radial attachment. The next two or three successive images in a volar direction demonstrate the central disc and the ulnar attachments of the TFC. The most volar image displays the volar radial ulnar ligament at its radial attachment. The central disc of the TFC is made of fibrocartilage (like the menisci) and appears as an eccentric bowtie on coronal images, wider along the ulnar side, narrower near the radial attachment. When the wrist is imaged in pronation or supination, the orientation of the ulnar styloid is changed with respect to the radius, changing how the TFC appears on coronal slices.

TFC tears can either be degenerative (common in older populations and often asymptomatic) or posttraumatic (more often clinically significant and more commonly seen in younger patients). Degenerative tears and perforations most commonly are seen just proximal to the radial attachment of the TFC. According to the Palmer classification, posttraumatic tears can occur in the central portion of the TFC proximal to the radius or, less commonly, at the radial attachment or ulnar styloid attachment. The central disc attachment to the radius may attach to hyaline articular cartilage, and it is important not to mistake the gray cartilage signal at the attachment for a tear, which is usually of fluid signal intensity. The ulnar side of the TFC usually attaches to the ulna via two ligamentous fascicles, one to the base of the ulnar styloid and the other to the tip. These ulnar-sided attachments are less frequently torn. The ulnar-sided attachments, however, can be disrupted with ulnar styloid fractures that occur at the base of the ulnar styloid, leading to instability. Therefore, it is important to distinguish ulnar styloid tip fractures from fractures that occur at the base. Tears of the central disc are most easily seen on coronal images.

(3) Distal Radius and Ulna (Fig. 10.37)

Fractures of the distal radius and ulna are evaluated on coronal images. In particular, extension of radial fractures into the articular surface of the radius are characterized. The distal radius articular surfaces are divided into two concave cartilage-covered surfaces known as the lunate fossa (which is medial and articulates with the lunate) and the scaphoid fossa (which is lateral and articulates with the scaphoid). Fractures through the lunate fossa can further be characterized on sagittal images as extending through the dorsal or palmar medial

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aspect of the lunate fossa. The distal lateral tip of the radius is known as the radial styloid. Fractures through the radial styloid may extend into the scaphoid fossa. Fractures through the lunate and scaphoid fossae can lead to subsequent radiocarpal degenerative arthrosis. Fractures of the ulnar styloid are characterized as occurring either at the distal ulnar styloid or at the base of the ulnar styloid. Fractures that occur at the base of the ulnar styloid can destabilize the ulnar attachments of the TFC, leading to subsequent distal radial ulnar joint instability.

FIGURE 10.36 Triangular Fibrocartilage.

(4) Radiocarpal Joints (Fig. 10.38)

The cartilage surfaces and subchondral bone of the distal radius and the proximal carpal row are evaluated in the coronal plane. Radioscaphoid arthrosis is the most common site of degenerative arthrosis in the wrist. In its earliest stages, radioscaphoid arthrosis begins at the distal radial styloid-scaphoid articulation (stage I scapholunate advanced collapse [SLAC]) and progresses to involve the entire radioscaphoid articulation (stage IIA SLAC). Subchondral edema and sclerosis and overlying cartilage fissuring, fibrillation, or full-thickness erosion is also characterized on coronal images.

Ulnocarpal (ulnolunate) abutment syndrome is most commonly visualized as chondromalacia and subchondral edema or sclerosis at the proximal ulnar aspect of the lunate, opposite the TFC, and is classically associated with TFC tears, lunotriquetral ligament tears, and ulnar positive variance. Ulnar positive variance, however, is not required for the diagnosis. Also, proximal triquetral chondromalacia and subchondral changes can be seen with ulnar styloid impaction (a distinct entity from ulnocarpal abutment syndrome), in which a prominently enlarged

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ulnar styloid can chronically impact the proximal triquetrum.

FIGURE 10.37 DISTAL RADIUS AND ULNA.

FIGURE 10.38 RADIOCARPAL JOINT.

(5) Intercarpal Joints including the Triscaphe Joint (Fig. 10.39)

The triscaphe joint is examined in the coronal plane. The triscaphe joint consists of the distal pole of the scaphoid articulating with the trapezoid and trapezium and is considered the second most common site of wrist arthrosis. Triscaphe arthrosis is commonly seen concurrently with radioscaphoid arthrosis. Other intercarpal articulations examined in the coronal plane for arthrosis include the scaphocapitate, hamate-lunate, and trapeziotrapezoidal articulations. Particular attention should be paid to the hamate-lunate articulation in the presence of a medial lunate facet, as in one cadaveric study 44% of specimens with medial lunate facets demonstrated arthrosis at this articulation.

(6) Carpometacarpal Joints (Fig. 10.40)

The carpometacarpal articulations are examined for the presence of arthrosis, which most commonly occurs at the first carpal-metacarpal joint. A prominent protuberance (or ossicle) at the base of the dorsal third or second metacarpal (called a carpal boss) can also be identified in some patients on coronal images, and evidence of carpal boss impingement (bone marrow edema, degenerative arthrosis, adjacent ganglion cysts) may also be identified. An ossicle at the base of the dorsal third or second metacarpal is called an os styloideus and also can be associated with degenerative changes at the carpometacarpal joint.

(7) Distal Radioulnar Joint (Fig. 10.41)

The articular surface of the distal ulna articulates with the sigmoid notch of the distal radius. The coronal plane is optimal for evaluating arthrosis (as evidenced by spurring, reactive edema, or erosions at the joint), as well as associated distal radioulnar joint effusions and synovitis. The ulnar impingement syndrome, in which there is a short ulna that impacts and erodes the ulnar aspect of the radius, is also well displayed on coronal plane images. This is a distinct entity from the ulnocarpal (ulnolunate) abutment syndrome, which involves ulnar-carpal impaction. In addition, ulnar minus or positive variance is best assessed in the coronal plane, although pronation and supination can change the alignment of the ulnar articular surface with the radius, leading to false-positive diagnoses. Such ulnar variance can change the normal balance of load transfer across the wrist (normally 82% radial and 18% ulnar). Ulnar positive variance is thought to be associated with ulnocarpal

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(ulnolunate) impaction syndrome, whereas ulnar negative variance may be associated with Kienböck's disease of the lunate. With distal radioulnar joint instability, the ulna is dorsally or volarly subluxed with respect to the radius, usually due to severe TFC complex tears.

FIGURE 10.39 CARPAL JOINTS.

FIGURE 10.40 CARPOMETACARPAL JOINTS.

(8) Osseous Integrity and Fractures (Fig. 10.42)

Other osseous pathology affecting the distal radius and ulna and carpus, such as fractures, tumors, and AVN, are also evaluated in the coronal plane. Kienböck's disease of the lunate is associated with ulnar negative variance. AVN commonly affects the proximal scaphoid as a result of fracture, or less commonly in the absence of fracture (Preiser's disease).

Axial Plane Checklist

(1) Scapholunate and Lunotriquetral Ligaments (Fig. 10.43)

Axial images through the scapholunate and lunotriquetral ligaments may also aid in further characterizing the extent of tears through the dorsal, membranous, and/or volar aspects of the ligament.

(2) Extensor Tendons (Fig. 10.44)

There are six extensor compartments containing the dorsal extensor tendons. In the axial plane these tendons are displayed in cross-section, which makes axial plane imaging ideal for the demonstration of tendinosis, tears, and tenosynovitis (fluid and synovitis in the tendon sheath):

Compartment 1 lies along the lateral aspect of the radius and contains the extensor pollicis brevis and the abductor pollicis longus.
Compartment 2 contains the extensor carpi radialis brevis and longus.
Compartment 3 contains the extensor pollicis longus.
Compartment 4 contains the extensor digitorum tendons.
Compartment 5 contains the extensor digiti minimi.
Compartment 6 contains the extensor carpi ulnaris, which runs within the groove formed by the ulnar styloid.

The most common compartments to be associated with abnormalities are compartments 1, 2, 3, and 6. Tenosynovitis and tendinosis of the first extensor compartment, known as de Quervain's disease, usually occurs secondary to chronic repetitive motion injury. Tenosynovitis of the second extensor compartment (called intersection syndrome) occurs along the dorsal

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radial aspect of the distal forearm (proximal to the wrist), where the first compartment muscles cross over the second extensor compartment tendons. Tendinosis and tearing of the extensor carpi ulnaris (in compartment 6) is also common and presents as dorsal ulnar-sided pain. The extensor pollicis longus (in compartment 3) can also occasionally tear. The distally retracted, thickened, and frayed end of the torn extensor pollicis longus is often visualized at the level of the proximal carpal row, where the extensor pollicis longus tendon crosses dorsal to the extensor carpi radialis brevis and longus tendons.

FIGURE 10.41 DISTAL RADIOULNAR JOINT.

FIGURE 10.42 SCAPHOID AND LUNATE.

(3) Flexor Tendons (Fig. 10.45)

The flexor tendons are also evaluated on axial images for the presence of tenosynovitis, tendinosis, or tearing. On the ulnar aspect of the wrist, the flexor carpi ulnaris runs outside the flexor retinaculum and is separate from the carpal tunnel. The flexor digitorum superficialis and profundus tendons lie within the flexor retinaculum. The flexor pollicis longus tendon is the most radially located tendon within the carpal tunnel. The flexor carpi radialis tendon lies radial and volar to the carpal tunnel in its own fibroosseous tunnel and commonly demonstrates tenosynovitis at the level where the tendon abuts the medial aspect of the hook of the trapezium, a common area of tendon impingement.

(4) Median Nerve (Carpal Tunnel) and Ulnar Nerve (Guyon's Canal) (Fig. 10.46)

The median nerve is imaged in cross-section on axial images and normally appears intermediate in signal, with an oval shape at the distal radius and an elliptical shape at the pisiform. The axial plane is well suited to assessment of median neuritis, including signs such as swelling and enlargement at the level of the pisiform and flattening at the level of the hamate. Secondary signs of median neuritis seen on axial images include palmar bowing of the flexor retinaculum and increased signal in the thenar muscles due to denervation. Although most often median neuritis is idiopathic, underlying causes are occasionally demonstrated, such as median nerve tumors, trauma, ganglion cysts, or tenosynovitis of the flexor tendon sheaths.

The ulnar nerve is also imaged in cross-section on axial images. The ulnar nerve is located in the volar medial aspect of the wrist within Guyon's canal, which runs just palmar and lateral to the pisiform and hook of the hamate. Ulnar neuritis from pathology in Guyon's canal is much less common than median neuritis.

(5) Carpus (Including the Hook of Hamate) (Fig. 10.47)

Successive axial images of the carpal bones allow detection and characterization of fractures, contusions, and other osseous

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abnormalities. In particular, close attention should be paid to the hook of the hamate in the axial plane. Pisotriquetral arthrosis and synovitis are also evaluated on axial images.

FIGURE 10.43 SCAPHOLUNATE LIGAMENT.

FIGURE 10.44 EXTENSOR COMPARTMENT.

FIGURE 10.45 FLEXOR COMPARTMENT.

FIGURE 10.46 MEDIAN AND ULNAR NERVE.

FIGURE 10.47 CARPUS.

FIGURE 10.48 GANGLION CYSTS.

(6) Ganglion Cysts and Capsular Ligaments (Fig. 10.48)

Ganglion cysts are common, and although they are best detected on axial images, the sagittal and coronal planes are used for confirmation and further localization. On successive images through the wrist (preferably FS PD FSE images), the dorsal and volar capsular and ligamentous surfaces should be carefully inspected for the presence of fluid-signal ganglion cysts. Ganglions can be as small as 2 to 3 mm or can reach up to several centimeters in size. Ganglion cysts may protrude from nearly any wrist articulation, often with extension of a funnel-shaped neck back toward the ligament of origin. Common sites of origin are the dorsal scapholunate ligament (where even the smallest ganglions can cause symptoms by impinging the dorsal interosseous nerve), the volar radiocarpal joint, and the triscaphe joint. Volar ganglion cysts may compress the carpal tunnel, where they can contribute to median neuritis. Ganglion cysts are distinguished from free fluid in the joint space deep to the dorsal wrist capsule by looking for evidence of fluid loculation in a ganglion cyst, usually evidenced by a multilobulated, septated, and more localized appearance. In addition to causing symptoms, ganglion cysts may also be a clue to tears or perforations in the underlying ligaments from which they arise, presumably from fluid extending through a ligament perforation via a one-way valve mechanism.

The axial plane is also used in the assessment of synovitis and sprain or tears of the dorsal and volar capsular ligaments.

(7) Distal Radial Ulnar Joint (Fig. 10.49)

The distal radioulnar joint is examined in the axial plane to view the alignment of the radius with respect to the ulna. The ulna should lie within the concave groove in the medial aspect of the radius called the sigmoid notch, and the two bones lie grossly in the same plane. Mild apparent dorsal shift of the ulna with respect to the radius is normal when the wrist is scanned in full pronation, and mild volar shift of the ulna is normal in full supination. Studies show that the radius is actually moving with respect to a stationary ulna. The position of the ulnar styloid in the axial plane is used to assess the position of the wrist:

In a neutral position the ulnar styloid is located medially.
In pronation the ulnar styloid points volarly.
In supination the ulnar styloid points dorsally.

One easy way to remember this rule is that in supination, the ulnar styloid points dorsally, with the ulnar styloid groove also pointing dorsally, resembling a bowl of soup (hence, supination).

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The dorsal radioulnar ligament and palmar radioulnar ligament are the primary ligamentous stabilizers of the distal radioulnar joint and on axial plane images are seen coursing on both the dorsal and volar sides of the TFC, at the level of the base of the ulnar styloid, where the ligaments insert. Tears of the dorsal radioulnar ligament are associated with volar subluxation of the ulna. Tears of the volar radioulnar ligament are associated with dorsal subluxation of the ulna. Distal radioulnar joint instability is suggested when the ulnar head is abnormally subluxed or dislocated with respect to the radius, beyond the normal range of motion allowed for pronation and supination. In addition to ligamentous injury, osseous injuries such as fractures at the base of the ulnar styloid also may lead to distal radioulnar joint instability.

FIGURE 10.49 DISTAL RADIOULNAR JOINT.

FIGURE 10.50 CARPUS.

Sagittal Plane Checklist

(1) Hook of Hamate, Scaphoid, and Lunate (Fig. 10.50)

The length of the hook of the hamate is also visualized in the sagittal plane, and fractures of the hook of the hamate are also evaluated in the sagittal plane. Similarly, fractures and AVN of the scaphoid and lunate are also further characterized on sagittal images.

(2) Carpal Alignment (Fig. 10.51)

The alignment of the lunate and capitate is evaluated on sagittal images. DISI is suggested when the capitate lunate angle

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exceeds 30°. When DISI is present, the scapholunate ligament is evaluated for associated tears. The position of the scaphoid with respect to the rest of the carpus is also assessed. An anteriorly tipped or “flexed” scaphoid is an additional sign of DISI. When the lunate is tipped in a volar direction, with palmar translocation of the carpus, volar intercalated segmental instability (VISI) is suggested. VISI is associated with lunotriquetral ligament tears and dorsal extrinsic ligament injuries.

FIGURE 10.51 CARPAL ALIGNMENT.

FIGURE 10.52 GANGLION CYSTS AND DORSAL CAPSULE.

(3) Ganglion Cysts and Capsular Ligaments (Fig. 10.52)

Ganglion cysts suspected on axial images are confirmed and further characterized in the sagittal plane. In addition, strain or tears of the dorsal and volar extrinsic capsular ligaments can be demonstrated.

(4) Flexor and Extensor Tendons (Fig. 10.53)

The flexor and extensor tendons and the median nerve are seen in their long axis on sagittal images. Many of the tendons are seen along their entire course through the FOV on only one or two sagittal images. However, tendons are sometimes incompletely imaged in the sagittal plane due to slice gaps.

(5) Triangular Fibrocartilage, Scapholunate, and Lunotriquetral Ligaments (Fig. 10.54)

On sagittal images, the ulnar aspect of the TFC is the apex of the triangle and appears as a relatively thin band of fibers. On successive images toward the radius, the TFC fans out in a dorsal to volar direction. Near the radius, the normal TFC appears bowtie-shaped,

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similar to the meniscus. Tears of the TFC are visualized as defects or gaps in the substance of the TFC. Tears of the membranous portion of the TFC manifest as a gap with a diastasis between the two ends of the bow-tie. The scapholunate and lunotriquetral ligaments are harder to visualize on sagittal images. However, tears of the dorsal or volar components of these ligaments, or ganglion cysts extending through these ligaments, are occasionally seen and further characterized on sagittal images.

FIGURE 10.53 NORMAL TENDONS AND NERVES.

FIGURE 10.54 TRIANGULAR FIBROCARTILAGE AND SCAPHOLUNATE LIGAMENT.

Sample MRI Report, Wrist Injury

Clinical Information: Wrist pain, evaluate for TFC complex tear

Technique: Coronal and axial T1-weighted and FS PD FSE images and sagittal FS PD FSE images

Findings: Dissociation of the scapholunate interval is demonstrated with a diastasis of more than 4 mm (Fig. 10.55A). This is associated with disruption of all components of the scapholunate ligament (Fig. 10.55B). Superimposed mild proximal migration of the capitate with arthrosis between the lunate and capitate (Fig. 10.55C) is visualized on coronal images. There is cystic change within the distal pole of the capitate (Fig. 10.55C). Mild sclerosis of the radial styloid scapho-lunate articulation is consistent with a component of SLAC arthritis (Fig. 10.55D).

Degenerative change of the triangular fibrocartilage is shown with fraying of both proximal and distal surfaces of its radial aspect (Fig. 10.55E). Mild dorsal capsular synovitis (Fig. 10.55F) is seen. Small cystic fluid collections consistent with small ganglions communicating with the pisiform triquetral joint are seen (Fig. 10.55G). There is mild tenosynovitis of the second extensor compartment and mild tenosynovitis of the flexor carpi radialis (Fig. 10.55H).

A DISI pattern exists with dorsal tilting of the capitate on sagittal images (Fig. 10.55I).

Impression:

Scapholunate ligament diastasis with greater than 4 mm of diastasis of the scapholunate ligament. Superim-posed arthrosis of the capitolunate articulation.
Mild sclerosis of the radial styloid scapholunate articulation consistent with a component of SLAC arthritis.
Fraying of the proximal and distal aspects of the triangular fibrocartilage.
Mild degenerative change in the lunotriquetral ligament.
Synovitis and ganglion cyst in communication with the pisiform triquetral articulation.
DISI instability of the wrist with dorsal tilting of the lunate.

Functional Anatomy of the Wrist and Hand

Osseous Structures

The osseous elements of the wrist consist of the distal radius and ulna, the proximal and distal carpal rows, and the bases of

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the metacarpals. There are three major compartments of the wrist as defined by arthrographic studies:

The radiocarpal compartment
The midcarpal compartment
The distal radioulnar joint compartment

FIGURE 10.55

Distal Radioulnar Joint

On its medial side, the distal radius forms a shallow depression for articulation with the ulnar head (Fig. 10.56). The sigmoid notch acts as a seat for the rotating pole of the distal ulna and provides some bony stability to the distal radioulnar joint. The distal radioulnar joint is inclined 20° distally and ulnarly, and this angle of inclination is thought to be important in maintaining forearm rotation. The stabilizing ligaments for the joint include the TFC and the dorsal and volar capsular ligaments (Fig. 10.57). These capsular ligaments are poorly defined and cannot be visualized as distinct anatomic structures. The TFC connects the ulna and radius at their most distal edges and separates the distal radioulnar joint from the radiocarpal joint. The TFC runs from the ulnar-most edge of the lunate facet and sigmoid notch to the base of the ulnar styloid, where it inserts into a small depression in the distal ulna known as the fovea. The ulnar insertion consists of two limbs: one distal and one proximal. However, traumatic loss of the soft-tissue stabilizers of the distal radioulnar joint, primarily the TFC complex, may cause subluxation of the radius on the fixed unit of the ulna.³⁵ The distal radioulnar joint and synovial cavity are identified between the distal radius and ulna and extend across the distal ulna deep to the TFC.³⁶

Pearls and Pitfalls

Anatomy of the Wrist
The carpal bones absorb stress from the palm to the radius, change geometric shape in response to motion, and form a proximal row intercalary segment.
The extrinsic ligaments, which connect the radius or ulna to the carpal bones or the metacarpal to the carpal bones, provide gross stability.
The intrinsic ligaments include the intercarpal ligaments, which provide intermediate stability, and the interosseous ligaments, which provide for “fine-tune” stability.

Radiocarpal Joint

The radiocarpal joint is defined by the TFC and the distal radial surface proximally and the lunate, triquetrum, and scaphoid distally.

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At the site of the radiolunate articulation, the distal articular surfaces of the radius and ulna are usually at the same level (i.e., neutral ulnar variance). Alternatively, the ulna may be relatively long (positive ulnar variance), leading to an ulnar abutment syndrome, or relatively short (negative ulnar variance), as is often seen in Kienböck's disease. The distal radius forms two facets that articulate with the scaphoid and lunate of the proximal carpal row. This articulation of the proximal pole of the scaphoid in the scaphoid fossa is quite congruent, and even a small degree of malrotation of the scaphoid may cause incongruent loading of the articular cartilage and subsequent degeneration (such as that which accompanies a SLAC wrist, as described by Watson and Ryu³⁷). The lunate facet commonly becomes incongruent following distal radius fractures, especially die-punch-type fractures. The interosseous ligaments join the proximal carpal bones at their proximal edges.³⁶

FIGURE 10.56 ● (A) An anterior view of the distal ends of the radius and ulna. The bones have been separated to reveal the ulnar notch. (B) Corresponding scaphoid and lunate fossa on coronal PD FSE image. The scaphoid has five articulations: the trapezium and trapezoid distally, the radius proximally, and the capitate and lunate medially. The lunate articulates with five bones: the radius proximally, the capitate and hamate distally, the scaphoid laterally, and the triquetrum medially.

FIGURE 10.57 ● The articular surface of the distal end of the radius and the adjacent triangular cartilage are exposed by removal of the carpal bones.

FIGURE 10.58 ● Lister's tubercle (dorsal tubercle) of the distal radius on a coronal PD FSE image. Lister's tubercle functions as a pulley for the extensor pollicis longus.

Lister's tubercle, the most prominent dorsal radial ridge, separates the extensor pollicis longus tendon (ulnar side) from the extensor carpi brevis tendon (radial side) (Fig. 10.58). This is the site of formation of bone spurs and attrition ruptures in rheumatoid arthritis.

Carpus and Midcarpal Joint

The proximal carpal row consists of the scaphoid, the lunate, and the triquetrum. It is thought that with a congenital bipartite scaphoid, the proximal row should include only the proximal pole of the scaphoid. The distal pole should be thought of as a component of the distal row. The scaphoid, lunate, and triquetrum are linked by strong interosseous ligaments that work together to form a flexible socket or acetabulum that cradles the distal row. Occasionally, anatomic imperfections in this socket lead to arthritic degeneration. The lunate may have a medial facet, which measures 1 to 6 mm in diameter. This facet is present in approximately two thirds of cadaver hands studied, and 44% of these had arthritic degeneration in the proximal pole of the hamate.³⁸ Hamate arthritis is not seen unless the medial facet was present on the lunate.³⁸ The distal carpal row consists of the trapezium, the trapezius, the capitate, and the hamate (Figs. 10.59 and 10.60).

The midcarpal joint is formed between the proximal and distal carpal rows (see Fig. 10.60). The midcarpal joint cavity is located primarily between the distal aspects of the scaphoid, lunate, and triquetrum and the proximal aspect of the distal row. Proximal extension of the midcarpal joint between the scaphoid and lunate and between the lunate and triquetrum is limited by the interosseous ligaments.³⁶ Three distal extensions of the midcarpal joint are located between the four bones of the distal carpal row. The trapezium-trapezoid or trapezoid and capitate joint spaces may communicate with the second and third carpometacarpal joints. The first carpometacarpal joint does not communicate with the midcarpal joint. The separate joint space between the hamate and the fourth and fifth metacarpals may communicate with the midcarpal joint.

Ligamentous Anatomy

Much of the interest in and appreciation of the ligamentous anatomy of the wrist derives from the advent of wrist arthroscopy. Arthroscopy allows direct examination of the ligaments of the wrist and testing of their physiologic integrity.

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All arthroscopic portals are, of necessity, dorsally placed, making examination of the volar ligaments especially easy. As a result, the dorsal ligaments initially received less attention. Definition of pathologic conditions naturally followed elucidation of the ligamentous anatomy, resulting in the development of a variety of treatment procedures.³⁹

FIGURE 10.59 ● The bones of the hand. Adjacent bones, particularly in the carpus, have been slightly separated to reveal their articular surfaces.

FIGURE 10.60 ● (A) A coronal section of the hand shows the joints of the carpal region. The thumb and little finger are anterior to the plane of section. (B) Coronal FS PD FSE image demonstrating the membranous components of the scapholunate (SL) and lunotriquetral (LT) ligaments. The central disc of the TFC is identified. (C) Complete osseous lunotriquetral coalitions are fibrous, cartilaginous, or osseous. Osseous coalitions may be incomplete or complete.

The ligaments of the wrist are classified into intrinsic and extrinsic groups (Table 10.1).⁴⁰ The extrinsic ligaments extend from the radius, ulna, and metacarpals; the intrinsic ligaments originate and insert within the carpus. In general, the role of the intrinsic ligaments is to maintain the relationships among the individual carpal bones, whereas the extrinsic ligaments are important in the relationship of the carpus as a whole to the distal radius and ulna, as well as the bases of the metacarpals. The extrinsic ligaments, as well as the intrinsic ligaments, are crucial in maintaining the intercarpal relationships. Many investigators object to this classification scheme because it is possible for imbalances of the intrinsic ligaments to cause carpal instability, a condition that was formerly thought to occur only through dysfunction of the intrinsic ligaments. However, this scheme remains useful, if only as an anatomic guide.

Extrinsic Ligaments

Radiocarpal Ligaments

The volar extrinsic ligaments (Fig. 10.61) are the most constant and the strongest of the extrinsic ligaments. Several mechanically important ligaments originate from the region of the radial styloid and distal radius, including the radial collateral and palmar radiocarpal ligaments. The latter consists of the radioscaphocapitate ligament, the radiolunotriquetral ligament (also sometimes referred to as the long radiolunate ligament), the radioscapholunate ligament, and the short radiolunate ligament.⁴¹

By virtue of their orientation and mechanical properties, the radiocarpal ligaments maintain the carpus within its radial articulation. Loss of these ligaments allows the carpus to move down the inclined plane of the distal radius and undergo ulnar translation. This condition is not uncommon in rheumatoid arthritis, in which synovitic degeneration of these soft-tissue supporting structures occurs. With ulnar translation, the distance between the radial styloid and the scaphoid increases and the scaphoid and lunate are displaced from their articular fossae. The lunate comes to rest where it articulates with the distal ulna, and the scaphoid becomes perched on the ridge between its own articulation and the lunate fossa. This incongruent loading leads to degeneration of the cartilaginous surfaces and ulnolunate impingement. Overexuberant surgical resection of the radial styloid can destroy the origin of these ligaments and may cause this type of instability. Distal ulna resection (the Darrach procedure) in the rheumatoid wrist may also lead to ulnar translation of the carpus with the loss of the ulnar buttress.

Radial Collateral Ligament

Although the radial collateral ligament is not a true collateral ligament (because ulnar and radial deviation are normal motion arcs in the wrist, and, by definition, a collateral ligament resists only pathologic or abnormal motion), it has been shown to be mechanically significant and to play a role in the mechanism of midwaist scaphoid fractures by compressing the bone along its longitudinal axis.⁴² This ligament originates on the tip of the styloid and inserts onto the radial aspect of the scaphoid at its waist. Fibers of the radial collateral ligament also extend from the scaphoid to the trapezium, blending with the transverse carpal ligament and dorsal capsular ligament.³⁶

Radioscaphocapitate Ligament

The radioscaphocapitate ligament is a very stout ligament, readily identified through the arthroscope. It originates from the radial styloid, has a minor insertion into the radial aspect of the waist of the

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scaphoid, and also inserts on the center of the capitate.⁴³ The radioscaphocapitate ligament forms a supporting sling at the waist of the scaphoid. As the fibers cross the proximal pole of the scaphoid, there is a fold of synovium that separates them from the bone.⁴⁴ In this position, the ligament can be interposed between the fragments of a scaphoid fracture and contribute to nonunion. The radioscaphocapitate ligament, which has a striated appearance on volar coronal MR images, is located distal to the radiolunotriquetral ligament, which has a similar ulnodistal obliquity (Fig. 10.62). Sagittal images demonstrate the volar location of the radioscaphocapitate in cross-section relative to the waist of the scaphoid.

TABLE 10.1 Extrinsic and Intrinsic Ligaments of the Wrist

Radiocarpal (Radial Origin)	Ulnocarpal (TFCC ligaments)	Dorsal
EXTRINSIC LIGAMENTS
Radial collateral ligament	Dorsal radioulnar ligament	Dorsal radioscapholunotriquetral ligament
Palmar radiocarpal ligament	Volar radioulnar ligament	Scaphotriquetral ligament
Radioscaphocapitate ligament	Ulnolunate ligament
Long radiolunate ligament or radiolunotriquetral	Ulnotriquetral ligament
Short radiolunate ligament	Ulnar collateral ligament
Radioscapholunate ligament	Meniscus homologue
Radiolunate ligament or ligament of Testut
Radioscaphoid ligament or ligament of Kuenz
INTRINSIC LIGAMENTS
Scapholunate ligament
Lunotriquetral ligament
Deltoid or arcuate ligaments
Trapezium-trapezoid ligament
Trapezoid-capitate ligament
Capitate-hamate ligament
TFCC, triangular fibrocartilage complex.

FIGURE 10.61 ● The radioscapholunate ligament courses between the short and long radio-lunate (radiolunotriquetral) ligaments. The fibers of the short radiolunate ligament contribute to the floor of the radiolunate space. (From Stoller DW. MRI, arthroscopy, and surgical anatomy of the joints. Philadelphia: Lippincott.)

Radiolunotriquetral Ligament or Long Radiolu-nate Ligament

Progressing ulnarly, the radiolunotriquetral ligament (also referred to as the long radiolunate ligament) is the next ligament seen. It is the largest ligament of the wrist⁴³ (Fig. 10.63) and originates ulnar to the radioscaphocapitate from the volar lip of the radial styloid process. The radiolunotriquetral ligament has an oblique course attached to the volar aspects of the lunate and triquetrum (Fig. 10.64). On volar coronal MR images it displays a striated band-like appearance,

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similar to the radioscaphocapitate ligament. There is an interligamentous sulcus between the radioscaphocapitate and the radiolunotriquetral ligaments on sagittal images (Fig. 10.65). The radiolunotriquetral is a strong ligament that stabilizes the proximal carpal row on the radius and should be differentiated from the radioscapholunate ligament.

FIGURE 10.62 ● Anatomy of the radioscaphocapitate (RSC), radiolunotriquetral (RLT), and radioscapholunate (rsl) ligaments at the level of the distal volar radius (R). T, triquetrum; S, scaphoid. FS T1-weighted arthrogram after radiocarpal injection.

FIGURE 10.63 ● The long radiolunate or radiolunotriquetral (RLT) ligament. (A) The RLT ligament is divided into a radiolunate ligament and lunotriquetral component. The RLT ligament functions as a volar sling for the lunate. L, lunate; R, radius. Volar FS coronal T1-weighted arthrogram. FS axial T1-weighted arthrograms obtained at the level of the proximal (B) and distal (C) aspects of the radial styloid show the volar course of the RLT ligament (large arrows) from the radial styloid (R) inserting into the lunate (L) and blending with the volar portion of the lunotriquetral interosseus ligament. The lunate attachment of the scapholunate interosseous ligament volar fibers is deep to the lunate attachment of the RLT ligament (B). S, scaphoid; T, triquetrum; SL, scapholunate ligament.

Short Radiolunate Ligament

The short radiolunate ligament has been described by Berger and Landsmeer.⁴⁴ This ligament originates from the radius in the region of the lunate facet and inserts distally onto the volar surface of the lunate (Fig. 10.66). At its insertion, its most radial fibers merge with those of the long radiolunate ligament. It acts as a volar tether to the lunate and plays a major role in preventing the development of DISI deformities with lunate extension.

Radioscapholunate Ligament

The radioscapholunate ligament is interposed dorsally between the long radiolunate and the short radiolunate ligaments. It arises at the level of the interfacet prominence of the distal radius and inserts onto the scapholunate articulation (Fig. 10.67).⁴³ This structure was first described in detail by Testut and is often called by his name (i.e., the ligament of Testut or the ligament of Testut or Kuenz).⁴⁵ The radioscapholunate ligament has been studied extensively, and it has been shown to contain the most elastic tissue of any ligament in the wrist. It does not appear to provide any mechanical support to the carpus.

From his work on fetal wrists, Landsmeer described a vascular pedicle that supplies the radioscapholunate ligament.⁴⁶ It has since been shown that this structure is a neurovascular umbilical cord that may provide a clinically significant blood supply to the proximal pole of the scaphoid via the scapholunate interosseous ligament and a sensory or proprioceptive pathway to the scapholunate joint.⁴⁷ The radioscapholunate ligament receives its neurovascular supply from the anterior interosseous artery and nerve.

On volar coronal MR arthrographic images, the radioscapholunate ligament can be seen as a short ligament with

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a straight course or minimally convex radial border directed toward the scapholunate interval. The radioscapholunate ligament does not have the striations previously described for the radioscaphocapitate and radiolunotriquetral ligaments on coronal images. The proximal attachment of the radioscapho-lunate ligament should never be confused with the normal articular cartilage ridge that separates the scaphoid and lunate fossa of the distal radius. This articular cartilage ridge has a broad-based attachment to the distal radius.

FIGURE 10.64 ● The radiolunotriquetral or long radiolunate ligament. This ligament acts as a volar sling for the lunate. Coronal T1-weighted arthrogram.

Ulnocarpal Ligaments

The ulnar portion of the extrinsic volar ligaments of the wrist is formed by the TFC complex (Figs. 10.68 and 10.69). The TFC complex consists of the TFC (the articular disc, the dorsal and volar radioulnar ligaments), the meniscus homologue, and the ulnolunate and the ulnotriquetral ligaments (Fig. 10.70). The term TFC complex was coined to describe all of the ligamentous and cartilaginous structures that were thought to play a role in suspending the distal radius and the ulnar carpus from the distal ulna,⁴⁸ including the subsheath of the extensor carpi ulnaris tendon. Clinical and laboratory data support the role of the TFC complex in maintaining both the stability of the distal radioulnar joint and the stability of the carpus as a whole (preventing pronosupination of the carpus). The TFC complex also contributes to stability within the carpus by preventing nondissociative carpal instabilities (see discussion below on carpal instabilities).

Dorsal Ligaments

Although the palmar or volar radiocarpal ligaments have attracted a great deal of attention in the past, the biomechanics of the wrist also relies on the dorsal ligaments.

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The dorsal ligaments do not exist as discrete anatomic entities, and they vary considerably from subject to subject. Two major components can be discerned:

The first component is the dorsal radioscapholunotriquetral ligament, a thickening of the dorsal capsule that courses from the dorsal lip of the radius and inserts on the dorsal surfaces of the scaphoid, lunate, and triquetrum. This ligament acts as a checkrein on the proximal carpal row and prevents it from assuming a position of excessive volarflexion. Biomechanical studies have shown that in the final stage of ulnar-sided perilunate instability, it is the radioscapholunotriquetral ligament that is injured.⁴⁹ Laxity of the radioscapholunotriquetral ligament has been implicated in palmar midcarpal instability patterns in which the lunate is allowed to go into volarflexion, leading to instability.
The second major component of the dorsal ligamentous structure is the scaphotriquetral (or triquetroscaphoid) ligament. This is a transversely oriented thickening of the dorsal capsular fibers that runs from the scaphoid to the triquetrum.

FIGURE 10.65 ● The interligamentous sulcus between the radioscaphocapitate (RSC) and radiolunotriquetral ligaments is seen on an FS sagittal T1-weighted arthrogram at the level of the scaphoid (S). The volar aspect of the wrist is labeled. The radio-lunotriquetral ligament is proximal to the RSC ligament.

FIGURE 10.66 ● The short radiolunate ligament (SRL). (A) The SRL (arrows) can be seen extending volarly to the lunate fossa of the distal radius to its insertion on the radial volar aspect of the lunate. S, scaphoid. FS T1-weighted coronal arthrogram. (B) The SRL is identified on an FS T1-weighted sagittal image at the level of the capitate (C) and lunate (L).

Using multiplanar reconstructions with 3DFT MR imaging, Smith⁵⁰^,⁵¹ has demonstrated and described the dorsal carpal ligaments of the wrist. The radiotriquetral ligament can be seen to consist of a single band that arises from the distal radius, adjacent to Lister's tubercle. The dorsal intercarpal ligament is seen either as a broad fused band (a branched structure) with separate triquetroscaphoid and triquetrotrapezoid fascicles, or as completely separate triquetroscaphoid and triquetrotrapezoid fascicles (Figs. 10.71 and 10.72).

Intrinsic Interosseous Ligaments

Scapholunate and Lunotriquetral Ligaments

The interosseous ligaments are of paramount importance in maintaining the biomechanical relationship among the carpal bones, especially those of the proximal row (Fig. 10.73). For the proximal carpal row to function properly, the bones must be associated or linked together, and the interosseous ligaments provide this flexible linkage. The scapholunate and lunotriquetral ligaments are comparable in strength with the anterior cruciate ligament of the knee. They connect the bones at the level of the proximal articular surface and consist of thick dorsal and volar components with thinner membranous portions in between. Most commonly, perforations occur in the thin, membranous portions and may not be mechanically significant. Specific characteristics of the scapholunate and lunotriquetral ligaments include:

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The scapholunate ligament is triangular on coronal section and is peripherally attached at the scapholunate interval. The inner apex of the triangular ligament is not attached to bone and is free within the scapholunate joint (Fig. 10.74).⁵²
The dorsal fibers of the scapholunate ligament are oriented transversely, or perpendicular to the joint, and form a thick bundle. The dorsal portion of the scapho-lunate ligament is considered to be the most important component in maintaining carpal stability.
The membranous scapholunate ligament fibers course peripherally and obliquely from the scaphoid downward to the lunate. The membranous scapholunate ligament fibers attach to both bone and articular cartilage, whereas the dorsal and volar portions of the scapholunate ligament attach directly to bone.
The volar scapholunate ligament fibers course obliquely between the volar aspects of the lunate and scaphoid.
The lunotriquetral ligament is usually visualized as a thin horseshoe-shaped structure that may appear more lax than the scapholunate ligament on MR imaging.⁴³ The lunotriquetral ligament does not extend as far distally into the lunotriquetral joint as the longer proximal distal portion of the scapholunate ligament does within the scapholunate joint.
The volar and dorsal portions of the lunotriquetral ligament attach directly to bone, whereas its midportion attaches to the hyaline articular cartilage of the lunotriquetral joint.⁴³
Smith and Snearly⁵³ have shown that on coronal MR images the lunotriquetral ligament is most commonly delta-shaped (triangular) or linear.

FIGURE 10.67 ● Anatomy of the radioscapholunate (RSL) and radioscaphocapitate (RSC) ligaments. (A) The RSL ligament represents a neurovascular structure extending from the distal radius into the scapholunate articulation. This ligament, which has also been referred to as the ligament of Testut and Kuenz, is located volar to the intrinsic scapholunate ligament. RLT, radiolunotriquetral ligament; L, lunate; R, radius. FS coronal T1-weighted arthrogram. (B) RSL (arrow) extending to the scapholunate interval between the scaphoid (S) and lunate (L). Note the relative volar location of the extrinsic RSL to the intrinsic scapholunate ligament. sl, dorsal and volar portions of the intrinsic scapholunate ligament. FS axial T1-weighted arthrogram. (C) At the level of the distal radius, the normal articular cartilage (AC) ridge between the scaphoid fossa and lunate fossa demonstrates a triangular appearance and is seen in the same plane as the intrinsic scapholunate ligament. This articular cartilage ridge should not be mistaken for a site of ligamentous attachment. Spoiled GRASS (SPGR) coronal image with a 4-cm FOV and 1-mm slice thickness.

Arcuate Ligaments

More distally, there is a set of ligaments that stabilizes the distal carpal row on the proximal row. These ligaments have been referred to as the deltoid ligaments ⁵⁴ or arcuate ligaments (Fig. 10.75)⁵⁵ and include the following:

The ulnar arcuate ligament extends from the volar surface of the lunate and triquetrum to the neck of the capitate

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and plays a role in preventing the proximal row from volarflexion (see Fig. 10.75). Progressing radially, the substance of this structure becomes quite thin in the region of the capitolunate articulation.
The radial limb (i.e., radial arcuate ligament) of this V-shaped ligament runs from the capitate to the distal pole of the scaphoid.

FIGURE 10.68 ● A coronal section of the wrist joint shows the articular surfaces and triangular cartilage.

FIGURE 10.69 ● A T2*-weighted image showing the TFC complex. Black arrows, radial attachments of TFC; white arrows and UC, ulnar collateral ligament; M, meniscus homologue; pr, prestyloid recess.

The thin tissue between the limbs of the arcuate or deltoid ligament is known as the space of Poirier. This weak area in the ligamentous floor of the carpus may function as a trap door through which the lunate or capitate may dislocate. The particular functions of these ligaments with respect to midcarpal instabilities are discussed below in the section on carpal instabilities. The proximal fibers of the radioscaphocapitate and ulnar arcuate ligament merge volar to the head of the capitate and are joined by reflected fibers distally from the TFC ligament. This creates a sling-like support for the head of the capitate and ham-ate.⁵⁶ This sling can be appreciated as a thick hypointense band extending from the triquetrum to the scaphoid on axial images.

Distal Carpal Row Interosseous Ligaments

Within the distal row, the trapezius and trapezium, trapezoid and capitate, and capitate and hamate are connected by interosseous ligaments. In contradistinction to the interosseous ligaments of the proximal row, these ligaments do not extend from the dorsal to the volar surface; and there is normally communication between the midcarpal space and carpometacarpal joints.

Tendons of the Wrist and Hand

Palm of the Hand

The flexor retinaculum and palmar aponeurosis represent thickened deep fascia of the wrist (Figs. 10.76, 10.77, and 10.78). Important anatomic structures and features include the following:

The superficial palmaris longus tendon is fused to the midline of the flexor retinaculum and expands distally into the palmar aponeurosis.
Guyon's canal, a site of potential compression of the ulnar nerve, is formed by an ulnar extension of the flexor retinaculum superficial to the ulnar nerve and artery.
The concave volar surface of the carpus and the flexor retinaculum form the anatomic boundaries of the carpal tunnel for passage of the long flexor tendons of the fingers and thumb (Fig. 10.79).
The four flexor digitorum superficialis tendons are arranged in two rows, with the tendons to the third (i.e., middle) and fourth (i.e., ring) digits superficial to the tendons for the second (i.e., index) and fifth (i.e., little) digits (Fig. 10.80). After entering their respective fibrous flexor sheaths, the tendons of the flexor digitorum superficialis divide into two halves opposite the proximal phalanx and partially decussate around the flexor digitorum profundus tendons. Distal to the site of perforation by the flexor digitorum profundus, the superficialis tendons pass deep to the flexor digitorum profundus and send slips to attach to the sides of the middle phalanx.
The tendons of the flexor digitorum profundus are arranged in the same plane and pass deep to the flexor digitorum superficialis (Fig. 10.81). The tendons of the flexor digitorum profundus attach distally to the base of the terminal phalanx and change from a deep to a superficial location at the partial decussation of the superficialis at the level of the middle phalanx (Fig. 10.82).

Dorsum of the Hand

The extensor digitorum tendons extend across the metacarpophalangeal joints and contribute to the posterior capsule of this joint, and then they broaden out onto the dorsum of the proximal phalanx (Fig. 10.83). The extensor expansion represents the joining of the extensor tendons and posterior fascia. The extensor tendons and expansion divide into a central slip, which inserts onto the base of the middle phalanx, and two lateral or marginal slips, which diverge around the central slip and then converge to insert onto the base of the distal phalanx. The interosseous (Fig. 10.84) and lumbrical tendons insert onto the dorsal extensor expansion from each of its sides and from its lateral side, respectively.

FIGURE 10.70 ● TFC complex. (A) Volar view of the ligaments of the ulnar side of the carpus. The meniscus homologue and meniscus reflection are shown. The meniscus homologue inserts onto the volar surface of the triquetrum. The meniscus homologue shares a common origin from the dorsal ulnar corner of the radius with the TFC. The TFC extends in a volar direction from the meniscus homologue to the base of the ulnar styloid. The ulnolunate component of the ulnocarpal ligament is considered to be part of or a continuation of the short radiolunate ligament. (B) In this dorsal view, the ulnar and dorsal aspect of the TFC complex is invested by a thick ligamentous layer (the meniscus reflection) with proximal attachment to the TFC complex and ulna and distal attachment to the base of the fifth metacarpal. (C, D) The dorsal views of the TFC complex show the dorsal and volar radioulnar ligaments as separate from the articular disc of the TFC. The term TFC refers to the central horizontal articular disc and adjoining volar and dorsal radioulnar ligaments. The term TFC complex refers to the TFC and any additional ulnar ligamentous structures, such as the meniscus homologue, ulnar collateral ligament, subsheath of the extensor carpi ulnaris tendon, and ulnolunate and ulnotriquetral ligaments.

FIGURE 10.71 ● Patterns of the dorsal carpal ligaments. (A) Illustration and (B) corresponding FS T1-weighted coronal image of a single radiotriquetral ligament (RT) and the triquetroscaphoid (TS) and triquetrotrapezial (TT) fascicles of the dorsal intercarpal ligament. T, triquetrum. (C) On an FS PD FSE axial image, the TS fascicle is seen dorsally between the triquetral bone and dorsal pole of the scaphoid (S). The TS fascicle (arrows) extends over the hamate (H) and capitate (C). The palmar TS ligament is also identified at this level (arrows). P, pisiform.

FIGURE 10.72 ● The extensor retinaculum and dorsal carpal ligaments. The radiotriquetral ligament (an extrinsic dorsal capsular ligament) and the dorsal intercarpal ligament (an intrinsic dorsal capsular ligament) are illustrated. The dorsal intercarpal ligament is composed of separate triquetroscaphoid and triquetrotrapezial fascicles. The radial collateral ligament and the bilaminar extensor retinaculum are also shown. The vertical septations of the extensor retinaculum define the six extensor compartments (1-6). A slip of the extensor retinaculum attaches to the dorsal triquetrum.

FIGURE 10.73 ● Anatomy of the scapholunate ligament complex on three separate coronal images. (A) Volar component. (B) Membranous component. (C) Dorsal component. (D) On a corresponding axial image all three components of the scapholunate ligament complex are demonstrated. The dorsal scapholunate ligament is horizontally oriented and is perpendicular to the joint. The fibers of the membranous portion of the scapholunate ligament course peripherally and obliquely from the scaphoid downward toward the lunate in a dorsal-to-volar direction. The volar scapholunate ligament courses obliquely from the scaphoid downward to the lunate. This arrangement of scapholunate ligament fibers biomechanically hinges the joint dorsally at the level of the dorsal transverse fibers. In forced extension, scapholunate ligament failure initiates in its volar aspect. S, scaphoid; L, lunate; v, volar component; m, membranous component; d, dorsal component. Arrows correspond to the course of each component of the scapholunate ligament.

FIGURE 10.74 ● Membranous wedge-shaped component of the scapholunate ligament with direct proximal attachment to the articular surfaces of the scaphoid and lunate. The distal apex is free without direct attachment and presents as a prominent distal protrusion into the scapholunate articulation. (A) Coronal color illustration. (B) Coronal FS PD FSE image.

FIGURE 10.75 ● The arcuate or deltoid ligament. (A) The ulnar limb (ul) and radial limb (rl) of the volar intrinsic arcuate ligament are shown in the same volar plane on a T1-weighted coronal image. Both limbs attach centrally to the capitate. (B) The arcuate ligament is shown between the capitate (C) and lunate (L) on a midsagittal FS T1-weighted arthrogram. The ulnar limb of the arcuate or deltoid ligament is the capitoscaphoid arm, and the radial limb of the arcuate ligament is the capitotriquetral arm.

FIGURE 10.76 ● The palmar aponeurosis is revealed by removing the skin and superficial fascia. The investing fascia has been removed proximal to the flexor retinaculum. R, radius.

FIGURE 10.77 ● The flexor retinaculum and its superficial relations and structures are seen entering the carpal tunnel.

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Pathology of the Wrist and Hand

Carpal Instabilities

The terms stability and instability, as used in reference to conditions affecting the carpus, must be rigidly defined:

Stability refers to the ability of two structures to maintain a normal physiologic spatial relationship under applied physiologic loading.
Similarly, two structures are said to be unstable if they cannot maintain this normal relationship under physiologic loading conditions.

Carpal instabilities represent deviations from the normal spatial relationships of the carpal bones to each other and their surrounding structures, such as the radius, the ulna, and the metacarpals. Since the wrist, like the hip, is virtually always under some load condition, this definition includes instabilities that are seen on routine radiographs as well as those seen on motion studies.

MR imaging offers the advantage of revealing associated carpal ligament disruptions when characterizing instabilities in any specified plane of section. Fixed instabilities seen on routine radiographs and coronal or sagittal MR images are often referred to as static, and those that are revealed only by provocative maneuvers in motion studies are referred to as dynamic. Kinematic MR imaging represents a series of static evaluations displayed in a cine loop without true dynamic motion.

In many cases, the difference between dynamic and static instability is a matter of the degree of pathology in the structures that maintain the spatial relationship between the bones. A static instability that is present at all times implies contracture of the soft-tissue constraints. This condition may not be amenable to surgical repair and treatment may require arthrodesis. On the other hand, a dynamic instability that is revealed only by a provocative maneuver may be due to a relatively minor ligament tear or laxity that can be repaired with a soft-tissue procedure, allowing preservation of joint motion.

FIGURE 10.78 ● Flexor retinaculum. The concave volar surface of the carpus and the flexor retinaculum form the anatomic boundaries of the carpal tunnel (for passage of the long flexor tendons of the fingers and thumb). Medially, the flexor retinaculum is attached to the pisiform and hook of the hamate and laterally to the tuberosities of the scaphoid and trapezium. (A) Coronal color illustration (volar perspective). (B) Coronal T1-weighted image at the level of the retinaculum.

FIGURE 10.79 ● (A) A transverse section through the carpus shows the carpal tunnel and its contents. (B) Axial FS PD FSE high-resolution image of the carpal tunnel.

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Stable and Unstable Equilibrium in the Wrist

The normal spatial relationships of the individual components of the wrist (e.g., carpal bones, radius, ulna, metacarpals) can be thought of as an example of a stable equilibrium condition. Definitions of stable and unstable equilibrium include:

A stable equilibrium exists when displacement of a body from its position results in a restoring force that tends to return the body to its equilibrium position. When all of the supporting constraints of the wrist are normal and intact, any load within physiologic limits may change the spatial relationship of the components, but there will be a simultaneous increase in the tension within these constraining structures that counteracts the deforming force and tends to return the components to their normal spatial relationship. Neutral, dorsiflexion, and palmarflexion motions can be used as an example of the different colinear relationships among the capitate, lunate, and radius (Figs. 10.85, 10.86, and 10.87).
Conversely, an unstable equilibrium exists when displacement of a body from its position results in a force that tends to push the body further from the equilibrium position.⁵⁷ This condition occurs in the wrist when the constraining structures are incompetent. Constraining or supporting structures about the wrist include not only the ligamentous structures discussed earlier but also the tendons that cross the joint, as well as the geometry of the carpal bones and their surrounding articular surfaces.

The tendency for the wrist to assume a condition of unstable equilibrium when the constraining structures are damaged can be seen as an extension of the normal motions of the carpal bones. To understand these motions, the wrist can be thought of as a flexible spacer interposed between the hand (i.e., metacarpals) and the distal radius/ulna. The purpose of this deformable spacer is to maintain a constant distance or space between the base of the third metacarpal and the articular surface of the radius. This theory is supported by the fact that, with radial or ulnar deviation, the carpal height index does not change from its value as measured in the neutral position.⁵⁸ The carpal height index or ratio is defined as the carpal height measured from the distal capitate surface to the proximal lunate surface, divided by the length of the third metacarpal. In normal individuals, the value is 0.54 ± 0.03. In pathologic conditions, such as SLAC wrist or rotatory subluxation of the scaphoid as seen in scapholunate dissociation, this ratio is decreased to less than 0.49.

For this ratio to remain constant with radial and ulnar deviation, there must be a change in the dimensions of the ulnar and radial borders of the flexible spacer between the metacarpals and distal radius and ulna. Since the bones of the distal carpal row are rigidly held in place by their ligamentous restraints and do not move, the normal motions of the three bones of the proximal row must account for the changes in the dimensions of the radial and ulnar borders of the wrist:

With radial deviation the radial border must shorten, and this is accomplished by rotation of the scaphoid into a flexed position.
The ulnar border is lengthened as the triquetrum slides out from beneath the hamate.

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On plain radiographs or coronal MR images in this position, the scaphoid is foreshortened and the joint space is evident between the hamate and the triquetrum; no superimposition of these bones occurs.
The lunate is linked or associated with the scaphoid and triquetrum through the interosseous ligaments, which are displayed as homogeneous hypointense structures on coronal MR images. The scapholunate ligament has a triangular morphology, whereas the lunotriquetral ligament is more linear in shape. Lunate motion is thus a reflection of this proximal carpal row linkage, as well as the compressive forces placed on it by the capitate.
At extreme radial deviation, the summation of these forces produces slight volarflexion of the lunate. Since the wrist is in a condition of stable equilibrium, the bones of the proximal carpal row return to their neutral position when the force causing radial deviation is removed. Thus, in radial deviation, a flexion torque predominates, and compression of the scaphotrapeziotrapezoid joint and proximal carpal row flexion produce a physiologic VISI pattern.
With ulnar deviation, the radial side of the flexible spacer must lengthen and the ulnar side must shorten.
The scaphoid becomes more horizontal or extended to lengthen the radial side, and the triquetrum slides beneath the hamate to shorten the ulnar side.
PA radiographs show an elongated scaphoid and superimposition of the hamate on the triquetrum.
Coronal MR images demonstrate the triquetral movement in an ulnar direction on the slope of the hamate.
Palmar movement of the triquetrum in relationship to the hamate results in a palmar position of the lunate axis, relative to the capitate.
Compression forces transmitted by the capitate produce dorsal rotation or dorsiflexion of the lunate. Associated volar shift of the lunate maintains colinear alignment of the capitate and radius.
During lunate dorsiflexion, there is elevation of the distal pole of the scaphoid (i.e., scaphoid extension). Thus, in ulnar deviation, an extension torque predominates, and interaction at the triquetrohamate helicoid slope and proximal carpal row extension produces a physiologic DISI pattern.

FIGURE 10.80 ● (A) The palmar aponeurosis, flexor retinaculum, investing fascia, and palmar vessels and nerves have been removed to reveal the tendons of the flexor digitorum superficialis in the palm. (B) Coronal T1-weighted image at the level of the flexor tendons.

Interosseous Ligament Pathology

MR imaging is a valuable tool in evaluating interosseous ligament pathology, with excellent sensitivity, specificity, and accuracy. For evaluation of the lunotriquetral ligament, 3DFT coronal images may be needed to improve the sensitivity of diagnosis. Thin-section axial images may also improve the identification

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of both scapholunate and lunotriquetral ligament pathology. MR imaging is superior to conventional arthrography, allowing identification of the size, morphology, and location of a scapholunate or lunotriquetral ligament tear. This information is important because communication across a pinhole or small perforation or deficiency of the thin membranous portion of the ligament may not be significant in the presence of grossly intact dorsal and volar ligaments. In fact, evaluations of communicating perforations in cadaver wrists have shown that 28% of cadaver wrists have degenerative perforations of the central membranous scapholunate ligament.⁵⁹ Degenerative perforations of the membranous lunotriquetral ligament can be seen in 36% of cadaver wrists. In our experience, degenerative perforations occur twice as often in the lunotriquetral ligament as in the scapholunate ligament.

FIGURE 10.81 ● Removal of the tendons of the flexor digitorum superficialis reveals the attachments of the lumbrical muscles to the tendons of the flexor digitorum profundus.

FIGURE 10.82 ● Partial cutting away of the fibrous flexor sheath of the middle finger exposes the tendons of the flexor digitorum superficialis and profundus, revealing the phalangeal attachments in the ring and little fingers.

FIGURE 10.83 ● (A) The extensor tendons are arranged into six compartments on the dorsum of the wrist. (B, C) Extensor tendon anatomy on T1-weighted coronal MR images (A is dorsal to B).

FIGURE 10.84 ● The dorsal interossei is exposed by removing the deep fascia and the tendons of the extensor digitorum.

FIGURE 10.85 ● (A) In wrist dorsiflexion, there is colinear alignment (long thin black line) of the dorsiflexed capitate and lunate (curved arrows). The deltoid or arcuate ligament (small white arrows) and the radiolunate (short radiolunate) ligament (large white arrow) are also indicated. Dorsiflexion occurs primarily at the radiocarpal joint. (B) The radioscaphocapitate ligament (small white arrows) also tightens during wrist dorsiflexion, locking any motion between the proximal and distal carpal rows and creating a sling across the waist of the scaphoid. Both the scaphoid (curved arrow) and capitate are thus dorsiflexed.

FIGURE 10.86 ● (A) With the wrist in a neutral position, there is normal colinear alignment of the capitate, lunate, and radius (black line). The normal capitolunate angle is between 0° and 30°. (B) When the scaphoid is positioned without dorsiflexion or palmarflexion, the normal scapholunate angle is between 30° and 60°.

FIGURE 10.87 ● (A) Palmarflexion occurs primarily at the midcarpal articulation. Palmar flexion of the capitate (long curved arrow) and some palmar flexion of the lunate (short curved arrow) can be seen. The arcuate or deltoid ligament (small white arrows) is more lax. Large white arrow, radiolunate articulation. (B) Flexion of the scaphoid (curved arrow) with a lax radioscaphocapitate ligament (straight arrows).

FIGURE 10.88 ● Scapholunate ligament tear without carpal instability. (A) FS T1-weighted coronal image demonstrates a vertical high-signal-intensity tear (arrow) of the lunate attachment of the scapholunate ligament. The lunotriquetral ligament is absent. (B) Corresponding FS T1-weighted sagittal image demonstrates colinear (straight line) alignment of the capitate (C) and lunate (L) with a normal capitolunate angle. There is no static instability pattern.

MR arthrography has increased the accuracy of evaluation of scapholunate and lunotriquetral ligament tears, especially in peripheral ligament avulsions where the ligament has not lost its normal morphology. These tears may be difficult to detect on routine MR gradient-echo, STIR, or FS PD FSE images unless there is a fluid interface identified between the torn ligament and corresponding osseous attachment.

Scapholunate Ligament Tear

As discussed earlier, the scapholunate ligament complex consists of both intrinsic and extrinsic ligaments. The extrinsic ligaments provide gross stability and the intrinsic ligaments provide fine-tuning for stability. The dorsal component of the scapholunate interosseous ligament is trapezoidal, the membranous component is wedge-shaped, and the volar component consists of thin slightly oblique fibers. The separate scaphotrapeziotrapezoid ligament complex provides significant volar constraint and consists of the following structures:

Scaphotrapezial ligament
A thin palmar scaphotrapeziotrapezoid capsule/thick fibrous floor of the flexor carpi radialis tendon sheath
Scaphocapitate capsular ligament
Dorsal capsular ligament (minimal contribution to stability).

Scaphotrapeziotrapezoid articular injuries may be required for more advanced scapholunate instability patterns to exist.

FIGURE 10.89 ● (A) DISI with dorsal tilting of the lunate (curved arrow) without volar shift. Note the dorsal displacement of the capitate relative to the radius. The capitolunate angle (double-headed arrow) measures 32°. (B) Palmar tilting of the scaphoid (curved arrow) causes an abnormally increased scapholunate angle (double-headed arrow) of 124°. D, dorsal; V, volar.

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Tears of the scapholunate ligament are the most common type of carpal instability and may occur as a residual of a perilunate injury or as an isolated injury. They usually occur in adults, with an equal distribution between men and women, and are often associated with scaphoid and distal radial fractures. Sports that place dorsal stress on the carpus (loading the wrist in palmar flexion) put the scapholunate ligament at risk.

Etiology and Clinical Features

The mechanism of injury is axial compression/hyperextension with intercarpal supination or ulnar deviation, as would occur in a forward fall onto an outstretched hand or a backward fall on a pronated hand. Scapholunate dissociation requires injury to both the scapholunate intrinsic ligament and the extrinsic radioscaphocapitate ligament.

If an injury to ligamentous constraints occurs, such as a tear of the scapholunate ligament, the linkage between the scaphoid and lunate is removed and these bones become dissociated. A scapholunate ligament tear, however, may exist without a static instability (Fig. 10.88). In this case, the lunate is no longer under the influence of the scaphoid and instead follows the triquetrum, and the loading force of the capitate is not opposed by torque transmitted through the scapholunate ligament from the flexed scaphoid. Similarly, the lunate no longer exerts force on the scaphoid, and there is less opposing force to its flexion.

Radial deviation produces an exaggeration of the normal motions of the bones of the proximal row. With scapholunate interosseous ligament disruption, the scaphoid becomes more flexed in relation to the lunate, and the scapholunate angle, normally less than 30° to 60°, increases to more than 70° (Fig. 10.89). The scapholunate angle is determined from two sagittal images to demonstrate the separate lunate and scaphoid axes, which are not shown together in the same sagittal image. The lunate, free of the influence of the scaphoid, tips into a dorsiflexed position in relation to the axis of the capitate. As the scaphoid flexes, a gap appears between the scaphoid and the lunate, and in time the capitate will fall into this gap, contributing to a reduction in carpal height.

Rotatory subluxation of the scaphoid, which begins as an scapholunate dissociation, may also occur. In its final stages, as the lunate is dorsiflexed, a DISI pattern is established. On lateral radiographs, there is 10° or more of lunate dorsiflexion relative to the radius. On sagittal MR images, dorsal tilting of the lunate is associated with proximal migration of the capitate and loss of colinear alignment of the capitate, lunate, and radius. The capitolunate angle, normally 0° to 30°, can be directly measured on sagittal images and may be increased in dorsiflexion ligamentous instability.

Clinically patients present with pain and tenderness at the anatomic snuffbox. The Watson test (scaphoid shift test) for scapholunate ligament instability is positive, with pain on ulnar to radial deviation. and there is often an audible click at the scapholunate interval.

Pathologic Changes and MR Appearance

In evaluating scapholunate interosseous ligament pathology, MR imaging has an overall sensitivity rate of 93%, specificity of 83%, and accuracy of 90% when compared with arthrography.²³ In the diagnosis of ligament tears, with arthroscopy as the gold standard, MR imaging is 86% sensitive, 100% specific, and 95% accurate. The scapholunate ligament is uniformly visualized on coronal T2*-weighted images with 3-mm sections. In 90% of coronal plane images, the scapholunate ligament displays a triangular morphology; in 10% of cases, it demonstrates a linear morphology.⁵¹^,⁵⁹ In 63% of cases studied by Smith,⁵¹ the scapholunate ligament was seen as a homogeneous low- or low- to intermediate-signal-intensity structure. In 37% of cases, there were intermediate-signal-intensity areas traversing portions of the scapholunate ligament (part or all of the ligament), which could be potentially mistaken for a tear.

The following findings are characteristic of scapholunate ligament pathology:

Disruption of the scapholunate ligament is shown on T2*-weighted or STIR images as either complete ligamentous disruption or as a discrete area of linear hyperintensity in a partial or complete tear (Fig. 10.90).
In complete tears, synovial fluid communication between the radiocarpal and midcarpal compartments may be identified. Associated stretching (i.e., redundancy) or tearing of the radiolunate ligament and the radioscaphocapitate ligament is shown on sagittal images.
A flap tear may not be appreciated without the use of MR arthrography. MR arthrography is also helpful in evaluation of perforations and integrity of the dorsal component of the scapholunate ligament.
A perforation, identified by communication of fluid across a focal discontinuity, constitutes a communicating defect or tear. Small membranous perforations may exist in the presence of intact dorsal and volar portions of the scapholunate ligament. In fact, most degenerative perforations occur in the thin membranous portion of the scapholunate ligament, which is not thought to be biomechanically significant.⁵⁹^,⁶⁰
Partial-thickness perforations or noncommunicating defects may be associated with ligamentous tissue degeneration or sprains and may be difficult to appreciate on MR images.⁶¹
A complete scapholunate ligament tear may not be associated with scapholunate interval diastasis or static carpal instability as assessed on sagittal images, especially when the volar extrinsic ligaments are intact.
Axial MR images are used to distinguish among tears of the dorsal, membranous, and volar portions of the scapholunate ligament. The location of the tear can then be directly correlated with dorsal or volar coronal images.
The scaphoid attachment of the scapholunate ligament is more likely to avulse than is the stronger lunate attachment.⁵⁹ The insertion of the scapholunate ligament into hyaline cartilage covering the scaphoid is thus relatively weak. In fact, a scapholunate ligament

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tear may be associated with a scaphoid avulsion fracture (Fig. 10.91).
Potential sites of injury of the intrinsic scapholunate ligament complex (the scapholunate interosseous ligament) (Fig. 10.92) include its dorsal component (an important key stabilizer), a membranous component, and a volar component.
Less frequently injured is the extrinsic radiocarpal ligament complex, composed of the radioscaphocapitate, the long radiolunate (radiolunotriquetral), the short radiolunate, and the radioscapholunate (ligament of Testut). Associated synovitis, ganglions, or ligamentous hyperintensity may be seen in trauma.
The size of the tear varies depending on associated osseous or ligamentous disruption of major carpal links; the scaphotrapeziotrapezoid is the radial link and the triquetrohamate is the ulnar link.
Acute injuries (less than 6 weeks) may be classified as either stable injuries (partial ligament disruption) (Fig. 10.93) or dynamic or static unstable injuries (complete ligament disruption) (Fig. 10.94).
Chronic injuries are considered to be stable, unstable, or fixed. They are associated with a variety of secondary changes, including capsular contractures, degenerative arthritis, pancarpal arthrosis, intercarpal collapse, and SLAC wrist (progressive proximal capitate migration, radioscaphoid and capitolunate arthrosis in untreated scapholunate dissociation). DISI deformity with midcarpal collapse may also be seen.
The scaphoid attachment of the scapholunate ligament has fewer Sharpey's fibers than the lunate attachment and is therefore more susceptible to tearing (Fig. 10.95).

FIGURE 10.90 ● Scapholunate ligament tear with DISI. (A) Traumatic avulsion of the lunate aspect of the scapholunate ligament on a fast STIR coronal image. The scapholunate interval is widened with direct extension of fluid filling the tear site (large straight arrow). Ligament fibers are still attached to the radial aspect of the lunate (small straight arrow). Morphology is amorphous at the avulsed scaphoid remnant (curved arrow). (B) The capitolunate angle (arrow) is increased to 46°, and there is associated dorsal tilting of the lunate. (C) The scaphoid tilts palmarly with an increased scapholunate angle (arrow) of 142°.

In review, typical findings include:

Dissociation (Fig. 10.96), indicated by an increased scapholunate gap (more than 3 mm), comparable to the Terry Thomas sign on radiography
Volar or palmar flexion of the scaphoid on sagittal images (Fig. 10.97)
DISI with dorsal tilting of lunate, an increased capito-lunate angle (more than 30°), and an increased scapho-lunate angle (more than 80°) (Fig. 10.98)
Linear signal in a partial or complete tear
Complete ligamentous disruption with a fluid-filled gap and synovial fluid communication between the radiocarpal and midcarpal compartments
Disruption of the dorsal component of the scapholunate ligament
Associated synovitis of the extrinsic volar radiocarpal ligaments
Degenerative perforations in the membranous portion with intact volar and dorsal components (Fig. 10.99)
Associated dorsal ganglions in the dorsal or dorsal/membranous scapholunate ligament pathology (Fig. 10.100).

FIGURE 10.91 ● (A) T1-weighted and (B) STIR coronal images of a chronic avulsion fracture of the ulnar aspect of the scaphoid. The scapholunate ligament (straight arrow) is still attached to both the lunate and the surface of displaced scaphoid fracture fragment (curved arrow). S, scaphoid; L, lunate.

FIGURE 10.92 ● The scapholunate ligament forms a C-shaped complex, which is open distally at the level of the midcarpal joint. The membranous or proximal component forms the base of this C-shaped complex. The dorsal radiocarpal joint capsule inserts proximally into the dorsal component. The proximal aspect of the dorsal and volar components merges with the membranous component. Volarly, the radioscapholunate ligament inserts at the junction of the volar and membranous components of the scapholunate ligament.

FIGURE 10.93 ● Dorsal fiber disruption of the scapholunate ligament on color illustration (A) and coronal FS PD FSE image (B). Tearing of the strong dorsal fibers is frequently associated with either degeneration or tears of the membranous component. (C) Normal dorsal scapholunate ligament fibers shown for comparison.

FIGURE 10.94 ● Coronal FS PD FSE images showing complete disruption of the volar (A), membranous (B), and dorsal (C) components of the scapholunate (SL) ligament. (D) A corresponding axial T1-weighted arthrogram demonstrates lack of scapholunate ligament fibers from the dorsal to volar aspects of the interval.

FIGURE 10.95 ● Preferential disruption of the dorsal and membranous scapholunate ligament from the scaphoid, which has a weaker attachment to the interosseus ligament. Coronal FS PD FSE image.

FIGURE 10.96 ● Scapholunate (SL) dissociation (A) associated with disruption of all three components of the scapholunate ligament. (B). (A) Coronal FS PD FSE image. (B) Axial FS PD FSE image.

FIGURE 10.97 ● Scaphoid flexion (A) associated with disruption of the dorsal, membranous, and volar fibers of the scapholunate ligament (B). (A) Sagittal T1-weighted image. (B) Axial FS PD FSE image.

FIGURE 10.98 ● DISI deformity with lunate extension or dorsal tilting of the lunate and proximal movement of the capitate. DISI deformity is characterized by a scapholunate angle greater than 70°, a capitolunate angle greater than 20°, and a dorsiflexed and volarly displaced lunate. DISI deformity is not pathognomonic for scapholunate instability and can be associated with unstable scaphoid fractures (bony DISI), distal radius fractures (compensatory DISI), radius malunion (adaptive DISI), and capsular/ligamentous pathology, including scapholunate instability (ligamentous DISI). (A) Lateral graphic of DISI with dorsal tilting of the lunate. (B) Corresponding T1-weighted sagittal image of DISI with the concave surface of the lunate directed dorsally with proximal shift of the capitate.

FIGURE 10.99 ● Absence of membranous fibers of the scapho-lunate ligament allows direct extension of fluid from the radiocarpal joint. Coronal FS PD FSE image.

FIGURE 10.100 ● Dorsal ganglion communicating with a tear of the membranous scapholunate ligament with herniation of fluid through the dorsal scapholunate ligament fibers. (A) Coronal FS PD FSE image. (B) Axial FS PD FSE image.

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Classification

An arthroscopic classification scheme divides scapholunate ligament injury into four grades: grades I and II are partial tears and grades III and IV are complete disruptions. Perilunar instability (PLI) is divided into four stages:

Stage I: scapholunate failure
Stage I: capitolunate failure
Stage III: triquetrolunate failure
Stage IV: dorsal radiocarpal ligament failure with volar rotation of the lunate

Treatment

Conservative treatment with cast immobilization may be used, but surgery may be necessary. Surgical approaches for acute injury include close reduction and internal fixation or open reduction and primary repair or reconstruction. In chronic injuries, surgery includes open reduction and reconstruction or even arthrodesis.

The lunotriquetral ligament has dorsal, volar, and membranous (a fibrocartilaginous membrane) components. The lunate and triquetrum are stabilized by intrinsic and extrinsic carpal ligaments.

A loss of linkage (i.e., dissociation) between the triquetrum and the lunate, due to a tear of the lunotriquetral ligament, allows the lunate to follow the scaphoid. Under this influence, volarflexion of the lunate occurs and gives rise to a VISI pattern. VISI may be defined as a carpal instability characterized by proximal and volar migration of the bones of the distal row, associated with flexion of the lunate. The scapholunate angle is decreased to less than 30°, and the capitolunate angle may measure up to 30°.

Lunotriquetral ligament tears are less common than scapholunate ligament injuries and are considered part of the perilunar injury pattern. Membranous perforations are found in 13% of individuals over 40 years of age.

Etiology, Pathology, and Clinical Features

Pro-gressive perilunar injury/instability is caused by a palmar radial force with dorsiflexion and ulnar deviation. Lunotrique-tral ligament injury represents stage III PLI (triquetral dislocation with radiotriquetral ligament failure). It often occurs after scapholunate ligament injury or fracture (stage I PLI) and lunocapitate dissociation (stage II PLI). Perilunar instability results in DISI unless the scapholunate ligament heals, in which case the VISI pattern predominates (the forme fruste of stage III PLI). A perilunar pattern of injury is associated with intercarpal supination and injury from a radial to ulnar direction. An isolated lunotriquetral ligament sprain secondary to ulnar-sided injury is more common than concomitant radial injury. Reverse perilunar injury, which originates on the ulnar side of the wrist instead of the radial side, is caused by intracarpal pronation and radial deviation that force the capitate into the lunotriquetral joint. Isolated lunotriquetral ligament injury may also be seen with a palmarflexion mechanism of wrist injury. A combined scapholunate dissociation and lunotriquetral ligament injury is less common. Lunotriquetral ligament lesions may also be associated with inflammatory arthritis, increased load transmission across the ulnar side of the wrist, and ulnar positive variance (in particular, membranous lesions with ulnocarpal [ulnolunate] impaction are seen in positive ulnar variance).

Lunotriquetral Ligament Tear

Pathologic examination reveals a partial to complete lunotriquetral ligament tear and palmarflexion of the lunate. Fractures of the radial styloid or scaphoid may be seen as well as disruption of the scapholunate joint as part of stage III PLI. There is associated synovitis, joint wear/degeneration, abnormal ligament tension, and variable amounts of collagen fibers, connective tissue, and elastic fibers.

Symptoms vary depending on whether the tear is partial or complete. There may be a painful wrist click in radial or ulnar deviation, and stiffness, weakness, and instability are common. The history may include a traumatic event such as a fall on an outstretched hand or a twisting/rotatory injury. In complete lunotriquetral dissociation, there is static carpal collapse. Stress tests for lunotriquetral mobility, pain, and crepitus include the ulnar-side compression test, the lunotriquetral ballottement test, and the dorsal-palmar shear test.

Radiographic findings include disruption of the normal convex arc (Gilula's lines) of the proximal carpal row and a step-off between lunate and triquetrum.

MR Appearance

In the diagnosis of lunotriquetral interosseous ligament tears, MR imaging is 56% sensitive, 100% specific, and 90% accurate when compared with arthrography, and 50% sensitive, 100% specific, and 80% accurate when compared with arthroscopy.²³ Since the lunotriquetral ligament is less substantial than the scapholunate ligament, 3DFT coronal images may be needed to improve the sensitivity of diagnosis. Axial images are used to separate the volar, membranous, and dorsal components of the ligament since they are more difficult to appreciate on coronal images. In addition, unlike scapholunate dissociations, osseous widening of the lunotriquetral articulation is uncommon, which may make the detection of lunotriquetral ligament pathology more difficult, especially in the absence of adjacent fluid (secondary to an effusion or its introduction in MR arthrography). FS PD FSE sequences or MR arthrography is used for detection and characterization of insertional site tears, flap tears, perforations, separation of the individual lunotriquetral ligament components,

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associated TFC complex lesions, and associated chondral lesions of proximal lunate, triquetrum, and distal ulna in cases of positive ulnar variance. Improved visualization of radiocarpal and midcarpal communication is also afforded by these sequences.

Characteristic MR findings include the following:

Disruption of the lunotriquetral ligament is most frequently identified by a fluid-filled gap on coronal images (Fig. 10.101).
An insertional site tear or perforation is often appreciated on MR arthrography. FS PD FSE sequences provide sufficient contrast to produce an arthrogram-like effect without injection of contrast (Fig. 10.102).
Lunotriquetral ligament tears may be associated with TFC degenerative tears.⁴³
A VISI pattern usually requires disruption of both the lunotriquetral intrinsic and dorsal extrinsic ligaments (i.e., dorsal radiocarpal ligament).
Smith and Snearly⁵³ described the intact lunotriquetral ligament as linear in 63% and delta-shaped in 35% of asymptomatic individuals (Fig. 10.103).
The intact lunotriquetral ligament demonstrates homogeneous hypointensity in 73% and linear intermediate signal intensity within its substance in 25% of wrists studied.⁵³ Insertional signal intensity varies with the distribution of hyaline articular cartilage on either side of the lunotriquetral ligament.
Asymmetric hyaline articular cartilage signal intensity should not be mistaken for an eccentric tear unless fluid signal intensity communication is seen across the ligament cartilage interface. Linear fluid signal intensity communicating between the radiocarpal and midcarpal compartments through lunotriquetral space indicates tearing.
Sagittal MR images are used to assess static VISI instability with palmar tilting of the lunate and scaphoid (Fig. 10.104).
There may be discontinuity of the normal lunotriquetral ligament across the lunotriquetral interval (Fig. 10.105)
All lunotriquetral ligament components may be affected (Fig. 10.106), including the dorsal, membranous, and volar components.
The size of the tear varies based on associated injuries, including distal radioulnar joint subluxation and arthritis, chondromalacia of the distal ulna, TFC complex injury, and triquetrohamate instability.
There may be flap tears at the triquetral attachment or complete absence of the horseshoe-shaped ligament (Fig. 10.107).
Loss of the normal smooth convexity of the proximal carpal row is not uncommon.
Disruption of the lunotriquetral interval is pronounced with ulnar deviation.
There may be dorsiflexion of the triquetrum relative to the lunate on sagittal images.
On coronal images, triquetral offset may be distal relative to the lunate convexity.
An increased distance between the lunate and the triquetrum is sometimes seen, although it is not common (Fig. 10.108).
Extension of fluid is possible with membranous degeneration but intact dorsal and volar lunotriquetral ligament components.
The scapholunate angle is less than 30° to 40° and the capitolunate angle is greater than 10°.
Associated findings of ulnocarpal (ulnolunate) impaction are frequently seen with lunotriquetral ligament tears (Fig. 10.109).
Ganglions (Fig. 10.110) are less commonly associated with lunotriquetral ligament tears than with scapholunate ligament injury.

FIGURE 10.101 ● Tear with absence of the lunotriquetral ligaments (arrow) on FS T1-weighted arthrograms. The lunotriquetral ligament tear could be missed by using only gradient-echo sequence. L, lunate; T, triquetrum.

Treatment

Progression from minimal symptoms to ulnar wrist pain, a sensation of instability, ulnar nerve paresthesias, and eventual VISI deformity is typical. Conservative treatment includes immobilization, anti-inflammatory agents, and wrist splinting for acute injuries. Acute lunotriquetral dissociation with static deformity and chronic symptoms not responsive to immobilization may require surgery. Surgical treatment of lunotriquetral dissociations can be approached in two ways. If there is no VISI and positive ulnar variance is present, ulnar shortening unloads the lunotriquetral interval and provides excellent symptomatic relief. The torn lunotriquetral ligament should be repaired if possible. Lunotriquetral intercarpal fusion is also an option, although meticulous technique is required to avoid pseudoarthrosis. Lunotriquetral fusion is an attractive concept because this is the most common carpal coalition. These coalitions are usually asymptomatic and are

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often diagnosed in radiographs taken for other reasons. However, achieving a stable lunotriquetral fusion has proven difficult, and most series show significant rates of nonunion (i.e., up to 40%). Techniques using larger bone grafts and compression fixation devices have improved the success of this procedure. We have had 100% success in achieving fusion using the Herbert bone screw with precompression of the fusion site.

FIGURE 10.102 ● Flap tear of the lunotriquetral ligament associated with TFC tear and proximal lunate chondromalacia. Coronal FS PD FSE image.

FIGURE 10.103 ● Normal variants of the lunotriquetral interosseous ligament. (A) Eccentric ulnar position of the delta-shaped lunotriquetral ligament with intermediate-signal-intensity hyaline cartilage seen on the lunate insertion (white arrows) of the ligament. There is direct contact between the lunotriquetral ligament and the low-signal-intensity cortex of the triquetrum (black arrows). (B) Commonly seen linear morphology of the lunotriquetral ligament (arrow). There is no hyaline cartilage signal intensity at the insertion sites of the ligament. T, triquetrum; L, lunate.

FIGURE 10.104 ● A VISI pattern is apparent in clinical midcarpal instability. This sagittal T1-weighted image shows the volar tilt of the lunate (curved black arrow), increased capitolunate angle, and subchondral sclerosis of the opposing surfaces of the capitate (straight black arrow) and lunate (white arrow). The ulnar arm of the arcuate ligament is not visible in midcarpal instability. MR imaging was the first modality able to document degeneration of the proximal pole of the capitate in subluxation of the capitate on the lunate.

Classification of Wrist Instabilities

There are numerous classification schemes for instability of the carpus. The most useful classification reflects the anatomy and pathophysiology of the condition and indicates treatment. Four characteristics are described in classification of carpal instabilities:

Severity (categorized as dynamic, static subluxation, or static dislocation)
Direction of displacement: dorsal (DISI), volar (VISI), or radioulnar/proximodistal translation (e.g., ulnar, radial, distal, proximal)
Location of injury
Type of injury

Proximal or distal displacements are represented by axial carpal dislocations.⁶² These are rare traumatic injuries, usually associated with a crush or blast mechanism. There is a longitudinal transarticular derangement of both the carpal and metacarpal transverse arches, with complete loss of the normal relationship between the two columns of the carpus. The radiologic hallmarks are an abnormal widening of any joint between the bones of the distal carpal row, a disruption of Gilula arc III defined by the proximal articular surfaces of the bones of the distal row, and an abnormal gap between the bases of two adjacent metacarpals.⁶³ Gilula's arcs are used to demonstrate parallelism of the articular alignment of the carpal bones. A disrupted arc with widening or offset of joint spaces is associated with ligamentous, osseous. or joint injury.

Carpal instabilities can be grouped into perilunar (perilunate) instabilities, midcarpal instabilities, and proximal carpal instabilities.

Perilunate instabilities may be divided into lesser and greater arc injuries. Lesser arc injuries involve disruptions that follow the contour of the lunate itself, whereas greater arc injuries are transscaphoid, capitate, hamate, or triquetral. Perilunar instability includes dorsal perilunate dislocation and palmar lunate dislocation.

Lesser arc injuries involve scapholunate ligament, lunotriquetral ligament, and complete perilunate instabilities.
Greater arc injuries are divided into scaphoid fractures, naviculocapitate syndrome (scaphoid fracture plus perilunate dislocation), and transscaphoid transtriquetral perilunate dislocation.

Mayfield's spectrum of progressive lunate instability is shown in four stages.⁶⁴ The stages were defined experimentally in cadaver wrists by in vitro simulation of a fall on an outstretched hand. The wrist was forced into progressive dorsiflexion, ulnar deviation, and intercarpal supination, and progressive injuries were noted:

Stage I: The scapholunate ligament fails, leading to an scapholunate ligament instability.
Stage II: There is progression to failure of the midportion of the radioscaphocapitate ligament.
Stage III: There is failure of the capitolunate and triquetrolunate joints with failure of the radiotriquetral ligaments.
Stage IV: There is failure of the dorsal radioscapho-lunotriquetral ligament, resulting in complete palmar dislocation of the lunate.

Midcarpal instabilities are classified as intrinsic (ligamentous laxity) or extrinsic in origin. Intrinsic instabilities include palmar midcarpal instability (a VISI pattern) and dorsal midcarpal instability (a DISI pattern). In patients with palmar midcarpal instability, ulnar deviation with load on the wrist (i.e., a clenched fist placing a transcarpal load) produces a painful clunk. This clunk represents relocation of the midcarpal joint

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as the wrist moves into ulnar deviation. This instability is due to a congenital or acquired laxity of the ulnar arm of the volar arcuate ligament. This is a true transverse laxity, as all of the instability occurs between the proximal and distal rows. This subluxation/relocation can be prevented by a dorsally directed force on the pisiform, which reduces the static VISI of the proximal row. On cine films, the proximal carpal row suddenly snaps from a volar-flexed position to a dorsal or neutral position. This movement is in contrast to the smooth, fluid transition seen in the normal wrist. Dorsal midcarpal instabilities are most commonly seen after malunion of a distal radius fracture that leaves the distal radius articular surface in a dorsiflexed position. Correction with an osteotomy of the distal radius restores the normal volar tilt.

FIGURE 10.105 ● Comparison of normal intact lunotriquetral ligament (A) with an ulnar-sided lunotriquetral ligament tear at the triquetral attachment (B). (C) Normal congruity of carpal arcs. Arc 1 connects the proximal articular surfaces of the scaphoid, lunate, and triquetrum. Arc 2 connects the distal concave surfaces of the scaphoid, lunate, and triquetrum. Arc 3 outlines the proximal convexity of the capitate and hamate. (A) Coronal FS PD FSE image. (B) Coronal T1-weighted arthrogram. (C) Coronal color illustration.

FIGURE 10.106 ● Coronal FS PD FSE images showing tear of the dorsal (A), membranous (B), and volar (C) components of the lunotriquetral (LT) ligament. Offset of the normally congruous lunatotriquetral arc (B) is a secondary sign of lunotriquetral ligament tear and instability.

FIGURE 10.107 ● Volar component tear of the lunotriquetral (LT) ligament. (A) Coronal color illustration. (B) Coronal FS PD FSE image.

FIGURE 10.108 ● Lunotriquetral (LT) ligament diastasis associated with lunotriquetral ligament and TFC disruption. Coronal FS PD FSE image.

Proximal carpal instabilities are classified as:

Ulnar translocation of the carpus (secondary to rheumatoid disease or trauma, or iatrogenically introduced by excision of the ulnar head or radial styloid)
Dorsal instability (secondary to a dorsal rim distal radial fracture'a dorsal Barton's fracture)
Palmar instability (secondary to a volar rim distal radial fracture'a volar Barton's fracture)

DISI and VISI instabilities can each be further subdivided into nondissociative carpal instabilities and dissociative carpal instabilities. In this context, nondissociative means that the intercarpal ligaments are intact and that the bones of the row are moving together. Dissociative means that one or more of the intercarpal ligaments is incompetent and the bones of the row

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no longer move together.⁶⁵ There are three major types of injuries:

Carpal instabilities, dissociative are injuries affecting intracapsular intercarpal ligaments, as described in the earlier examples.
Carpal instabilities, nondissociative are injuries involving the capsular ligaments with no dissociation of the carpal bones themselves.
Complex carpal instabilities are injuries that involve both dissociative and nondissociative elements.

FIGURE 10.109 ● Ulnocarpal (ulnolunate) impaction with positive ulnar variance, TFC degenerative tear, and lunotriquetral (LT) ligament disruption. Lunate and triquetral proximal cystic change and sclerosis and edema may be visualized on either side of the lunotriquetral interval. Coronal FS PD FSE image.

FIGURE 10.110 ● Dorsal lunotriquetral (LT) ligament ganglion overlying dorsal fibers on a coronal FS PD FSE image.

The more common pattern of dissociative instabilities includes complete tears of either or both of the intrinsic ligaments of the proximal carpal row (scapholunate and lunotriquetral) and transscaphoid fractures. A transscaphoid fracture is the equivalent of a tear of the scapholunate ligament, leading to a dissociative instability as the scaphoid and lunate become unlinked through the fracture site.⁶⁶ There is usually associated disruption or attenuation of the palmar or dorsal extrinsic ligaments.

In nondissociative instabilities, there may be carpal malalignment with intact interosseous ligaments. There may also be attenuation of the palmar or dorsal radiocarpal liga-ments. The proximal carpal row is usually palmar (nondisso-ciative VISI). Nondissociative instability may be secondary to distal radius fracture (in which there is loss of normal volar angulation of the distal radius), ulnar plus variance, midcarpal instability, and abnormalities of the scaphotrapeziotrapezoid joint.⁶⁷

Carpal instability, dissociative may be diagnosed if there is radiographic or arthroscopic evidence of dissociation between rows as well as within rows. Disruption affects both the intercarpal and the capsular wrist ligaments. In the dissociated form of DISI, there is extension of the scaphoid and lunate, whereas extension does not occur in the interosseous ligaments. The same holds true for VISI. In carpal instability, dissociative, there is flexion of the scaphoid and triquetrum; in nondissociative instability, there is no flexion of these bones.

In scapholunate dissociation, there is dissociative DISI. There is often a history of a dorsiflexion injury, secondary to a fall, and the development of scapholunate interval tenderness. The physical examination is distinctive in these patients. They cannot bear weight on the wrist in dorsiflexion, and the Watson-Shuck test, a drawer test for the scapholunate ligament, is positive. Sagittal MR scans, like lateral radiographs, demonstrate an increased scapholunate angle (greater than 60°) with dorsal angulation of the lunate and triquetrum, and an increased capitolunate angle (greater than 15° compared with the normal capitolunate angle of 30°). There is palmar flexion of the scaphoid. On coronal MR images, a scapholunate gap of more than 4 mm may be seen.

With nondissociative DISI, a secondary disorder may develop, characterized by proximal row extension in response to dorsal angulation of a malunited distal radius fracture. There may be damage to the ligaments that stabilize the midcarpal joint.

Lunotriquetral ligament instability represents dissociative VISI. There is a flexed lunate and the scapholunate angle is decreased to less than 30° with lunate and scaphoid volar flexion. Acute lunotriquetral dissociation is often associated with a history of a rotational injury to the wrist with the development of ulnar-sided pain.

Midcarpal Instabilities

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In nondissociative VISI, there is a decreased or normal scapholunate angle, lunate flexion, and a decreased capitolunate angle of less than 15°. There is flexion of the proximal carpal row with a normal scapholunate interval. Nondissocia-tive VISI is usually a chronic condition associated with generalized ligamentous laxity.

The arcuate ligament complex is the major stabilizer of the midcarpal joint. The ulnar arm of the arcuate ligament consists of the triquetrohamatocapitate ligament and the radial arm extends from the distal aspect of the radioscaphocapitate ligament. The space of Poirier is a weak area between the capitate and lunate. Midcarpal instability may be palmar, less commonly dorsal, or extrinsic. Midcarpal instability is seen less often than scapholunate dissociation and approximately the same or more often than lunotriquetral ligament instability. It is characterized by a lack of support of the proximal carpal row and the midcarpal joint and loss of the normal joint forces between proximal and distal carpal rows. VISI may be seen on sagittal MR images.

Etiology, Pathology, and Clinical Features

Injury to the ulnar arm of the arcuate ligament is the most common mechanism in midcarpal instability. Dorsiflexion, flexion, compression, rotation, and distraction injuries may all cause midcarpal instability. Approximately 50% of patients report a history of minimal trauma.

As mentioned, midcarpal instability may be palmar, dorsal, or extrinsic (secondary to distal radius malunion). Palmar midcarpal subluxation, classified as ulnar midcarpal instability or carpal instability, nondissociative, is the most common pattern of midcarpal instability and was first studied by Lichtman et al.⁶⁸ Patients present with palmar subluxation at the midcarpal joint and a painful clunk with ulnar deviation of the wrist. This instability is due mainly to laxity of the ulnar arm of the volar arcuate ligament.⁶⁸ There is also evidence of increased laxity of the dorsal radiolunotriquetral ligament, which functions as a checkrein to prevent flexion of the proximal carpal row, and sagittal MR images show palmarflexion of the lunate, as in a VISI pattern.

In ulnar deviation, the excessive volar tilt of the lunate allows the head of the capitate to sublux volarly into the space of Poirier. With radial deviation, the lunate dorsiflexes, and there is relocation of the capitate. This type of instability is classified as dynamic carpal instability, nondissociative, since there is no dissociation of the carpal bones. The intensity of the clunk and the pain increase with loading of the capitolunate joint, as occurs when the fist is clenched. Dorsally directed pressure on the pisiform eliminates this subluxation, and Lichtman et al. have designed dynamic splints that apply this directional force and relieve symptoms. This dorsally directed pressure on the pisiform can also be used to diagnose palmar midcarpal subluxation.

Dorsal midcarpal instability is associated with laxity of the palmar radioscaphocapitate ligament. Dynamic midcarpal instability centered on the lunocapitate joints has been described as a capitolunate instability pattern (CLIP). There is no underlying DISI or VISI pattern of instability.

There are also extrinsic causes for midcarpal instability or carpal instability, nondissociative. Extrinsic midcarpal instability is associated with dorsal displacement and angulation of the distal radius and an adaptive Z-deformity of the carpus. Taleisnik and Watson⁷⁰ have described the extrinsic causes in conjunction with malunited fractures of the distal radius. In these cases, there is dorsal angulation of the distal radial articular surface that results in dorsiflexion of the lunate and dorsal subluxation of the midcarpal row. This instability can be treated with an osteotomy of the distal radius to restore its normal volar tilt.

Another type of carpal instability, nondissociative, involving the radiocarpal and ulnocarpal joints, occurs more proximally. Ulnar translation of this type is commonly seen in rheumatoid arthritis. Normally, the volar radiocarpal ligaments, which originate from the region of the radial styloid, act as guide to keep the carpal bones (i.e., scaphoid and lunate) well seated in their fossae in the distal radius. In rheumatoid arthritis, however, destructive synovitis weakens the radioscaphocapitate and radiolunate ligaments, and the carpus begins to migrate down the inclined plane of the distal radius in an ulnar direction. The distance between the radial styloid and scaphoid increases, as can be seen on PA radiographs or coronal plane MR images. Resection of the distal ulna (i.e., Darrach procedure) also results in loss of the buttressing effect of the ulna and increased ulnar translation.⁷¹ Posttraumatic ulnar translocation of the carpus has also been described.⁷²

Proximally occurring cases of carpal instability, nondissociative, may also be seen with dorsal or volar displacements. Patients with malunited dorsal or volar intra-articular fractures lose the stability that the bony contour of the distal radius provides. This allows the proximal row to slip dorsally or volarly, depending on whether the malunited fracture is dorsal or volar.

Clinically, patients present with a clunk on ulnar deviation with the forearm in pronation (“catch-up clunk”) and may or may not have a history of trauma. There is an asymptomatic phase prior to presentation, which is sometimes bilateral. Other signs and symptoms include:

A palmar sag of the ulnar side of the carpus
A prominent ulnar head with the wrist in neutral deviation
Localized synovitis
Tenderness over the ulnar carpus and triquetrohamate joint
Active ulnar deviation of pronated wrist reproduces the clunk.
With extreme ulnar deviation (after the clunk), the volar sag of the ulnar carpus is absent.
A positive midcarpal shift test (a painful clunk with passive ulnar deviation)

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MR Appearance

The best indication of midcarpal instability is VISI on sagittal images. The VISI pattern is characterized by a volar tilt of the lunate and palmarflexion instability and translocation of the distal row as described earlier. Additional MR findings in midcarpal instability include:

Sclerosis between the distal lunate and the proximal capitate
An attenuated or disrupted lunotriquetral ligament
Fluid extension across the lunotriquetral or scapholunate interval
Synovitis, attenuation, or laxity of the ulnar arm of the arcuate ligament (Fig. 10.111) and dorsal radiotriquetral ligament (in palmar midcarpal instability) (Fig. 10.112)
Ulnar minus variance
Associated extension of contrast directly communicating across the scapholunate or lunotriquetral interval on MR arthrograms

FIGURE 10.111 ● Palmar midcarpal instability (MCI) is the most common pattern of midcarpal instability. Palmar MCI is associated with laxity of the ulnar arm of the arcuate ligament and the dorsal radiotriquetral ligament with palmar (volar) translation of the distal carpal row. (A) Laxity of the ulnar arm of the arcuate ligament on a coronal FS PD FSE image. (B) Coronal illustration of the lax ulnar arm of the arcuate ligament. (C) Coronal illustration of the lax radioscaphocapitate ligament as seen in dorsal midcarpal instability in contrast to palmar midcarpal instability. Dorsal midcarpal instability is a much less common variant of midcarpal instability.

Treatment

In time, dynamic instability becomes fixed VISI and there is loss of the physiologic VISI to DISI with radial to ulnar deviation. The proximal carpal row remains flexed and the distal row palmarly subluxed until extreme ulnar deviation. With ulnar deviation of the wrist the distal row abruptly reduces and the proximal row snaps into extension (“catch-up clunk”). Conservative treatment includes activity modification for milder cases, nonsteroidal anti-inflammatory medications, steroid injections, wrist immobilization, and dorsally directed pressure on the pisiform with a splint (which reduces ulnar carpal sag and VISI). The midcarpal position may be restored by activating the hypothenar muscles and the extensor carpi ulnaris and flexor carpi ulnaris. Surgical approaches include ligament reconstruction, capsular tightening, and limited midcarpal arthrodesis. A more

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detailed discussion of the treatment of carpal instability is found below.

FIGURE 10.112 ● (A) The course of the dorsal radiotriquetral ligament, which passes obliquely across the dorsal surface of the lunate (to which it is attached) and terminates in the dorsal triquetrum. A fracture fragment of the lip of the distal radius is attached to the proximal radiotriquetral ligament on this PD-weighted coronal image. (B) Coronal illustration with lax radiotriquetral ligament (dorsal view).

Other Static Ligamentous Instabilities

In ulnar translocation, the carpal bones are ulnar in position, the scapholunate and capitolunate (CL) angles are normal, and the space between the scaphoid and the radial styloid increases. Greater than 50% of the lunate is medial to the radius (as assessed on a neutral PA radiograph). Ulnar translocation may be caused by synovial-based disorders, as well as by severe trauma or surgical excision of the ulnar head or radial styloid.

In dorsal subluxation, the carpal bones occupy a dorsal position relative to the midplane of the radius. The scapholunate and CL angles are normal. There is often an associated dorsally impacted distal radius fracture.

In palmar subluxation, the carpal bones are palmar to the midplane of the radius. The scapholunate and CL angles are normal, and there may be associated ulnar translocation.

Treatment of Carpal Instabilities

Treatment for most of the carpal instabilities remains controversial. This is especially true of dissociative instability. In general, the goal of most surgical approaches is to restore the anatomy and biomechanics of the injured part of the carpus.

Carpal Instability, Nondissociative

In the extrinsic forms of nondissociative carpal instability caused by malunited fractures of the distal radius, surgical correction of the instability is aimed at restoring the anatomy of the radius. In rheumatoid arthritis, however, the injured soft-tissue constraints seen in nondissociative carpal instability with ulnar translation cannot be reconstructed surgically. Reduction of the carpus and radiolunate fusion may be successful in preventing recurrence of ulnar translation. The lunate, when fused to the radius, acts as a doorstop and prevents the carpus from sliding down the inclined plane of the radius.

Nondissociative carpal instability associated with dorsal midcarpal instability secondary to a malunited distal radius fracture with dorsal tilt of the articular surface can be treated with an osteotomy of the distal radius, which restores normal volar angulation.

Nondissociative carpal instability with palmar and carpal instability presents a more difficult problem. The pathology is excessive volar tilt of the lunate caused by laxity of the ulnar arm of the volar arcuate ligament. Lichtman and others have devised a soft-tissue reconstruction that consists of tightening the volar arcuate and dorsal radiolunate ligaments to correct the excessive VISI of the lunate. This procedure has been successfully performed in a small number of patients. A more reliable operation is the four corner fusion' an intercarpal fusion of the lunate-triquetrum-capitate-hamate. Although some range of motion is lost with this procedure, it has been quite successful in eliminating the clunk since the subluxing joint is fused.

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Carpal Instability, Dissociative

There is debate on the treatment of the various forms of dissociative carpal instability. In many cases, these conditions remain unsolved problems; scapholunate dissociation is an excellent example. Early cases of ligament rupture without rotatory subluxation can usually be satisfactorily treated by pinning the scapholunate ligament and performing open suture repair of the torn ligament, followed by immobilization.⁷³ Accurate reduction is necessary to align the ligament fibers for optimal healing. Once rotation of the scaphoid is accomplished, the proximal pole must be reduced in relation to the lunate and a procedure performed to hold it firmly in place. Ligament reconstructions similar in concept to those devised for the anterior cruciate in the knee have met with uniformly poor results.⁷⁴ When the scaphoid rotates or flexes, its proximal pole becomes incongruent in the radial fossa. Several methods use intercarpal fusions to ensure that the proximal pole remains congruent in the scaphoid fossa of the radius. Watson and Mempton have reported on the successful use of triscaphe (i.e., scaphoid-trapezoid-trapezius) arthrodesis.⁷⁵ Others have performed scaphocapitate fusions with similar results. An alternative to intercarpal fusion is dorsal capsulodesis.⁷⁶ In this procedure, a strip of the dorsal capsule of the wrist is left attached proximally to the radius on one end, and the other is inserted into the distal pole of the scaphoid. By pulling dorsally on the distal pole, the scaphoid is held in a horizontal, reduced position. If possible, the scapholunate ligament should be repaired.

Distal Radioulnar Joint

The ulna articulates with the distal radius through the sigmoid or ulnar notch.⁷⁷ The distal or inferior radioulnar compartment extends proximally as far as the synovium-lined recessus sacciformis. The distal ulna is wrapped in the extensor retinaculum but is not directly attached to it. The extensor carpi ulnaris tendon is deep to the extensor retinaculum and has a subsheath attachment to the distal ulna. The articular disc, or TFC, is composed of collagen and elastic fibers, is triangular, and bridges the distal ends of the radius and ulna. The volar aspect of the TFC has strong attachments to the lunotriquetral and ulnotriquetral ligaments and a weaker attachment to the ulnolunate ligament. There is 150 of forearm rotation at the distal radioulnar joint, with rotation of the distal radius around the ulnar head. In pronation and supination, the ulnar head moves dorsally and palmarly, respectively, in the sigmoid notch (Fig. 10.113). Contact between the ulnar head and the sigmoid notch is greatest during forearm midrotation and least in maximum pronation or supination. These are the positions most commonly used in imaging the wrist with a dedicated wrist coil. Relative to the distal radius, the ulnar head moves distally in pronation and proximally in supination. The distribution of load across the wrist is 82% through the distal radius and 18% through the distal ulna. After complete excision of the distal ulna, the TFC complex supports a portion of the ulnar forces that are unloaded.⁷⁷ In ulnar deviation, there is increased ulnar load transmission.

FIGURE 10.113 ● Normal biomechanics of the distal radioulnar joint. (A) Mild dorsal shift of the ulna relative to the sigmoid notch of the distal radius in full pronation is normal. The extensor carpi ulnaris tendon is located within its groove in the medial distal aspect of the ulna. (B) Mild volar shift of the ulna in full wrist supination is normal. The extensor carpi ulnaris tendon may be located within its ulnar groove or subluxed medially in extreme supination, as shown in this example.

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Ulnar Variance

The concept of ulnar variance is critical in the management of distal radial fractures, in the pathogenesis of Kienböck's disease, and in TFC pathology. Ulnar variance refers to the relative lengths of the radius and ulna and can be defined as the relative level of the distal end of the ulna to that of the radius. If the ulna is short, ulnar variance is considered negative (Fig. 10.114). If the ulna is long, the variance is referred to as positive (Fig. 10.115). Neutral ulnar variance occurs when the lengths of the radius and ulna are relatively equal. Radiographically, the relative lengths of the radius and ulna are measured from the centers of their distal articular surfaces. There are three commonly used methods for measuring ulnar variance, and all three are similarly accurate and reliable.⁷⁸ Wrist position is an important determinant of ulnar variance. Supination causes relative ulnar shortening, and pronation causes lengthening.⁷⁹ For this reason, it is critical that ulnar variance be determined with the forearm and wrist in 0 of pronation and supination.

Ulnocarpal (Ulnolunate) Abutment (Impaction) Syndrome

Ulnocarpal abutment, also known as ulnar impaction syndrome, ulnolunate abutment, ulnolunate impaction syndrome, ulnar impaction, and ulnocarpal loading, is a degenerative condition caused by excessive load-bearing across the ulnar aspect of the wrist. It occurs most often in middle-aged individuals (50 years of age or more), and there is no gender bias.

An understanding of the relevant anatomic structures helps elucidate the lesion. The TFC represents the articular disc (centrum) and the dorsal and volar radioulnar ligaments. The TFC complex consists of the TFC, the meniscus homologue (the ulnocarpal meniscus), the ulnar collateral ligament, the sheath of the extensor carpi ulnaris, and the ulnolunate and ulnotriquetral ligaments. Pronation causes relative ulnar lengthening, and the lunate articulates with the lunate facet of the distal radius and the TFC. Although ulnocarpal (ulnolunate) abutment most commonly occurs when there is excessive positive ulnar variance,⁷⁷^,⁸⁰ the presence of positive ulnar variance is not required for the diagnosis. The term ulnar impingement syndrome should be reserved for cases of impingement of the ulna against the shaft of the radius, as may occur after excessive Darrach-type shortening of the ulna.⁸⁰

Etiology, Pathology, and Clinical Features

In ulnocarpal abutment syndrome, there is painful compression of the distal ulna on the medial surface of the lunate. It is not un-usual to see full-thickness defects of the cartilage of the lunate as well as degeneration and tears of the TFC. TFC perforations are relatively common and are seen in 40% of the population by the end of the fifth decade. In 73% of wrists with degenerative TFC perforation and ulnar and lunate erosions, there is positive or neutral ulnar variance as seen in the ulnocarpal abutment syndrome. In extreme cases of excessive ulnar length, common in patients with rheumatoid arthritis, there may be dorsal subluxation of the ulna, and supination is blocked. Severe dorsal subluxation with supination of the carpus is common. Attritional ruptures of the extensor tendons of the fourth and fifth compartments often occur due to erosion caused by the prominent ulna. Lunotriquetral ligament disruption may also be seen, as well as central attenuation of the TFC in positive ulnar variance and degeneration of the avascular central articular disc of the TFC. Lunate sclerosis is usually restricted to the proximal ulnar lunate, involving less than 40% of the subchondral area. There may be chondromalacia of the distal ulna, the proximal lunate,⁸¹ and the triquetrum.

Ulnocarpal abutment may be acquired or congenital. Acquired lesions are usually associated with trauma, often distal radius fractures⁸² with shortening and angulation and fractures with ligamentous injuries of the distal radioulnar joint (e.g., Galeazzi and Essex-Lopresti fractures). Congenital disease may be associated with Madelung's deformity (dyschondroplasia) and ulnar plus variance (the increased ulnar length results in increased forces across the ulnocarpal articulation).

Clinically patients present with chronic or subacute dorsal pain and discomfort. The pain increases with extremes of rotation and ulnar deviation and may be accompanied by intermittent clicking and swelling. Patients report decreased strength and range of motion. In cases of lunotriquetral ligament disruption, there is discomfort with loading of the lunotriquetral joint. In contrast to distal radioulnar joint pathology, pain is not present throughout the entire range of pronation to supination. There may or may not be a history of trauma, positive ulnar variance, and tenderness between the ulnar head and the triquetrum and lunate.

Classification

Ulnocarpal (ulnolunate) abutment is equivalent to Palmer class II degenerative lesions of the TFC complex. Class II lesions are further subdivided into five types:⁸³

Palmer class IIA lesions represent TFC complex wear.
Palmer class IIB lesions represent TFC complex wear and lunate, triquetrum, and possibly ulnar chondromalacia.
Palmer class IIC lesions represent TFC complex perforation and lunate, triquetrum, and possibly ulnar chondromalacia.
Palmer class IID lesions represent TFC complex perforation and lunate, triquetrum, and ulnar chondromalacia and lunotriquetral ligament perforation.
Palmer class IIE lesions represent TFC complex perforation and lunate, triquetrum, and ulnar chondromalacia, lunotriquetral perforation, and ulnocarpal arthritis.

FIGURE 10.114 ● Negative ulnar variance with the articular surface of the ulna projecting proximal to the articular surface of the radius. In cases of severe negative ulnar variance, the TFC has a deformed morphology and extends proximally.

FIGURE 10.115 ● Positive ulnar variance with the articular surface of the ulna projecting distal to the lunate fossa of the distal radius. There are initial changes of ulnocarpal (ulnolunate) abutment with subchondral edema of the proximal lunate. Coronal FS PD FSE image.

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MR Appearance

With the exception of positive ulnar variance or a prominent ulnar styloid, plain radiographs in patients with early ulnocarpal (ulnolunate) impaction (abutment) are unremarkable. Later, subchondral sclerosis and cystic degeneration can be seen along the proximal, adjacent borders of the triquetrum and lunate. Bone scintigraphy may show nonspecific uptake in the ulnolunate region. MR imaging may demonstrate central perforations of the TFC in association with neutral or positive ulnar variance (Fig. 10.116). These tears occur between contact surfaces of the lunate and ulna. MR imaging also allows detection of the earliest development of subchondral sclerosis and cystic changes on the ulnar aspect of the lunate. Sclerotic changes demonstrate low signal intensity on T1-, PD-, and FS PD FSE images. The cystic degeneration demonstrates low or low to intermediate signal intensity on FS PD FSE images. Coronal scans reveal the initial degenerative changes in the articular cartilage of the distal ulna, proximal lunate, or proximal triquetral surfaces. These degenerative changes are indicated by either attenuation of articular cartilage or irregularity or denuding of the articular cartilage surface. Another feature of the ulnolunate abutment syndrome that can be documented on coronal and sagittal MR images is lunotriquetral ligament disruption and resultant instability.

Key MR findings include:

Eccentric sclerosis of the proximal ulnar aspect of the lunate and the proximal radial aspect of the triquetrum
Subchondral sclerosis and cystic changes occur more often in the lunate than in the triquetrum.

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Normal marrow fat signal distal and radial to the sclerosis in the lunate
Neutral or positive ulnar variance, although less commonly there may be negative ulnar variance
Possible associated trauma to the distal radius or ulnar styloid
Attenuated centrum or a central perforation of the TFC
Chondromalacia involving the articular cartilage of the ulna (Fig. 10.117)
Fluid across the torn lunotriquetral ligament or lunate-triquetrum proximal arc offset associated with lunotriquetral ligament tear

FIGURE 10.116 ● (A) Coronal color illustration of ulnocarpal (ulnolunate) abutment with associated lunotriquetral ligament tear. TFC perforation and reactive subchondral edema are shown in the lunate and triquetrum. Coronal T1-weighted (B) and FS PD FSE (C) images demonstrate ulnar-sided eccentric sclerosis and edema of the proximal lunate in conjunction with positive ulnar variance.

The differential diagnosis of ulnocarpal (ulnolunate) abutment includes both Kienböck's disease and ulnar impingement. In Kienböck's disease there is AVN of the lunate related to trauma and negative ulnar variance. The pattern of lunate sclerosis is more centralized, and a discrete lunate fracture may be visualized. Ulnar impingement syndrome differs from ulnocarpal impingement: in ulnar impingement there is negative ulnar variance with a scalloped concavity of the ulnar aspect of the distal radius (Fig. 10.118). There is convergence of the ulna toward the distal radius with pain on pronation and supination. Degenerative sclerosis and hypertrophic osteophytes (Fig. 10.119) are associated findings at the distal radioulnar joint.

Treatment

With continued increased load transmission through the ulna, there is progression of symptoms. Treatment must address malunion of distal radial fractures, physeal arrest, Essex-Lopresti injury (fracture/dislocation of the radial head and dislocation of the distal radioulnar joint), and positive ulnar variance. Conservative measures include activity modification and anti-inflammatory medication. Surgery is geared toward unloading the distal ulna to relieve pain and halt the progression of impingement. An ulnar shortening osteotomy is the procedure of choice. Other options include TFC complex débridement, the wafer procedure (resection of the distal ulna beneath the TFC), and hemiresection of the distal ulna. Arthroscopic approaches are used except for ulnar shortening osteotomy. The Sauvé-Kapandji procedure involves fusion of the distal radioulnar joint. Complications include weakness and instability after the Darrach procedure (resection of the distal ulna), impingement after hemiresection, and instability after a Sauvé-Kapandji procedure.

Instability of the Distal Radioulnar Joint

Distal radioulnar joint instability is a loss of the normal anatomic or kinematic relationship between the distal radius and ulna with the carpus. It may be secondary to a sprain, dislocation or malalignment of a forearm bone fracture, synovitis, or ligamentous laxity.⁸⁴^,⁸⁵ It most often occurs in those at risk

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for Colles', Smith's, Galeazzi's, and Essex-Lopresti fractures. A younger population is at risk for traumatic injury and older individuals are at risk for injury associated with osteoporosis.

Pearls and Pitfalls

Instability of Distal Radioulnar Joint

Axial images in full pronation and supination are used to identify the location of the ulna relative to the sigmoid notch.
The dorsal and volar radioulnar ligaments of the TFC are evaluated on coronal, axial, and sagittal images.
Ulnar dorsal dislocation in hyperpronation is associated with disruption of the volar distal radioulnar ligament.
Ulnopalmar (ulnovolar) dislocation in hypersupination occurs with disruption of the dorsal distal radioulnar ligament.

FIGURE 10.117 ● Chondromalacia involving subchondral cystic change of the proximal ulnar aspect of the lunate and proximal radial aspect of the triquetrum in ulnocarpal (ulnolunate) abutment. There is disruption of the lunotriquetral ligament of the TFC. (A) Coronal PD FSE image. (B) Coronal T2* gradient-echo image.

FIGURE 10.118 ● Radioulnar impingement with degenerative distal radioulnar joint changes, including subchondral cysts, chondromalacia, and TFC degeneration. Coronal T2* gradient-echo image.

FIGURE 10.119 ● Hypertrophic osteophyte associated with distal radioulnar joint. Coronal FS PD FSE image.

The distal radioulnar joint is a diarthrodial trochoid articulation between the head of the ulna and the sigmoid cavity of the distal radius. The TFC consists of an articular disc and the dorsal and palmar (volar) distal radioulnar ligament. Normally, the sigmoid notch, the dorsal and volar radioulnar ligament, the interosseous membrane, and the dorsal retinaculum maintain distal radioulnar joint static stability. The palmar (volar) distal radioulnar ligament is taut in supination and the dorsal distal radioulnar ligament is taut in pronation. The pronator quadratus, the extensor carpi ulnaris, and the flexor carpi ulnaris contribute to distal radioulnar joint dynamic stability. The carpus, through its dorsal and volar radiocarpal ligament attachments, rotates the wrist radius around the ulna in pronosupination. The distal ulna moves volar to dorsal within the sigmoid notch of the distal radius between supination and pronation. There is associated translation (approximately 1 mm) of the ulna from proximal to distal. In full pronation, the distal ulna is dorsal to the proximal lunotriquetral ligament surface.

Etiology, Pathology, and Clinical Features

A distal ulnar sprain or dislocation usually occurs in the position of pronation. Pronation, extension, and radial deviation place the dorsal radioulnar, ulnotriquetral, and ulnar collateral ligaments under increased tension and may force the distal ulna to dislocate dorsally relative to the sigmoid notch. There is palmar and dorsal distal radioulnar ligament tension at both extremes of rotation (pronation and supination), and a common mechanism of injury is rotational injury with forced pronation or supination and hyperextension, as occurs in a fall on the outstretched hand. High-energy hyperextension or rotation is usually associated with fractures of the radius or ulna and ligament disruption. Traumatic distal radioulnar joint dislocations or subluxations are common. The majority of injuries represent a combination of osseous and ligamentous damage with distal radioulnar joint instability. Distal radioulnar joint instability without associated fracture injuries is usually misdiagnosed.

Pathologic examination reveals abnormal displacement of the distal radius and carpal bones relative to the ulna, but the ulna is not the mobile bone dislocating from the radius. In supination there is physiologic radius translation dorsally, and in pronation there is physiologic radius translation in a palmar direction. Disruption of sigmoid notch congruity (e.g., displacement fracture) may be seen, as may dorsal distal radioulnar ligament tears and tightening of the ulnocarpal ligament complex, which produces a destabilizing effect. Disruption of the infratendinous extensor retinaculum (the extensor carpi ulnaris subsheath) with subluxation of the extensor carpi ulnaris tendon is also found in ulnar dorsal dislocation. In Essex-Lopresti fractures there is interosseous membrane injury, dislocation or fracture of the proximal radial head, and displacement of the distal ulna dorsally and longitudinally. Ulnar dorsal dislocation is seen in hyperpronation (Fig. 10.120) with disruption of the palmar distal radioulnar ligament, ulnocarpal ligament complex injury, and dorsal infratendinous extensor retinaculum tears. There is ulnopalmar dislocation in hypersupination (Fig. 10.121), with disruption of the dorsal distal radioulnar ligament, stretching of the pronator quadratus, and distal interosseous membrane tears.

Dorsal instability of the distal radioulnar joint may also be associated with a supination deformity of the radial carpal complex. Treatment is therefore directed at correction of both the distal ulnar dorsal displacement and the supinated angulation of the carpus relative to the radius.

Clinically, patients report pain at the ulnar aspect of the wrist. Symptoms are increased in pronosupination and may be accompanied by swelling and a decrease in or loss of range of motion at the wrist. Grip weakness and the “piano key sign” (a prominent distal ulna in dorsal dislocations, Fig. 10.122), ulnar nerve dysesthesias, and an audible snap are additional clues to the diagnosis.

Classification

Distal radioulnar joint dislocations associated with acute trauma have been classified into three groups:

Type I: Dislocation of the distal radioulnar joint secondary to disruption of the primary soft-tissue structures or to osseous injury (ulnar styloid fracture).
Type II: Intra-articular distal radioulnar joint fracture-dislocations
Type III: Extra-articular distal radioulnar joint fracture-dislocations

MR Appearance

CT and MR imaging of both wrists in both full pronation and full supination have been shown to be useful in the diagnosis of distal radioulnar subluxation.⁸⁶^,⁸⁷ Another technique in the evaluation of instability at this joint uses a frame that places a calibrated degree of stress on the distal ulna and radius in conjunction with CT scanning.⁸⁸ The controlled load placed on the joint is supposed to simulate the physiologic changes in dynamic subluxation, a condition that is difficult to diagnose. Useful quantitation of the degree of subluxation may also be possible with this technique.

The advantage of MR axial imaging in maximum pronation and supination is identification of the relative positions of the distal radius and ulna with soft-tissue contrast information. Axial images display the condition of the dorsal and volar radioulnar ligaments, and volar radioulnar ligament tears may be associated with dorsal instability of the distal radioulnar joint. The normal volar distal radioulnar ligament is maximally taut when the wrist is studied in pronation. Ulnar styloid avulsions, TFC complex tears, or distal radial fractures may lead to distal radioulnar joint instability with subluxation, and these structures can be assessed during the same examination with MR imaging in the coronal plane. Compared with CT, MR imaging is more accurate in the characterization of associated effusions of the distal radioulnar joint, which are a secondary sign of TFC pathology. Axial and sagittal images are useful in demonstrating displacement of the distal ulna in relationship to the TFC complex.

FIGURE 10.120 ● (A) Dorsal subluxation of the ulna relative to the sigmoid notch. Axial color graphic. (B) Disruption of the volar margin of the TFC (volar radioulnar ligament and volar aspect of the TFC in association with a distal radius fracture). Coronal T1-weighted image. (C) Ulnar dorsal subluxation (radial volar subluxation) secondary to disruption of the volar radioulnar ligament. The extensor carpi ulnaris tendon and subsheath are also ruptured. Axial FS PD FSE image.

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Characteristic MR findings include:

Dorsal or volar (palmar) subluxation of the ulnar head relative to the sigmoid notch on axial images
Dorsal prominence of the ulna (ulna-dorsal) on sagittal images
A flattened or shallow sigmoid notch
Distal radioulnar joint diastasis on coronal images in ulnar dorsal subluxation
Massive disruption of the stabilizing capsuloligamentous structures (e.g., as in a Galeazzi fracture)
Subluxation or interposition of the extensor carpi ulnaris tendon
Associated intercalated segment instability pattern, either VISI (volar) or DISI (dorsal)
Palmar (volar) distal radioulnar ligament disruption associated with ulnar dorsal dislocation
Dorsal distal radioulnar ligament disruption associated with ulnar palmar dislocation
Ulnocarpal ligamentous complex hyperintensity (tear associated with ulnar dorsal pattern)
A tear of the dorsal infratendinous extensor retinaculum (the subsheath of the extensor carpi ulnaris, seen in ulnar dorsal dislocation)
Pronator quadratus and distal interosseous membrane hyperintensity on FS PD FSE images as part of forced hypersupination and ulnar palmar dislocation

FIGURE 10.121 ● Volar subluxation of the distal ulna (dorsal subluxation of the distal radius) with disruption of the dorsal margin of the TFC (dorsal radioulnar ligament). (A) Axial color graphic. (B) Coronal FS PD FSE image. (C, D) Axial FS PD FSE images.

FIGURE 10.122 ● (A) Ulnar dorsal dislocation in hyperpronation with torn volar radioulnar attachment. Sagittal FS PD FSE image. (B) Axial section of the distal radioulnar joint demonstrating the positions of subluxation and dislocation of the distal ulna relative to the sigmoid notch of the distal radius.

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Treatment

Delayed diagnosis is common, resulting in recurrent distal radioulnar joint instability and development of a limited range of rotation of the forearm and degenerative arthritis. Conservative treatment may be sufficient for type I or II injuries. In type I injuries (true distal radioulnar joint dislocations), reduction and immobilization may be sufficient. The treatment for type II intra-articular distal radioulnar joint fracture-dislocations is reduction and casting. Surgical treatment also depends on the type of injury. For type I injuries in which there is interposition of soft tissue (the TFC complex, extensor carpi ulnaris entrapment, osteochondral), open reduction and Kirschner wire fixation is used. In type II injuries, percutaneous Kirschner wire fixation, external fixation, or open repair is used to achieve anatomic reduction. Osteotomy or hemiresection arthroplasty may be required. Type III extra-articular distal radioulnar joint fracture-dislocations are managed with open reduction and internal fixation.

Potential complications include malunion of the distal radius and distal/dorsal subluxation of the distal ulna in type II injuries and malunion of the radius and residual distal radioulnar joint subluxation in Galeazzi fracture-dislocations.

Triangular Fibrocartilage Complex

Normal Anatomy

The TFC complex is composed of the dorsal and volar radioulnar ligaments, the ulnar collateral ligament, the meniscus homologue, the articular disc or TFC, the extensor carpi ulnaris sheath, the ulnolunate ligament, and the ulnotriquetral ligament.⁸⁹ It is classified as part of the ulnocarpal extrinsic ligamentous group and stabilizes the distal radioulnar joint and ulnocarpal articulation. The dorsal and volar radioulnar ligaments reinforce the peripheral margins of the TFC, which is thinned centrally and thickened peripherally. The thickened ulnar collateral fibers that are distal to the TFC make up the meniscus homologue. These fibers insert distally into the triquetrum, the hamate, and the base of the fifth metacarpal. The ulnolunate ligament originates on the anterior border of the TFC and inserts on the lunate. The ulnotriquetral ligament also originates on the anterior aspect of the TFC (the volar aspect of the radioulnar ligament) and extends to the volar-ulnar aspect of the triquetrum. The TFC has a biconcave morphology and articulates with the distal ulna and triquetrum in the proximal

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carpal row. With a strong radial attachment of the TFC, the ligaments that have or share TFC attachment function to connect the volar aspect of the carpus to the radius.

Triangular Fibrocartilage Complex Injuries

Triangular fibrocartilage tears represent tears of the TFC, including the central (disc) and peripheral margins. TFC complex abnormalities have been classified as either traumatic injuries (Palmer class I) or degenerative injuries (Palmer class II).⁸³ Traumatic injuries are treated by arthroscopic débridement in avascular portions and are repaired in vascularized areas.⁸⁴ Degenerative lesions of the TFC complex are treated by salvage procedures, including arthroscopic débridement, ulnar shortening, or ulnar head resection. Class I traumatic injuries of the TFC complex are further subdivided into four groups:

Class IA: Perforation or traumatic tear of the TFC disc proper (Fig. 10.123)
Class IB: Ulnar avulsion of the TFC complex with or without associated ulnar styloid fracture (Fig. 10.124)
Class IC: Distal avulsions of the TFC complex through its lunate attachment (the ulnolunate ligament) or its triquetrum attachment (the ulnotriquetral ligament) (Fig. 10.125)
Class ID: Radial avulsions at the level of the distal sigmoid notch with or without associated sigmoid notch fracture (Fig. 10.126)

FIGURE 10.123 ● Class IA lesion with slit-like tear or perforation (straight arrow) of the radial aspect of the TFC medial to its radial origin. There is communication of radiocarpal joint contrast (curved arrow) with the distal radioulnar joint. FS T1-weighted coronal arthrogram.

Class II degenerative lesions demonstrate the spectrum of ulnocarpal (ulnolunate) abutment syndrome findings and are also subdivided into several classes:

Class IIA: TFC complex wear (Fig. 10.127)
Class IIB: TFC complex wear with associated lunate and/or ulnar chondromalacia (Fig. 10.128)
Class IIC: TFC complex perforation in association with lunate or ulnar chondromalacia (Fig. 10.129)
Class IID: TFC complex perforation, lunate or ulnar chondromalacia, and lunotriquetral ligament perforation (Fig. 10.130)
Class IIE: Class IID injuries with the additional finding of ulnocarpal arthritis (Fig. 10.131)

FIGURE 10.124 ● Class IB lesion with traumatic avulsion of the ulnar attachment of the TFC. There is direct extension of contrast between the ulnar styloid and the avulsed TFC (arrow). In addition, this patient has an avulsion of the ulnar aspect of the scapholunate ligament and absent lunotriquetral ligament. FS T1-weighted coronal arthrogram.

FIGURE 10.125 ● FS sagittal T1-weighted arthrograms comparing (A) intact (black and white straight arrow) ulnocarpal (ulno-lunate and ulnotriquetral) ligament with (B) avulsed osseous insertions (curved arrow) of the ulnocarpal ligaments. There is also associated tearing of the dorsal radial aspect of the TFC. Isolated avulsion of the distal ulnolunate or ulnotriquetral ligaments as described in a class IC lesion is not common. H, hamate; T, triquetrum; tfc, triangular fibrocartilage; U, ulna; P, pisiform.

FIGURE 10.126 ● Traumatic avulsion of the radial attachment of the TFC as described in class ID lesions. Note the exposed articular cartilage at the radial sigmoid notch. Fluid communicates between the radiocarpal and distal radioulnar compartments (curved arrow) on this FS coronal T1-weighted arthrogram. The lunotriquetral ligament is absent.

FIGURE 10.127 ● Class IIA lesion with degenerative thinning (arrows) of the TFC without perforation. No lunate chondromalacia is present and the lunotriquetral ligament is intact. U, ulna. FS coronal T1-weighted arthrogram.

FIGURE 10.128 ● Class IIB lesion with degenerative fraying of the distal aspect of the TFC (straight arrow). There is chondromalacia of the lunate and triquetrum (curved arrow) without associated TFC perforation. The lunotriquetral and scapholunate ligaments are torn. FS coronal T1-weighted arthrogram.

FIGURE 10.129 ● Class IIC lesion with a central TFC perforation (straight arrow) and lunate chondromalacia (curved arrow) on a FS PD FSE coronal image. No intra-articular contrast was required to facilitate the diagnosis. The lunotriquetral ligament is intact (open arrow). Tapering of the edges of the TFC is seen in degenerative (class II) lesions, whereas traumatic (class I) tears tend to have abrupt or straight margins.

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Etiology, Pathology, and Clinical Features

The most common mechanisms in TFC complex injuries are forearm pronation, hyperextension of the wrist with rotational load, and degenerative changes (the ulnocarpal abutment syndrome). TFC tears are associated with positive ulnar variance. In general there is a higher incidence of radial-sided lesions, except that ulnar-sided tears are seen more commonly in younger patients. Asymptomatic perforations and degenerative tears are common after age 40, and traumatic tears are more common in individuals under 40 years of age.

The spectrum of pathologic changes is described above in the discussion of the Palmer classification. Microstructural changes found in the TFC include short collagen fibers in the central region in response to compression loads, superficial and deep (less organized) layers within the articular disc. An avascular radial border and central disc and mucinous or myxoid degeneration are seen in degenerative tears.

Patients with TFC pathology often present with pain, clicking, or both on the ulnar aspect of the wrist. There may be associated loss of strength, painful distal radioulnar joint rotation, catching or snapping, tenderness and pain over the TFC, and pain with stress loading of the distal radioulnar joint in pronation and supination. The “piano key sign” (dorsal-palmar ballottement of the distal ulna) is present, and there may be associated Colles', Galeazzi, and Essex-Lopresti fractures in class I injuries. An unstable flap of tissue from a TFC causes catching on the ulnar aspect of the wrist, especially when loaded in extension or ulnar deviation.

Classification

As described above, the Palmer classification divides TFC complex injuries into two classes: class I comprises traumatic tears and class II comprises degenerative tears. Bowers has proposed a classification scheme based on injuries of the distal radioulnar joint and TFC, and the Mayo classification is a treatment- and location-based system for traumatic and degenerative tear types.

Arthroscopic Evaluation

Anatomy

The TFC complex arises from the medial surface of the radius at the level of the articular cartilage. Its origin is flush with the radial articular surface, and the only way to differentiate these structures arthroscopically is by palpation with a probe. As noted earlier, the TFC complex courses toward the base of the ulnar styloid to insert onto the fovea. The articular disc is continuous with the volar ulnocarpal ligaments as well as the dorsal capsular structures. There is a strong dorsal insertion into the undersurface of the sheath of the extensor carpi ulnaris tendon. More radially, the articular disc of the TFC complex is suspended from the dorsal capsular structures of the wrist.

Pathology

When all the suspensory insertions around the periphery of the TFC complex are intact, the TFC complex is under tension and ballottement under arthroscopy produces a resiliency sometimes called the “trampoline effect.”

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Separation of the peripheral insertions of the TFC complex, especially at the fovea or radius, results in a loss of this suspensory trampoline effect.⁹⁰

FIGURE 10.130 ● FS T1-weighted coronal arthrogram demonstrating class IID injury with perforation of the TFC (straight arrow), loss of lunate articular cartilage (curved arrow), and lunotriquetral ligament disruption (open arrow). Intrasubstance enhancement of the TFC is commonly seen in degenerative lesions.

FIGURE 10.131 ● Class IIE lesion with ulnocarpal arthritis demonstrates a central TFC perforation (small straight arrows), lunate (curved arrow) and triquetral chondromalacia, lunotriquetral ligament tear (open arrow), and triquetral subchondral erosion (long straight arrow). (A) T2*-weighted coronal image. (B) FS T1-weighted coronal arthrogram.

The central portion, or centrum, of the TFC complex is thin and is the most common site of tears. The dorsal and volar portions of the TFC complex, which are thicker than the central portion, are sometimes referred to as the dorsal and volar limbi.³⁵ Whereas the thin central portion can be excised if torn, much like the meniscus of the knee, the limbi should be preserved because they appear to play an important mechanical role in the stability of the distal radioulnar joint. On average, the limbi are 4 to 5 mm thick.⁹¹ Tears of the centrum can be associated with a variety of causes. Perforations from excessive loading in patients with positive or neutral ulnar variance and ulnocarpal impingement syndromes are common. As noted earlier, these patients may present with findings indicative of cartilage degeneration of the distal ulna and medial lunate. Some patients with ulnocarpal impingement present with a triad of symptoms, including positive or neutral ulnar variance, TFC complex perforations, and lunotriquetral ligament instability. An ulnar unloading procedure, such as ulnar shortening, relieves the pressure on the lunotriquetral ligament and allows the symptoms to subside. With extreme instability or cartilage degeneration between the lunate and triquetrum, fusion of the lunotriquetral joint may be necessary in addition to the ulnar shortening.⁹¹

Studies of the vascular anatomy of the articular disc have shown that, similar to the meniscus of the knee, only the peripheral 15% to 20% of the disc is vascularized. The central portion is avascular.⁹² Therefore, although there is a potential for surgical repair of peripheral lesions, central lesions cannot be expected to heal and should be treated by excision. Reinsertion of peripheral ulnar avulsions of the TFC complex have resulted in restoration of biomechanical function and symptomatic relief.⁹⁰

The TFC is continuous with the volar ulnolunate and ulnotriquetral ligaments, and these structures provide a strong insertion into the carpus. Tears of these ligaments, implicated in ulnar wrist pain, can be depicted on MR images, and there are reports of successful treatment with arthroscopic débridement.⁹³

Magnetic Resonance Evaluation

Anatomy

Both the distal and proximal surfaces of the TFC are depicted on MR images; this information is not available with wrist arthroscopy or single-compartment radiocarpal arthrography. On coronal plane T1-weighted, T2*-weighted, STIR, or FS PD FSE images, the TFC is depicted as a biconcave disc of homogeneous low to intermediate signal intensity. The tendon of the extensor carpi ulnaris is seen on the radial aspect of the ulnar styloid process. Coronal plane images of the TFC disc demonstrate the lateral attachment to the ulnar aspect of the distal radius, with separate superior and inferior bifurcated radial attachments. The inferior radial attachment is not seen on arthroscopic evaluation restricted to the radiocarpal surface of the TFC.

The contours of the TFC (i.e., proximal and distal surfaces) and ulnar variance are best assessed on coronal images. The distribution of force across the radial plate is increased by negative ulnar variance and is reduced by positive ulnar variance. The TFC is thus an important contributor to stabilization of the medial aspect of the radiocarpal joint. Disruption of the TFC is associated with various degrees of distal radioulnar joint instability. Small volar tears lead to mild dorsal subluxation, small dorsal tears cause volar subluxation, and massive tears can produce subluxation or dislocation in either direction. Volar instability is manifested by supination and dorsal instability by pronation.

On axial images, the TFC is shaped like an equilateral triangle. The apex of the TFC complex converges on the ulnar styloid, and the base of the triangle attaches on the superior margin of the distal radial sigmoid notch. Sagittal images show the TFC in sections through the triquetrum. In this plane, the TFC morphology is discoid, as seen from anterior to posterior. The TFC is located immediately distal to the dome of the ulna and is thinned centrally with broader volar and distal margins (i.e., peripheral thickening). This peripheral thickening is composed of lamellar collagen and gives rise to the dorsal and volar radioulnar ligaments. The ulnocarpal ligament arises from the volar distal surface of the TFC and passes distally to the bones of the ulnar carpus.

Totterman and Miller⁹⁴ reported on the use of 3D gradient recall echo imaging to routinely visualize the radioulnar and ulnocarpal ligaments. The volar and dorsal radioulnar ligaments are seen as broad striated bands that originate from the volar and dorsal (respectively) radial cortices of the sigmoid notch of the distal radius and extend to the base of the ulnar styloid process. These ligaments course volar and dorsal to the central disc of the TFC (Figs. 10.132 and 10.133). The ulnolunate and lunotriquetral ligaments are directly visualized as inhomogeneous intermediate-signal-intensity structures extending from the volar aspect of the volar radioulnar ligament to the volar-ulnar aspect of the lunate and triquetrum.⁹⁴ These ligaments appear as thickenings of the capsule originating in the volar radioulnar ligament and are not as well defined as the previously described volar extrinsic ligaments on the radial side of the radiocarpal joint.

The ulnar styloid attachment of the TFC complex is secured with striated fascicles, which are extensions of the radioulnar ligament and central disc.⁹⁴ Two types of attachments to the ulna are observed. The more common is composed of two striated fascicles (Fig. 10.134); one inserts at the styloid tip and the other inserts at the base of the styloid. The low-signal-intensity striated fascicles are separated by higher-signal-intensity tissue. The less common type of TFC complex attachment is a broad-based striated attachment of fascicles along the entire length of the ulnar styloid (Fig. 10.135).

The meniscus homologue is variably demonstrated on MR images. Its low-signal-intensity pattern is best observed in its more well-defined dorsal portion. The meniscus homologue has been shown to have an insertion onto the pisiform in cadaver

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dissections and may provide stability at the level of the pisotriquetral articulation.⁹⁵ The prestyloid recess is defined as a high-signal-intensity area bordered by the meniscus homologue, the styloid attachment of the TFC complex, the central disc, the medial carpal capsule, and the extensor carpi ulnaris sheath (Fig. 10.136).

FIGURE 10.132 ● TFC complex, volar aspect. (A) Volar FS T1-weighted coronal arthrogram shows the radial attachment (arrow) of the volar radioulnar ligament (volar RUL). The ulnolunate (UL) and ulnotriquetral (UT) ligaments (components of the ulnocarpal ligament) originate and extend from the volar radioulnar ligament to attach to the volar-ulnar aspect of the lunate and triquetrum. (B) FS T1-weighted coronal arthrogram shows the ulnotriquetral ligament (UT) continuing in an ulnar distal course toward the triquetrum at the level of the volar aspect of the articular disc (d). (C) The ulnolunate (straight arrow) and ulnotriquetral (curved arrow) ligaments are visualized as a merged or confluent extension from the volar aspect of the radioulnar ligament. FS T1-weighted coronal arthrogram. (D) The lunate (L) insertion (arrows) and triquetrum insertion of the ulnolunate (UL) and ulnotriquetral (UT) ligaments, respectively, are shown. Note the broad-based common origin of these ligaments from the distal volar aspect of the volar radioulnar ligament (curved arrow). FS coronal T1-weighted arthrogram shows that the radial aspect of the TFC is torn in this patient. (E) A separate case demonstrates the continuity of the hypointense sheet of tissue representing the ulnolunate (UL) and ulnotriquetral (UT) ligaments extending from the volar aspect of the volar radioulnar ligament (curved arrow). RLT and straight arrow, radiolunotriquetral ligament; R, radius; L, lunate; U, ulna; T, triquetrum; P, pisiform; S, scaphoid.

FIGURE 10.133 ● The dorsal radioulnar ligament (dorsal RUL; arrow) attachment to the dorsal distal radius. The dorsal portions of the intrinsic interosseous scapholunate and lunotriquetral ligaments are also seen at this level. FS coronal T1-weighted arthrogram.

FIGURE 10.134 ● Insertion of the TFC complex into the ulnar styloid (s) process is accomplished by separate groups of fascicles directed to the styloid tip (white arrow) and base (black arrow). The ulnar collateral ligament (UCL), seen as a distinct structure of the TFC complex, extends from the outer aspect of the ulnar styloid to the triquetrum, hamate, and fifth metacarpal. The meniscus homologue (m) corresponds to thickening of the longitudinally oriented fibers of the ulnar collateral ligament distal to the TFC. FS coronal T1-weighted arthrogram.

FIGURE 10.135 ● Single broad-based attachment of the TFC complex extending from the tip to the base of the ulnar styloid process (arrows). FS coronal T1-weighted coronal arthrogram.

The central disc demonstrates low to intermediate signal intensity on mid-coronal images with a bowtie morphology.⁹⁴ The radial attachment of the disc is thicker than the central portion and is attached to the higher-signal-intensity hyaline articular cartilage of the sigmoid notch (Fig. 10.137). The superficial articular cartilage layer of the lunate fossa is visualized in apparent continuity with the distal surface of the radial aspect of the TFC complex disc. The proximal surface of the TFC complex central disc either is in direct contact with the increased-signal-intensity articular cartilage of the ulnar head or is separated from the articular cartilage by the ulnar extension of distal radioulnar joint fluid within the distal radioulnar compartment.

Pathology

MR imaging of the TFC complex reveals many tears that previously went undetected, including intrasubstance (i.e., horizontal) tears and peripheral lesions of the insertions of the TFC complex that do not show contrast leakage.⁹⁶ MR accuracy is reported to be 95% compared with arthrography and 89% compared with arthroscopy and arthrotomy.²³^,⁹⁶ MR imaging has also been found to be particularly valuable in assessing postoperative TFC repairs and associated distal joint instability.

Central perforations of the TFC are thought to be unusual in the first two decades of life. By the fifth decade of life, however, symptomatic perforations can be identified in 40% of TFC studies, and by the sixth decade, perforations are found in 50% of patients.¹¹^,⁹⁷ This finding may help to explain the poor correlation between clinical findings of wrist pain and communication of contrast across the TFC seen in radiocarpal arthrograms. The fact that radiocarpal compartment communication with the inferior radioulnar compartment is found more frequently in anatomic dissections than with arthroscopic injection can be explained by the existence of partial tears and unidirectional flap tears. In a cadaver study, Tan et al.⁹⁸ documented congenital perforations of the TFC in the fetus and infants, supporting the frequent finding of perforations in asymptomatic adults. These findings bring into question the significance of identifying fluid communications across the TFC in the presence of grossly normal TFC complex morphology.

On T2*-weighted images, the thin layer of hyaline articular cartilage proximal to the radial attachment of the TFC along the ulnar aspect of the distal radius demonstrates increased signal

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intensity and should not be mistaken for fluid communication with the inferior radioulnar joint or detachment of the radial aspect of the TFC. Intrasubstance degeneration of the TFC is best depicted on T2*-weighted images and appears as regions of increased signal intensity without extension to the superior or inferior margins of the TFC. The meniscus homologue demonstrates greater signal intensity than the TFC on T2*-weighted images. Partial tears in this area may be more difficult to identify due to the increased signal intensity and inhomogeneity of the meniscal homologue and ulnar attachments. Tears of the TFC may occur either as an isolated injury or in association with subluxations of the distal radioulnar joint or perilunate dislocations. TFC tears, demonstrated by discontinuity or fragmentation, are most commonly located near or adjacent to the radial attachment.⁶⁷ Contour irregularities, especially with associated regions of increased signal intensity, can be identified on T1-weighted, FS PD FSE, and T2*-weighted images. Tears on the radial aspect of the TFC frequently have a dorsal-to-volar orientation and extend to both its proximal and distal surfaces (Fig. 10.138).

FIGURE 10.136 ● Meniscus homologue and prestyloid recess. (A) The triangular meniscus homologue (m) and prestyloid recess (p) are shown on an FS coronal T1-weighted arthrogram. The prestyloid recess is seen proximal to the meniscus homologue and distal to the ulnar styloid attachment of the TFC complex. The TFC, or central disc, is located radial to the prestyloid recess, whereas the medial capsule defines the ulnar aspect of the recess. The extensor carpi ulnaris tendon sheath courses dorsal to the prestyloid recess. (B) A more dorsal coronal image demonstrates the confluence of the meniscus homologue (m) and the radial origin of the dorsal radioulnar ligament (large arrow). A fold from the dorsal radioulnar ligament forms the proximal attachment of the TFC complex (small arrow). FS coronal T1-weighted arthrogram.

FIGURE 10.137 ● The TFC. (A) The distal aspect of the TFC or central disc is shown to be contiguous with the articular cartilage of the distal surface of the lunate fossa (small black arrows). The volar and dorsal radioulnar ligaments contribute to the striated tissue between the ulnar styloid and the central disc. High-signal-intensity articular cartilage (large white arrow) is present at the radial attachment of the central disc to the sigmoid notch of the radius. The central disc is in direct contact with the articular cartilage of the ulnar head in the absence of distal radioulnar joint fluid distention (small white arrow). FS coronal T1-weighted arthrogram. (B) The extensor carpi ulnaris tendon and sheath (extensor carpi ulnaris) are identified on a more dorsal coronal image in the plane of the TFC. The TFC attaches to the sheath of the extensor carpi ulnaris tendon dorsomedially. FS coronal T1-weighted arthrogram.

Associated synovitis, seen as a localized fluid collection or radiocarpal joint effusion on FS PD FSE or T2*-weighted images, may be associated with chondromalacia of the lunate, triquetrum, or ulna. In younger patients, there is a higher incidence of tears on the ulnar aspect of the TFC. Peripheral tears are secondary to traumatic avulsion, whereas central perforations may be associated with findings of TFC degeneration.²⁴ These degenerative changes, usually histologic mucinous or myxoid degeneration, are seen as increased signal intensity on T1- and T2*-weighted images and thinning or attenuation of the articular disc. Degeneration is common in the thinner central portion of the TFC disc and initially occurs on the ulnar or proximal surface of the TFC.⁶⁶ Whereas deformity of the TFC is common in patients with negative ulnar variance, TFC tears are associated with positive ulnar variance.

In summary, key findings include:

Intrasubstance degeneration, best visualized on T1-, PD-, or T2*-weighted gradient-echo images
Volar margin tears associated with dorsal subluxation of the ulna relative to the radius
Dorsal tears associated with volar subluxation of the ulna
Volar instability seen on supination in the axial plane
Dorsal instability seen on pronation in the axial plane
Radial-sided tears with a dorsal-to-volar orientation
Ulnar avulsion with or without an ulnar styloid fracture
Radial avulsion with or without a sigmoid notch fracture
Chondromalacia and sclerosis of the lunate, triquetrum, and distal ulna in ulnocarpal (ulnolunate) abutment syndrome with loss of the normal signal intensity of articular cartilage

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Contour irregularity of the proximal (undersurface) or distal surfaces in partial tears
Fluid extension across the articular disc or discontinuity
Synovitis

FIGURE 10.138 ● Comparison of (A) an intact TFC with (B) a TFC tear on FS sagittal T1-weighted arthrograms. The TFC tear (curved arrow) involves the radial aspect of the disc without disruption of the volar ulnocarpal ligaments (straight arrow). H, hamate; T, triquetrum; tfc, triangular fibrocartilage; P, pisiform; U, ulna.

FS PD FSE sequences allow improved definition of the proximal and distal surfaces, and T2* gradient-echo sequences allow improved visualization of intrasubstance degeneration and tears. MR arthrography, performed with radiocarpal injection, is useful in the differentiation of severe degeneration from partial tears.

Treatment

The significance of TFC complex lesions must be evaluated as a part of the whole clinical presentation. As noted earlier, asymptomatic tears become more common after 40 years of age.¹¹ In many cases, a TFC complex lesion is not actually responsible for the patient's symptoms but is rather a clue to the pathologic process. In these cases, treatment modalities are not directed at the TFC complex tear itself, but at the underlying pathology. For example, in the patient with positive ulnar variance and a TFC complex tear, treatment is aimed at relieving the overloading of the distal ulna rather than merely repairing or débriding the tear.

Conservative treatment includes activity modification and anti-inflammatory medications. Surgical treatment approaches vary, depending in part on the classification of the injury. As mentioned earlier, traumatic Palmer class I injuries are subdivided into four types: central perforations (Palmer class IA) (Fig. 10.139); ulnar avulsion and distal ulnar fractures (Palmer class IB); distal avulsions (Palmer class IC); and radial avulsion (Fig. 10.140) and sigmoid notch fractures (Palmer class ID). Palmer class II injuries are degenerative (also known as the ulnocarpal/ulnolunate abutment syndrome) and are subdivided into five types: TFC complex wear (degeneration) (Palmer class IIA (Fig. 10.141); TFC complex wear with lunate, triquetral, and possibly ulnar chondromalacia (Palmer class IIB); TFC complex perforation with lunate, triquetral, and ulnar chondromalacia (Palmer class IIC); TFC complex perforation with lunate, triquetral, and ulnar chondromalacia and lunotriquetral ligament perforations (Palmer class IID) (Fig. 10.142); and TFC complex perforation with lunate, triquetral, and ulnar chondromalacia and lunotriquetral ligament tear and ulnocarpal arthritis (Palmer class IIE) (Fig. 10.143). Surgical procedures include débridement and repair of a tear, resection and débridement of a flap tear, and augmentation if repair is not possible. Reconstruction often produces

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better long-term results than resection. In triquetral impingement of the ulnar styloid, limited ulnar styloidectomy may provide symptom relief.

FIGURE 10.139 ● (A) Central perforation of the TFC on a coronal color illustration with a sagittal inset. (B) Central TFC perforation on an FS PD FSE image.

FIGURE 10.140 ● (A) Radial avulsion of the TFC on coronal color illustration. (B) Vertical radial-sided TFC tear parallel to the normal radial chondral junction. Coronal FS PD FSE image.

FIGURE 10.141 ● Palmer class II degenerative wear as the initial stage of ulnocarpal (ulnolunate) abutment syndrome. Color coronal illustration.

TFC complex resection and débridement are the treatments of choice for a flap tear of the TFC complex, similar to that of the meniscus of the knee, that causes pain. These treatments also are indicated if there is instability of the distal radioulnar joint due to the TFC complex injury. If repair is not possible, then the structure should be augmented. We use an intra-articular ligament reconstruction to augment tears of the dorsal limbus of the TFC complex that lead to distal radioulnar joint instability. There are data, however, that indicate that no resection of the TFC complex is mechanically benign, even though the avascular, thin centrum of the disc was thought by many to be mechanically insignificant, and the mechanics for stabilizing the distal radioulnar joint were thought to be primarily derived from the intact dorsal and volar limbi. Adams⁹⁹ has reported that although the dorsal and volar limbi of the TFC complex provide the final restraints to distal radioulnar joint dislocation, the centrum is an important component for normal motion. Resection of the centrum was found to alter the mechanics of the distal radioulnar joint and the remainder of the TFC complex.⁹⁹ These findings suggest that the TFC complex should not be resected with impunity and the methods of reconstruction need to be studied more carefully.

The meniscus homologue consists of a fold of fibrous tissue interposed between the tip of the ulnar styloid and the triquetrum. This is an evolutionary remnant of the early primate wrist, in which weightbearing was facilitated by an elongated ulnar styloid that articulated, through a free meniscus, with the triquetrum.¹⁰⁰ Occasionally, a free meniscus or an abnormally long ulnar styloid tipped with articular cartilage that impinges against the triquetrum can be seen in humans. Triquetral impingement of the ulnar styloid results in cartilage degeneration of the triquetrum. This impingement can be treated with a limited ulnar styloidectomy. The meniscus homologue forms the entrance to the prestyloid recess seen in arthrographic examination of the wrist.

Fractures about the Wrist

Conventional radiography is limited in the detection of nondisplaced or partially displaced fractures of the carpus and distal

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radius. Trispiral tomography depends on correct planar positioning, or carpal fractures may be underdiagnosed. Results from early bone scintigraphy, performed within 72 hours of an acute fracture, may be negative or equivocal. CT using thin (1.5-mm) sections in either direct coronal or axial planes with reformatting and 3D rendering is the most accurate modality for identifying fractures and for characterizing morphology and associated comminution or displacement. Chip fractures can be detected by CT in patients with negative findings on MR studies. Fracture extent and adjacent marrow hyperemia are clearly demonstrated on MR images. In subacute and chronic fractures, sclerosis demonstrates low signal intensity on T1-weighted images. The temporal stage of a fracture (e.g., acute, subacute, chronic) and its location determine the optimal diagnostic imaging plane (e.g., coronal, axial, or sagittal). MR imaging shows associated ligamentous injury in isolated or multiple carpal bone trauma. If initial imaging is inadequate, delayed diagnosis and treatment may lead to poor anatomic reduction and loss of function.

FIGURE 10.142 ● Palmer class II degenerative TFC tear in association with proximal lunate chondral erosion and lunotriquetral (LT) ligament tear. Coronal FS PD FSE image.

FIGURE 10.143 ● Advanced changes of ulnocarpal (ulnolunate) abutment (Palmer class II) with TFC tear, lunate, triquetral and ulnar chondromalacia, and lunotriquetral ligament tear. Coronal color illustration.

Distal Radius Fractures

Distal radius fractures are among the most common skeletal injuries, representing about one sixth of all fractures seen in the acute setting. They occur in all age groups, from young males, in whom they are usually high-energy injuries to older females with osteoporosis, in whom they are low-energy injuries. The majority are articular, with disruption of the radiocarpal and distal radioulnar joints.

Distal radius fractures are most commonly seen at the scaphoid fossa, the lunate fossa, and the sigmoid notch at the distal radioulnar joint. They include:

Intra- and extraarticular fractures of the distal radius, including Barton's fracture, an intra-articular fracture-dislocation or subluxation (a palmar or dorsal fracture) with displacement of the carpus
Colles' fracture, a fracture of the distal metaphysis with dorsal displacement, angulation (silver fork deformity), radial angulation, and radial shortening
Smith's fracture (reverse Colles'), a palmarly angulated fracture (the garden spade deformity)

Etiology, Pathology, Classification, and Clinical Features

The distal radius is frequently fractured in a fall onto the outstretched hand. In osteoporosis these fractures may be low-energy injuries. The mechanisms of injury include dorsiflexion and hyperextension, tension along the palmar surface of the wrist, and compression and comminution of the dorsal surface. The weaker dorsal cortex is associated with extra-articular metaphyseal fracture in older individuals. In younger patients greater longitudinal compression forces result in intra-articular fracture and displacement.

There are several systems for classifying fractures of the distal radius:¹⁰¹

The Frykman classification¹⁰² (Fig. 10.144) has received the most attention. This system differentiates among fractures based on whether they are intraarticular or extra-articular and on the degree to which they involve the distal radioulnar joint.
In another system, developed by Melone,¹⁰³ articular fractures of the distal radius are classified into five fracture types based on the degree and direction of displacement of the articular fragments (Fig. 10.145) and indications

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for open reduction. The four basic components of articular fractures in this classification are divided into metaphyseal or shaft, radial styloid, dorsal medial, and palmar medial sections. This system is clinically useful because it indicates when open reduction is necessary to achieve accurate anatomic reduction. On routine lateral radiographs, the normal palmar tilt of the articular surface of the distal radius is 10° to 14°. On PA radiographs, the inclination of the radial articular surface forms an angle of 23° with the long axis of the forearm. These angles must be accurately restored with fracture reduction. If the palmar tilt is not anatomically correct, the range of motion in flexion will be limited and an intercalated instability pattern of the carpus may develop. Loss of the angle of inclination leads to increased loading of the radial articular surface and arthritic degeneration.¹⁰⁴
A universal classification that has replaced the Frykman classification, including the treatment algorithm. This classification is based on location, displacement, stability, and reducibility. Extra-articular and intra-articular fractures are subdivided into nondisplaced and displaced fractures.
The Mayo classification, which considers the scaphoid, lunate, and sigmoid notch as separate articulations with involvement of one or more articular fossae

FIGURE 10.144 ● Nondisplaced intraarticular distal radius fracture (Frykman type III) associated with scapholunate ligament tear, hook of the hamate fracture, and nondisplaced fracture of the distal scaphoid pole. Fracture-related marrow edema is hyperintense on both FS PD FSE (A) and fast STIR (B) coronal images. The dorsal-to-volar extension of the fracture is shown on a T1-weighted axial image (C). In the Frykman classification of distal radius fractures, intra-articular fractures are classified as class III or higher, based on radiocarpal, distal radioulnar joint, and distal ulnar involvement. Complex intra-articular fractures have a poor prognosis.

FIGURE 10.145 ● The Melone classification of distal radius articular fractures. The displacement of the medial complex (which consists of medial fragments and ligamentous attachments to the ulnar styloid and carpus) is the basis for classifying four types of articular fractures. (1) In a type I fracture, the medial complex may be displaced or not, with stable reduction and congruity of the joint surface. (2) In a type II fracture, there is comminution and the fracture is unstable. The medial complex is posteriorly or anteriorly displaced. (3) In a type III fracture, the medial complex is displaced and there is a spike fragment from the comminuted radial shaft. (4) In a type IV fracture, separation or rotation of the dorsal and palmar medial fragments occurs, with severe disruption of the distal radial articular surface. Small and large curved arrows indicate rotation of distal and palmar medial fragments; D, dorsal; d, dorsal medial fragment; p, palmar medial fragment; V, volar.

FIGURE 10.146 ● (A) Dorsal displacement of the distal radius in a Colles' fracture resulting from a fall on an outstretched hand. Lateral view color illustration. (B) Nondisplaced transverse Colles' fracture proximal to the distal articular surface of the radius. Coronal T1-weighted image.

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Clinically, patients present with pain and deformity at the distal radius, with swelling of the dorsum of the hand and wrist with ecchymosis. The hand is dorsally displaced in a Colles' fracture or palmarly displaced in a Smith's fracture.

Colles' Fractures

Colles' fractures (Fig. 10.146) occur secondary to a fall on the outstretched hand, with a pronated forearm in dorsiflexion. The fracture commonly occurs in the distal metaphysis of the radius in women older than 50 years of age. The fracture line occurs within 2 to 3 cm of the articular surface of the distal radius. The distal fracture segment may demonstrate dorsal displacement, angulation, or both. There may also be medial or lateral displacement. The transmission of force across the transverse carpal ligament may result in an associated ulnar styloid fracture. There may also be associated distal radiocarpal or radioulnar joint involvement.

Smith's Fractures

Smith's fracture, a reverse Colles' fracture, is extra- or intra-articular palmarly angulated fracture with palmar displacement of the hand and wrist.

Barton's Fractures

Barton's fractures are intra-articular (rim) fracture-dislocations of the distal radius. Dislocation is a primary feature, and they may be displaced dorsally or palmarly with the carpus.

Intra-Articular Fractures

Intra-articular fractures are classified according to the Melone system based on injury to the medial complex at the level of the lunate fossa. In this system there are five fracture types and four fracture components (radial shaft, radial styloid, dorsal-medial, and volar-medial fragments). Specific fracture types have the following characteristics:

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Type I: Minimally displaced (Fig. 10.147)
Type II fractures. Type II, or die-punch, fractures are subdivided into two groups:
Type IIA: Dorsally displaced (most common) or volarly displaced (Figs. 10.148 and 10.149)
Type IIB: Die-punch fractures with lunate impaction, most commonly on the dorsal medial component. There is greater communication and displacement of the medial fragments, usually in a dorsal direction. A double die-punch fracture occurs when both the scaphoid and lunate impact the articular surface of the distal radius. Articular offset of the radiocarpal joint may exceed 2 mm.
Type III: Addition of a spike fragment from the volar metaphysis (Fig. 10.150)
Type IV: Separation or rotation of the dorsal and palmar medial fragments and disruption of the distal radius articulation (Fig. 10.151)
Type V: Explosion fracture with comminution from the articular surfaces to the diaphysis (Fig. 10.152)

MR Appearance

Coronal images are used to appreciate all component articular fragments on one or two images as well as associated intrinsic ligament and TFC pathology. Sagittal images are required to accurately assess volar or dorsal displacement of the key medial fragments of the lunate fossa. Specific findings include:

Fracture diastasis can be directly measured on coronal, axial, or sagittal images.
Involvement of scaphoid plus lunate fossa can be evaluated on coronal images.
Fracture line(s) with extension to the volar or dorsal distal radius
Articular involvement should be correlated with offset of the chondral surface and subchondral plate.
Associated injury of the radial shaft and styloid
Marrow edema associated with carpal fractures or radial impaction and joint effusion
Synovitis and subcutaneous edema
Associated partial or complete ligament tears

Treatment

Treatment is based on whether there is a stable or unstable reduction and the presence or absence of associated distal radioulnar joint instability, median nerve dysfunction and carpal tunnel syndrome, tendon and carpal injury, and radiocarpal

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arthrosis (associated with articular surface incongruity of more than 2 mm). Conservative treatment is appropriate for stable (Melone type I) injuries. Surgery is necessary for more complex injuries, and treatment considerations include the following:

Melone type IIA (unstable dorsal or volar displacement): treatment with reduction and external fixation
Melone type IIB: not reducible by closed techniques, treatment with open reduction and internal fixation (ORIF)
Melone type III: treatment with ORIF; volar spike fragment from metaphysis places adjacent nerves and tendons at risk
Melone type IV: arthroscopic percutaneous reduction and pinning or ORIF

FIGURE 10.147 ● (A) Intra-articular nondisplaced radius fracture without separation of the medial complex (lunate fossa and related soft-tissue components). Coronal FS PD FSE image. (B) Intact lunate fossa is demonstrated on this sagittal T1-weighted image.

FIGURE 10.148 ● (A) A type II articular fracture with die-punch impaction of the dorsal medial component. Color coronal illustration. (B) Dorsal coronal FS PD FSE image demonstrating selective fracture extension of the dorsal lip of the lunate fossa on this coronal FS PD FSE image. (C) Dorsal die-punch involvement of the lunate fossa on a T1-weighted sagittal image.

FIGURE 10.149 ● (A) Displaced die-punch fracture of the lunate fossa. Coronal color illustration. (B) Greater comminution of the dorsal metaphysis with dorsal tilting and shortening of the radius. T1-weighted sagittal image.

FIGURE 10.150 ● (A) Type III spike fractures include the articular disruption seen in a type II injury with the addition of a volar metaphyseal spike fragment. Displacement of the volar spike fragment may result in injury to adjacent nerves and tendons. Coronal color illustration. (B) Volar spike fragment on sagittal T1-weighted image.

FIGURE 10.151 ● (A) Type IV fracture pattern with wide separation on rotation of the dorsal and palmar medial fragments. Coronal color illustration. (B) Coronal T1-weighted image shows splitting and depression of the lunate fossa (small white arrows) of the distal radius, with proximal migration of the lunate (black arrow). Associated diastasis (large white arrow) of the distal radioulnar joint is present, with complete disruption of the TFC complex.

FIGURE 10.152 ● Type V explosion fraction with comminution extending from the distal radius articular surfaces to the diaphysis. This injury pattern is associated with massive soft-tissue trauma. Coronal color illustration.

Ulnar Styloid Fractures

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Ulnar styloid fractures, which may occur as isolated injuries or in association with distal radius fractures, include distal avulsion (articular fractures), ulnar base fractures, midstyloid fractures, and fractures of the tip of the styloid (avulsion by the ulnar collateral ligament complex). They occur with class I traumatic ulnar avulsion injuries of the TFC complex, and the best indication of the diagnosis is a transverse fracture line in the ulnar styloid. They tend to occur in older women, with the peak age being 60 to 80 years. Ulnar-sided TFC lesions are more common in a younger population.

Etiology, Pathology, and Clinical Features

Ulnar styloid fractures frequently occur after a fall on the outstretched hand. Distal radius fractures are among the most common skeletal injuries, representing 74% of forearm fractures, and there are associated ulnar styloid fractures in 61% of cases. They may occur as a subtype of traumatic TFC complex tears and are found in association with over 50% of Colles' fractures.

On pathologic examination there is usually disruption of the TFC medially (the ulnar aspect) and evidence of a styloid fracture either at the tip, midway from the base to the tip, or at the base. Fracture of the tip (Fig. 10.153) is caused by styloid-carpal impaction, and avulsion may be associated with an intact periosteal sleeve. Fracture of the base (Fig. 10.154) is associated with avulsion of the TFC styloid attachment or avulsion of the foveal attachment (proximal to the styloid tip), resulting in destabilization of the ulnar attachment of the TFC complex. As mentioned, ulnar styloid fractures are frequently found with distal radius articular fractures, and the extensor carpi ulnaris subsheath may be avulsed or stripped adjacent to the styloid.

The most common clinical sign is ulnar pain, with point tenderness, swelling, and a restricted range of motion. Base fractures are associated with wrist instability involving the radiocarpal joint and the distal radioulnar joint (when fracture displacement is more than 3 mm). The patient may report an associated Colles' fracture or Essex-Lopresti fracture or fracture-dislocation of the radial head and interosseous membrane disruption with dislocation of the distal radioulnar joint.

Classification

In addition to the Melone classification of distal radius fractures (described earlier), ulnar styloid fractures are classified according to TFC complex abnormalities and nonunion. Class I traumatic TFC complex abnormalities (not associated with class II degenerative tears) may be central perforations (Palmer class IA), ulnar avulsions (Palmer class IB) with or without distal ulnar fractures, distal avulsion (Palmer class ID), or radial avulsion (Palmer class D) with or without sigmoid notch fracture. Ulnar styloid nonunions are classified as either type 1 (distal styloid fracture) or type 2 (fracture of the base of the styloid).

MR Appearance

The coronal plane is useful in identifying proximal or distal fracture location and the relationship of the ulnar styloid to the ulnar-sided TFC attachments:

Hypointense or hyperintense fracture line
Marrow edema proximal and distal to the fracture site
Displacement of fragments
Associated traumatic avulsion of the TFC at its insertion at the base of the ulnar styloid
Distal radioulnar joint instability, most likely to be seen with base fractures, with interosseous membrane tears and fluid interposed between the TFC and the attachment to the styloid base
Associated distal radius articular fractures (the ulnar styloid is part of the medial complex)

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Associated soft-tissue injury, including the ulnar collateral ligament of the wrist, the TFC complex, and tendon injuries (e.g., extensor carpi ulnaris)

FIGURE 10.153 ● (A) Type 1 ulnar styloid fracture nonunion with intact TFC complex. (B) Ulnar styloid nonunion distal to the attachment of the TFC. Coronal T2* gradient-echo image.

FIGURE 10.154 ● (A) Ulnar styloid fracture at the base of the styloid associated with an unstable distal radioulnar joint. Nonunion of ulnar styloid base on coronal T1-weighted (B) and coronal FS PD FSE (C) images. The TFC and ulnocarpal ligaments are attached to the styloid fragment.

Treatment

Isolated ulnar styloid tip fractures are usually clinically insignificant. Displaced fractures of the ulnar styloid base, which are usually associated with ligamentous and TFC tears and distal radioulnar joint instability, are at risk for nonunion. The rate of nonunion is approximately 25%, and it is classified as either type 1, associated with a stable distal radioulnar joint (the TFC insertion is intact),³⁰ or type 2, associated with an unstable distal radioulnar joint. Conservative treatment (closed reduction and immobilization) is appropriate for isolated ulnar styloid tip fractures and nondisplaced fractures of the base of the styloid with a stable distal radioulnar joint. Surgical treatment, however, is required for nondisplaced base fractures with an unstable distal radioulnar joint (open repair) and for base fractures with more than 2 mm of displacement or associated severe ligamentous or TFC injuries (open reduction).

Carpal Fractures

Scaphoid Fractures

Scaphoid fractures are the most common fractures of the carpus.¹⁰⁵ They may appear in any age group from the young to the elderly but are most common in adolescents and young male athletes. The scaphoid is the largest and most radial bone in the proximal row. The proximal surface is biconvex, for articula-tion with the radius, and the distal surface is convex, for articulation with the trapezium and trapezoid. The dorsal surface is

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the attachment site for the dorsal radiocarpal and radial collateral ligaments. There is a palmar (volar) surface concavity which contains the radioscaphocapitate ligament. The flexor retinaculum attaches to the scaphoid tubercle, and the medial surface has two facets, a semilunar surface for lunate articulation and a large concavity for capitate articulation. The vascular supply is provided by the radial artery. Dorsal ridge vessels supply the proximal 70% to 80% of the scaphoid and scaphoid tubercle branches supply the distal 20% to 30%. The absence of a separate proximal pole blood supply leads to a propensity for delayed healing and AVN of the proximal pole (see the discussion of AVN and nonunion of the scaphoid, below).

Etiology, Pathology, and Clinical Features

Fractures of the scaphoid are frequently associated with dorsiflexion loading and a radial deviation mechanism, such as might occur in a protective maneuver in a fall with the arm outstretched. Forceful extension (hyperextension) and radial deviation maximize forces across the scaphoid. Fractures may involve the tuberosity (the distal volar prominence), the distal third, the waist (the middle third), or the proximal pole. Tuberosity and distal articular surface fractures are usually smaller than distal third, middle third, or proximal pole fractures. They may be horizontal oblique, vertical oblique, or transverse. Scaphoid waist fractures are considered stable if they are noncomminuted and perpendicular to the long axis of the scaphoid. Increased obliquity, dorsal comminution, and displacement all indicate instability. With distal osteochondral fractures there is often a bone flake. Bone failure is often initiated at the palmar (volar) cortex.

The patient presents with pain over the anatomic snuffbox, weakness, a limited range of motion, and decreased grip strength. Pain is often exacerbated by radial deviation and flexion. There may be a history of participation in contact sports, a fall, or an accident, and delayed diagnosis is common.

Imaging Evaluation and MR Appearance

A conventional radiographic diagnostic series includes PA, ulnar deviation, oblique, and lateral radiographs. Repeat studies after a 2- to 3-week delay may be necessary if plain film radiographs are negative. Negative bone scintigraphy findings may require repeat studies 48 hours after the initial injury. MR may demonstrate trabecular edema prior to a defined cortical bone fracture (Fig. 10.155).

On MR imaging studies of scaphoid fractures, the usually hypointense fracture line is clearly displayed and may persist, contrasting with the surrounding hyperintensity of marrow during healing (Fig. 10.156). The identification of extension to cortical bone is necessary to accurately differentiate acute from chronic fractures, and it allows MR imaging to be more sensitive than CT or conventional radiography in evaluating the progress of subacute or chronic fractures.

Sagittal images demonstrate the abnormal morphology of the scaphoid, secondary to fracture fragmentation or suboptimal healing (i.e., humpback deformity). This foreshortening of the scaphoid is associated with DISI instability (Fig. 10.157).¹⁰⁶ The presence of Herbert screws produces minimal artifact. The articular cartilage surface of the scaphoid and congruity of adjacent coronal surfaces should be assessed. T2*-weighted images are not as sensitive to the range of contrast as conventional T1-weighted images and may not identify a nonacute, nondisplaced fracture. Gradient-echo images are, however, useful in demonstrating the integrity of the adjacent scapholunate ligament and loss of the normal trabecular pattern (marrow edema is diminished relative to the fracture line). The volar capsule (the radioscaphocapitate ligament and radiolunotriquetral ligament) is shown on sagittal images, and adjacent synovitis or edema of ligamentous structures may be identified on T1- or T2*-weighted images at the level of the scaphoid. STIR or FS PD FSE sequences are more sensitive to hyperemia (in the proximal pole or in the bone adjacent to the fracture site), which may be misdiagnosed as sclerosis, end-stage necrosis, or both on conventional T1-, T2- (FS PD FSE), or T2*-weighted images. Contrast-enhanced imaging may be necessary to document viability of the proximal pole.

FIGURE 10.155 ● Initial presentation of transverse scaphoid fracture without interruption of the scaphoid cortex. Coronal FS PD FSE image.

Characteristic MR findings include:

Fracture line, in 80% of cases in the scaphoid waist (middle third) (Fig. 10.158), in 10% of cases in the proximal pole, and in 10% of cases in the tuberosity or distal pole (Fig. 10.159)
Scaphoid flexion (humpback deformity) on sagittal images (Fig. 10.160)
Intercarpal instability (ISI), especially if there is a scaphoid flexion deformity without injury to the scapholunate ligament (Fig. 10.161) with resultant wrist shortening
Fracture extension to the cortex differentiates acute from chronic fractures (intact cortex implies a chronic process) (Fig. 10.162).
Scaphoid angulation (the scaphoid is hinged open dorsally on the intact volar radioscaphocapitate ligament in association with dorsiflexion instability of the lunate)

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Subchondral marrow edema adjacent to or on both sides of the fracture (see Fig. 10.160)
Diffuse marrow edema within scaphoid (less common)
Proximal pole edema or edema on either side of the fracture site
Associated injury to the scapholunate ligament and volar capsule (radioscaphocapitate and radiolunotriquetral ligaments)
Displaced and unstable fractures have a greater-than-1-mm step-off or an increased capitolunate angle (more than 30°).
Instability from uncorrected displacement is associated with pseudarthrosis.
AVN in the proximal pole as a complication of scaphoid fracture
Early SLAC with chondral loss between the distal pole of the scaphoid and the distal radius (styloid).

FIGURE 10.156 ● (A) T1-weighted coronal image shows a hypointense healing fracture line located across the proximal pole of the scaphoid (black arrows), with intact cortical margins (white arrows). Normal fatty marrow is present in the proximal pole. (B) Corresponding axial CT does not show cortical or trabecular fracture. This is consistent with the continuity of the cortex seen on corresponding MR images, which are more sensitive in the initial and healing stages of scaphoid fractures. Small chip fractures of other carpal bones, however, are still best evaluated with thin-section CT.

FIGURE 10.157 ● Scaphoid fracture with DISI. (A) A 3D CT rendering of the foreshortened scaphoid (curved arrows) is displayed on a 2D CT reformatted background. (B) A T1-weighted sagittal image illustrates the humpback scaphoid deformity characterized by flexion of the distal pole (curved arrow) relative to the fracture line (straight arrow) and proximal pole. The radioscaphocapitate ligament is not seen, and there is localized synovitis in its expected location. (C) A T1-weighted sagittal image demonstrates DISI secondary to the humpback deformity, and wrist shortening without scapholunate interosseous ligament tear. The dorsal tilt of the lunate (curved arrow) and increased capitolunate angle (double-headed arrow) are indicated. The capitate is dorsally displaced relative to the radius, as is characteristically seen in DISI instabilities. D, dorsal; V, volar.

FIGURE 10.158 ● Middle-third scaphoid waist fracture. The scaphoid is unique in its relationship to the distal radius, distal carpal row, and volar carpal ligaments and is more susceptible to injury than the other carpal bones. Coronal color illustration.

FIGURE 10.159 ● Distal-pole scaphoid fracture. Distal-pole scaphoid fractures are more commonly seen in children. (A) Coronal T1-weighted image. (B) Coronal FS PD FSE image.

FIGURE 10.160 ● (A) Marrow edema on both proximal and distal sides of a scaphoid fracture. Coronal color illustration. Coronal T1-weighted (B) and FS PD FSE (C) images with hypointense fracture line associated with adjacent marrow edema, which is hypointense on the T1-weighted image and hyperintense on the FS PD FSE image.

Treatment

Fractures with a gap of 1 mm or less of diastasis are considered stable. Although certain types of scaphoid fractures (classified as type B fractures) have an increased rate of complications with nonoperative treatment, in fact all complete scaphoid fractures are potentially unstable, even in the absence of any displacement on initial evaluation.¹⁰⁷ Incomplete and tubercle fractures of the scaphoid have a good prognosis with nonoperative treatment, and the union rate for uncomplicated fractures is as high as 95%. Unstable scaphoid fractures, however, may have a nonunion rate of up to 50% with closed treatment. Seventy percent of scaphoid fractures involve the middle third, or waist, of the scaphoid, and these fractures have an increased risk for delayed union and AVN (20% of cases).¹⁰⁸ Twenty percent of scaphoid fractures involve the proximal third of the scaphoid (with a 14% to 39% risk of AVN), and 10% involve the distal third. The blood supply of the scaphoid is primarily through the distal pole, entering

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via the dorsal ridge from branches of the radial artery. Thus, with fractures through the waist of the scaphoid, blood supply to the proximal pole is poor, accounting for the high rate of AVN and delayed healing (see more detailed discussion on AVN and nonunion of the scaphoid below). Associated injuries such as scapholunate dissociation and capitate head shear fracture and triquetral fracture also affect healing. Other complications of scaphoid fractures include deformity (including the humpback deformity), carpal instability (DISI), secondary osteoarthritis and other degenerative changes, carpal tunnel syndrome, sympathetic dystrophy, and pseudoarthrosis at the fracture site.

FIGURE 10.161 ● Scaphoid flexion on color sagittal illustration (A) and T1-weighted sagittal image (B). (C) The dorsal fibers of the scapholunate ligament are intact, as shown on this coronal FS PD FSE image.

Conservative treatment includes immobilization and cast application. Surgery may include internal fixation for displaced fractures and Herbert screws for interfragmentary compression (Fig. 10.163). There is a 92% success rate with Kirschner wires. Silicone synovitis may result after the use of Silastic implants (Fig. 10.164).

Unstable Scaphoid Fracture-DIslocations

Wrist dislocations have varying degrees of perilunar instability (PLI). The degree of PLI is divided into four stages (Fig. 10.165) based on the degree of carpal dislocation and ligamentous injury that starts at the scapholunate joint (Fig. 10.166) and progresses around the lunate. The four stages of PLI are:

Stage I: Scaphoid dislocation or instability with scapholunate interosseous and radioscaphoid ligament injury
Stage II: Capitate dislocation and opening of the space of Poirier

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Stage III: Triquetral dislocation and radiotriquetral ligament failure
Stage IV: Radiocapitate, radiotriquetral, and dorsal radiocarpal ligament failure with lunate dislocation

FIGURE 10.162 ● Subacute scaphoid fracture without discontinuity of cortical margins. Coronal T1-weighted image.

FIGURE 10.163 ● Internal fixation of proximal pole scaphoid fracture. Smooth Kirschner (K) wire fixation or Herbert's screw techniques have been used. Bone grafting is used for nonunions and comminuted fractures. (A) Coronal T1-weighted image. (B) Sagittal FS PD FSE image.

FIGURE 10.164 ● Silastic implant of the proximal pole of the scaphoid. Silicone synovitis may complicate this type of implant replacement arthroplasty. Coronal T2* gradient-echo image.

FIGURE 10.165 ● Perilunate patterns of instability. Stage I is scapholunate failure, stage II is capitolunate failure, stage III is triquetrolunate failure (with triquetral dislocation and radiotriquetral ligament failure), and stage IV is dorsal radiocarpal ligament failure resulting in volar rotation of the lunate. Color coronal color illustrations.

In most carpal dislocations or fracture-dislocations the scaphoid either fractures or dislocates from the lunate. PLI is thus progressive and may occur secondary to an impact on the thenar side of the wrist producing hyperextension, ulnar deviation, and intercarpal supination.

After scapholunate dissociation (stage I PLI), further hyperextension force is associated with tears of the radioscaphocapitate ligament or an avulsion fracture of the radial styloid and dorsal dislocation of the capitate relative to the lunate (stage II PLI). With further hyperextension and intercarpal supination, tears occur in the dorsal and volar radiotriquetral ligaments (stage III PLI). Volar dislocation of the lunate then results when there is spontaneous reduction of the distal carpus, which forces the lunate in a volar direction (stage IV PLI). Displaced scaphoid fractures with greater than 1 mm of step-off indicate instability and are usually the result of incomplete or spontaneously reduced perilunate dislocation (Fig. 10.167). This is evident on MR studies with a static dorsiflexion of the lunate in a DISI deformity.

In dorsal perilunate dislocation, sagittal images demonstrate the longitudinal axis of the capitate dorsal to the longitudinal axis of the radius in association with a flexed scaphoid. In the coronal plane the carpus is foreshortened. There is an overlap of the proximal capitate and distal lunate margin with a diastasis between the scaphoid and lunate. In a lunate dislocation the longitudinal axis of the capitate is colinear with that of the distal radius and the lunate is displaced in a volar direction. There is an intermediate stage of injury that may occur in both perilunate and transscaphoid perilunate dislocations. In

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this intermediate stage of injury carpal displacements are halfway between a perilunate and lunate dislocation. The capitate is partially dorsal to the longitudinal axis of the radius and the lunate is angulated volarly but not completely dislocated. In dorsal transscaphoid perilunate dislocation there is an associated fracture of the waist of the scaphoid. In the less common volar perilunate and volar transscaphoid perilunate dislocation, the lunate is palmarly flexed and the capitate is displaced volarly (Fig. 10.168). Volar transscaphoid perilunate dislocation is usually widely displaced and is typically more unstable than its dorsal counterpart.

FIGURE 10.166 ● Scapholunate dissociation (A) associated with dorsal tilting of the lunate in a DISI deformity (B). (A) Coronal FS PD FSE image. (B) Sagittal T1-weighted image.

FIGURE 10.167 ● Unstable scaphoid fracture with greater than 1 mm of step-off at the fracture site. The scaphoid is elongated in the axial plane secondary to flexion. Scaphoid displacement indicates instability, usually from an incomplete or spontaneously reduced perilunate dislocation.

Triquetrum Fractures

Fractures of the triquetrum (Fig. 10.169) are the second most common fracture of the carpus.¹⁰⁵ Correct positioning in lateral and pronated oblique projections is usually required to identify fractures of the triquetrum in standard radiography. CT examination of the triquetrum, however, is not limited by overlapping of the proximal and distal carpal rows, which may obscure identification of a fracture line. Triquetral fractures include chip fractures that involve the dorsal surface and occur secondary to an avulsion injury at the insertional site of the ulnotriquetral ligament or to trauma to the wrist positioned in hyperextension and ulnar deviation. Fracture through the body of the triquetrum is less common. Triquetral body fractures may be associated with perilunate dislocations or ulnar carpal dissociation.

Multiple fracture lines and acute fracture through the triquetrum may obscure fracture morphology secondary to reactive hyperemia of subchondral bone. T1-weighted images in the axial, coronal, and sagittal imaging planes identify hypointense signal in the area of the fracture. In our experience, CT has been more useful in displaying cortical detail and fracture morphology.

Lunate Fractures

Fracture of the lunate is an uncommon injury that usually occurs secondary to a fall with the wrist in dorsiflexion (Fig. 10.170).¹⁰⁵ In Kienböck's disease, acute fractures of the lunate may be related to single or multiple episodes of compression, but more often they are pathologic fractures through areas of necrotic bone that occur during the advanced stages. Associated perilunate dislocation with ligamentous trauma should be evaluated.

Pisiform Fractures

The pisiform is a sesamoid bone within the flexor carpi ulnaris tendon.¹⁰⁵ Fracture of the pisiform is caused by direct or blunt trauma, such as occurs when the heel of the hand is used as a hammer. It appears as a comminuted or simple fracture. Pisotriquetral arthritis may develop secondary to pisiform fracture. Sagittal and axial

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T1-weighted images display a larger surface area of the pisiform bone, minimizing the partial volume effect that may complicate coronal images.

FIGURE 10.168 ● Volar transscaphoid perilunate dislocation associated with a scaphoid fracture, scapholunate dissociation, lunate volar flexion, and a volar shift of the capitate. This injury pattern is less common than dorsal transscaphoid perilunate dislocation. (A) Corcnal FS PD FSE image. (B) Sagittal FS PD FSE image. (c) Sagittal T1-weighted image.

FIGURE 10.169 ● Triquetral fracture of the distal pole on a coronal FS PD FSE image.

FIGURE 10.170 ● Eccentric volar ulnar-sided lunate fracture unrelated to Kienböck's disease. Volar-pole fractures of the lunate represent the most common non-Kienböck's related fracture pattern. Coronal FS PD FSE image.

Hamate Fractures

Fractures of the hamate, which account for approximately 2% of carpal fractures,¹⁰⁵ may involve either the body or the hook (i.e., the hamulus) (Fig. 10.171).¹⁰⁹ They are most frequently seen in young, active patients, especially athletes, and are somewhat more common in males than females, probably as a function of greater participation in baseball, hockey, golf, and tennis.

The hamate, which is the most ulnar bone in the distal row. supports the fourth and fifth metacarpal bases. The palmar surface has a pronounced hook, which serves as the ulnar attachment to the distal flexor retinaculum and the origins of the flexor digiti minimi and opponens digiti minimi. The pisohamate ligament connects the pisiform to the hook of the hamate distally, and the insertion of the flexor carpi ulnaris, via the pisohamate ligament, is on the palmar surface. The radial surface concavity serves as a pulley mechanism for flexor tendons and the ulnar surface articulates with the triquetrum. The distal surface articulates with the fourth and fifth metacarpals by two facets with a dividing anteroposterior ridge. The dorsal surface is triangular and roughened for ligamentous attachment. The triquetrohamate joint has a spiral orientation and influences motion between the carpal rows.

Etiology, Pathology, and Clinical Features

Hamate fractures are cortical and trabecular fractures and may involve the body of the hamate (across articular surfaces), the hook, or the proximal pole. Fractures of the body are usually nondisplaced or fracture-dislocations; hook fractures may or may not have a diastasis. The fracture line is usually transverse, although it may be oblique or comminuted in body fractures.

Fracture of the hook of the hamate may involve an avulsion injury of the transverse carpal ligament. Direct trauma to the volar aspect of the wrist, the most common mechanism of injury, usually occurs in activities that require a grasping movement, such as catching a ball or holding a bat, golf club, hockey stick, or racket. Fractures may also be caused by a fall on an outstretched wrist (dorsiflexion) and tension applied through the transverse carpal and pisohamate ligaments. The dominant hand is usually involved in

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sports-related injuries; the nondominant hand may be involved with other causes.

FIGURE 10.171 ● Fracture of the hook of the hamate on (A) a coronal illustration with sagittal inset and (B) an axial T1-weighted image. Hamate fractures may involve either the body or the hook.

Fractures of the distal hamate are usually displaced articular fractures caused by force propagated along the fifthmetacarpal shaft, as would be seen in a fall or a direct blow on a flexed and ulnarly deviated fist. Proximal pole fractures are osteochondral, and the most common mechanism of injury is impaction against the lunate articular surface (with the wrist in dorsiflexion and ulnar deviation). Osteochondral fractures of the triquetral articular surface are caused by a shearing injury or impaction against the lunate.

Body fractures and fracture-dislocations are usually caused by direct crushing injuries or punch-press accidents, such as might occur with a fall on a hyperdorsiflexed and ulnarly deviated wrist. There is often associated posterior dislocation or subluxation of the fourth or fifth metacarpals.

The articular surfaces are involved in fractures of the body of the hamate, and intra-articular fractures are seen with involvement of the capitohamate, triquetrohamate, and hamatometacarpal joints. Fractures at the base of the hook have a good blood supply and are likely to heal well. Palmar fractures of the hook, toward the tip, are subject to greater displacement and risk of nonunion. Microscopic evidence of palmar hook nonunion includes an inadequate fracture site callus, osseous resorption, and decreased cancellous vascularity.

Ring and little finger flexor tendon attritional rupture may occur with chronic fracture of the hamate. Neuropathy of the deep branch of the ulnar nerve has also been observed in these injuries.¹⁰⁵

The clinical presentation includes acute or chronic pain and tenderness of the ulnar aspect of the wrist. There may be associated ulnar nerve palsy, a decrease in grip strength, painful finger flexion, and carpal tunnel syndrome.

Imaging Evaluation and MR Appearance

Conventional radiographic imaging often yields negative results in hamate fractures, and diagnosis may require the use of a carpal tunnel projection. T1-weighted axial and sagittal images are best suited for displaying the anatomy of the hook of the hamate and for identification of hamate fractures. FS PD FSE or STIR techniques, however, are better for demonstrating associated marrow edema (Fig. 10.172). Subacute to chronic hook fractures may be missed on coronal images. Thin (1.5-mm) CT scans more accurately identify the extent and location of fractures of the hamate, especially the hook of the hamate. The proximity of the ulnar nerve to the hamate may contribute to the presentation of ulnar wrist pain in patients sustaining hamate trauma.

MR imaging findings include:

Hypoimense or hyperintense fracture line (Fig. 10.173)
A transverse fracture line of trie hook on axial images and a vertical line on sagittal images
Marrow edema of the hook or body in acute injury
Displacement of hook fractures (seen on axial or sagittal plane images)

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Displacement of articular fractures
Associated osteochondral fractures
Effacement of the ulnar aspect of the carpal tunnel at the level of the ulnar-sided flexor digitorum profundus tendons

FIGURE 10.172 ● Marrow edema is hyperintense on FS PD FSE axial (A) and coronal (B) images of a hamate hook fracture at the junction of the hook and body of the hamate.

Treatment

The majority of body fractures heal with immobilization. Fractures of the base of the hook also heal well with conservative treatment (casting or splint immobilization), but palmar fractures are at risk for nonunion. Displaced or comminuted fractures or nonunions are treated with excision. Distal articular body fractures with dislocation of fourth and fifth metacarpals require ORIF.

Capitate Fractures

Fractures of the capitate, which account for 1% to 3% of carpal bone fractures (Fig. 10.174),¹⁰⁵ are similar to scaphoid fractures in that the blood supply extends through the waist of the capitate, making the proximal pole susceptible to AVN. Capitate fractures are caused by either direct trauma or forced dorsiflexion. The most frequent site of fracture involves the waist or neck of the capitate. Sagittal MR images are helpful in assessing rotation at the fracture site. Scaphocapitate syndrome consists of a capitate fracture associated with perilunate dislocation. The mechanism of injury is dorsiflexion in radial deviation. The head of the capitate is fractured and rotated 180°,¹⁰⁵ The proximal end of the capitate demonstrates a squared-off contour.

Trapezium and Trapezoid Fractures

Fractures of the trapezium involve either its body or volar margin.¹⁰⁵ A displaced vertical fracture with lateral subluxation of the first metacarpal is treated with reduction and internal fixation. The trapezoid is the least commonly fractured bone of the carpus.

Avascular Necrosis and Nonunion of the Scaphoid

FIGURE 10.173 ● Hyperintense fluid in the hook of the hamate fracture site. Hook fractures are associated with falls, direct trauma, and striking a ball with a club (golf) or racquet (tennis). Axial FS PD FSE image.

FIGURE 10.174 ● Transverse fracture through the body of the capitate. These fractures may be isolated or occur in association with perilunate dislocation (A) Coronal T1-weighted image. (B) Coronal FS PD FSE image.

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Avascular Necrosis

AVN of the scaphoid is primarily a posttraumatic event that occurs secondary to proximal pole or waist fractures that endanger the dominant blood supply of the scaphoid (Fig. 10.175). There often is sclerosis of the proximal pole related to osteopenia and hyperemia of adjacent nonnecrotic bone. By the time sclerosis, resorption, and collapse are evident on plain film radiographs, however, the disease is in an advanced state. When AVN of the scaphoid occurs in the absence of fracture, it is called Preiser's disease (Fig. 10.176).

MR Appearance

The application of MR imaging to the detection and evaluation of AVN is facilitated by the higher-signal-intensity contrast generated from the normal fatty marrow content of the carpal bones. MR imaging has been reported to be as sensitive as bone scintigraphy in the detection of AVN, and even more specific.¹⁹^,¹¹⁰^,¹¹¹^,¹¹²^,¹¹³^,¹¹⁴ On T1-weighted (i.e., short TR/TE) sequences, MR sensitivity rates for the detection of decreased marrow signal associated with AVN are 87.5%. With the addition of T2-weighted sequences, specificity is reported to be 100%. STIR images can be used to document increased hyperemia of the distal pole marrow as well as prcximal pole vascularity, which may not be appreciated on T1-, T2-, or T2*-weighted images. Accurate assessment of vascularity may be limited on gradientecho sequences. Intravenously administered gadolinium contrast produces enhancement of hyperemic tissue at the fracture site and adjacent subchondral bone marrow.¹¹⁵ This is assessed on T1-weighted FS images. Absence of proximal pole bone marrow enhancement indicates lack of vascular perfusion in the development of AVN. CT is often used to document the extent of bridging bone spatially in a 3D rendering. A vascularized pedicle graft is a treatment option prescribed for scaphoid nonunion with a nonviable proximal fragment.

The most common MR findings in AVN of the scaphoid are:

Hypointensily in the proximal pole on both T1-weighted and FS PD FSE images (Figs. 10.177 and 10.178). In diffuse marrow necrosis, low-signal-imensity marrow may not be restricted to the proximal pole.
Localized fluid accumulation and limited marrow edema of the proximal pole
Reactive marrow hyperemia of the distal pole, which should not be confused with diffuse changes of necrosis
Fluid separating fracture fragments
Nonunion is characterized by persistent hypointensity on T1, FS PD FSE, and post-contrast FS T1-weighted images (see more detailed discussion below on nonunion of the scaphoid).
Fracture healing demonstrates hyperemia at the fracture site and adjacent marrow.
Callus or fibrous union may also demonstrate hypointensity on T1-weighted or FS PD FSE images.

Scaphoid Nonunion

Scaphoid nonunion occurs when a scaphoid fracture fails to unite within 6 months of injury (Fig. 10.179) and is indicated by the absence of bridging trabecular bone on coronal or sagittal images. It is most commonly seen in males in the second or third decade with proximal-third fractures or vertical oblique fractures of the middle third. Morphologically it appears as a prismatic defect with a quadrilateral base.

FIGURE 10.175 ● A scaphoid fracture with AVN (curved arrow) of the proximal pole is hypointense on a T1-weighted coronal image (A) and hyperintense in hyperemic viable bone on a FS PD FSE coronal image (B). The fracture line (straight arrow) remains hypointense on both pulse sequences. The FS PD FSE image is also more sensitive than the T1 -weighted image in detecting distal-pole marrow edema.

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Etiology, Pathology, and Clinical Features

Nonunion is primarily related to the severity of the injury, fracture pattern (vertical oblique fracture), fracture location (proximal third), displacement of fracture fragments (cortical offset 1 mm or more), and associated ligamentous injury and DISI. It is caused by loss of blood supply to the proximal fragment, and the smaller-diameter proximal pole is at greatest risk. The risk of development is increased by delayed diagnosis or ineffective immobilization in initial treatment.

It is characterized by stage I PLI (the triquetrum, lunate, and proximal fragment of the scaphoid slide volarly into extension) and a volar defect caused by trabecular erosion. Fragmentation and collapse of the proximal pole indicate a late stage. Histologic findings include inadequate fracture-site trabeculation, osseous resorption, and interruption of the blood supply with decreased cancellous vascularity.

Patients present with continued wrist pain, weakness of grip, and loss of dorsiflexion. Some patients are initially symptomatic after injury; others have delayed onset and do not display symptoms until degenerative changes or reinjury occurs. In displaced nonunion the symptoms are more severe than in nondisplaced nonunion. In scaphoid nonunion, osteoarthritis of the wrist begins at the radioscaphoid joint before progressing to the capitolunate articulation. SLAC occurs in the wrist with DISI and advanced degenerative change. The degenerative changes that occur in scaphoid nonunion are similar to the changes seen in scapholunate dissociation. Scaphoid nonunion is considered a greater arc injury, whereas scapholunate dissociation is a lesser arc injury, and both present as stage I PLI. Thus the tern SNAC wrist is used to represent the late degenerative changes secondary to scaphoid nonunion.

Classification

Nonunion has been classified into five types:

Type 1: Simple nonunion; it is nondisplaced and there are no degenerative changes

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Type 2: Unstable nonunion (see Fig. 10.179), with displacement (more than 1 mm) or DISI (SL angle greater 70°), but no degenerative changes
Type 3: Early arthritic nonunion with radioscaphoid arthritis
Type 4: SNAC wrist (Fig. 10.180)
Type 5: Scaphoid nonunion advanced collapse-plus (SNAC plus), and there is arthritis throughout the wrist.

FIGURE 10.176 ● Preiser's disease. A T1-weighted coronal image shows a low-signal-intensity sclerotic scaphoid (arrow) without an identifiable fracture site.

FIGURE 10.177 ● (A) Coronal illustration shows a fracture of the waist of the scaphoid with AVN of the proximal pole. The vascular supply to the proximal pole occurs via the radial artery from the distal pole. Chronic proximal-pole AVN with hypointense marrow is shown on coronal T1-weighted (B) and FS PD FSE (C) images.

FIGURE 10.178 ● AVN of the scaphoid, with early SLAC wrist (A) A low-signal-intensity “corner sign” of radial styloid subchondral sclerosis (black arrow) is seen in the presence of scaphoid nonunion and AVN of the proximal pole (large white arrow) on a T1-weighted coronal image. There is mild narrowing of the radioscaphoid articulation with respect to the distal pole (small white arrows). The scapholunate interosseous ligament is intact (open arrow). (B) Attenuated articular cartilage is seen in the proximal aspect of the distal pole of the scaphoid in early SLAC degeneration (arrows) on a T2*-weighted coronal image. The radiolunate joint is characteristically unaffected.

MR Appearance

Scaphoid nonunion is indicated by the absence of bridging trabecular bone and a prismatic defect with a quadrilateral base. Contrast administration may be necessary to define the nonunion site by enhancement of a viable proximal pole marrow. Specific findings include:

Hypointensity across the fracture site on T1- or PD-weighted images
Displacement with a cortical offset of 1 mm or more
DISI on sagittal images
Dorsal gap on sagittal images through the scaphoid
Loss of coaptation of scaphoid fracture fragments
Instability between proximal and distal carpal rows
Increased scapholunate and capitolunate angles on sagittal images
Trabecular erosion with a volar defect at the fracture site associated with scaphoid angulation
Proximal-pole AVN
Pseudoarthrosis
Degenerative loss of joint space (chondral loss) in the radioscaphoid, scaphocapitate, and capitolunate joints
SNAC
Viable marrow in the acute/subacute phase; nonviable marrow in chronic nonunion
Diffuse marrow hyperintensity on FS PD FSE images, possibly representing proximal-pole ischemia and reactive edema of the distal pole

Treatment

Almost all patients with nonunion of at least 5 years' duration progress to arthritis. The sequence of joint involvement is radioscaphoid (first), scaphocapitate (second), and then the capitolunate (third). Degenerative changes in nondisplaced nonunions are usually confined to the radioscaphoid joint, with sparing of the radiolunate joint.

For nondisplaced, acute or subacute (less than 6 months from injury) fractures, conservative treatment including immobilization and electrical stimulation may be sufficient. For symptomatic nonunion, especially in younger patients, surgery

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is necessary. The specific procedure depends on the classification of nonunion:

Type 1 simple nonunion may be treated with an inlay bone graft.
Type 2 unstable nonunion requires a volar wedge graft.
Type 3 nonunion is treated with a wedge graft, ORIF, and styloidectomy.
Type 4 (SNAC wrist) is treated with midcarpal fusion and scaphoid excision.
Type 5 (SNAC-plus) is treated with arthrodesis.

FIGURE 10.179 ● Scaphoid nonunion with persistent hyperintense fracture gap on coronal T1-weighted (A) and FS PD FSE (B) images.

Kienböck's Disease

Kienböck's disease, also known as lunatomalacia, aseptic necrosis, osteochondritis, traumatic osteoporosis, and osteitis of the lunate, is a condition marked by AVN of the lunate. The onset, which can be quite insidious, peaks between the ages of 20 and 40 years. There is a 2:1 male-to-female ratio. Although uncommon, bilateral disease does occur. In approximately 80% of cases the lunate is supplied by both palmar and dorsal nutrient vessels. In 20%, however, a single palmar vessel provides the sole blood supply for the lunate. There are three patterns of intraosseous blood supply to the lunate:

Y pattern, present in approximately 60% of individuals
I pattern, present in approximately 30%
X pattern, present in approximately 10%

The differential diagnosis includes dorsal ganglion cysts, rheumatoid arthritis, degenerative or posttraumatic arthritis, synovitis of the wrist from any cause, acute fractures, carpal instabilities, and ulnar impingement syndrome. It is critical that Kienböck's disease be suspected when evaluating dorsally located central wrist pain. In stage I Kienböck's disease, plain film radiograph findings are normal. Before MR imaging became available, the standard test at this stage was the three-phase ⁹⁹mTC-MDP study. ¹⁶ When there is abnormal uptake of technetium, especially in the third or delayed phase, a CT scan should be performed to assess trabecular bone morphology and to identify fractures. The three-phase technetium study is extremely sensitive but does not provide detail about physiologic changes in the marrow, which can be seen on MR scans. MR imaging is potentially the best first imaging examination after routine radiographs (Fig. 10.181). MR imaging not only allows assessment of the lunate, but also facilitates ruling out or adding other disorders in the differential diagnosis. MR studies may reveal occult ganglion cysts as well as inflammatory arthritides with synovitis.

Etiology, Pathology, and Clinical Features

In 1928, Hulten noted a correlation between negative ulnar variance and the occurrence of Kienböck's disease.¹¹⁷ He found that 78% of patients with Kienböck's disease had a relatively short ulna, whereas only 23% of patients with normal wrists had negative ulnar variance.¹¹⁷ Despite his primitive radiographic

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techniques and measurement methods, this correlation has withstood the test of time. The association between a short ulna and Kienböck's disease is not absolute. Although exceedingly uncommon, Kienböck's disease may also occur in patients with neutral or positive ulnar variance. The significance of negative ulnar variance is that it subjects the lunate to an increased mechanical load compared with that associated with neutral or positive ulnar variance.

FIGURE 10.180 ● Scaphoid nonunion advanced collapse (SNAC), with components of both a scaphoid nonunion and SLAC arthntis. SNAC is considered a greater arc injury. (A) Coronal T1-weighted image. (B) Coronal FS PD FSE image. (C, D) In a separate case. SNAC wrist demonstrates features of early SLAC arthritis (stage I) with distal-pole scaphoid-radial styloid arthrosis, fracture nonunion, and AVN of the scaphoid proximal pole. The smaller proximal-pole scaphoid fragment adjacent to the scapholunate interval is a secondary sign of scaphoid instability. (C) Coronal T1- weighted image. (D) Coronal FS PD FSE image.

FIGURE 10.181 ● Kienböck's disease. (A) An AP radiograph displays sclerosis and collapse of the lunate (arrows) associated with negative ulnar variance. (B) The corresponding T1 -weighted coronal image shows a low-signal-intensity necrotk lunate (open arrow), a disrupted scapholunate ligament (large solid arrow), and an intact TFC (small solid arrows).

In measuring ulnar variance, it is important to remember that the relative lengths of the ulna and radius vary with the position of the forearm, and it is critical that measurements be made with the forearm in neutral pronosupination. There is no evidence that Hulten was aware of this, and he did not control the forearm position in his studies. When forearm position is carefully controlled, there is virtually no difference in accuracy among the several methods available for measuring variance. Gelberman et al.¹¹⁸ have developed a simple method that requires no special tools. In this technique, a line is extended perpendicularly from the most proximal portion of the distal radial articular surface. This point can be found by carefully inspecting PA radiographs for the three sclerotic lines that represent different portions of the articular surface. The most distal line is the dorsal lip of the radius. The middle line, because of the normal volar tilt of the distal radius articular surface, is the volar lip of the radius. The most proximal line is the most proximal portion of the articular surface, and this is where the perpendicular line should originate. The distance between this line and the distal articular surface of the ulna is then measured.

In addition to negative ulnar variance (ulnar minus), other risk factors for Kienböck's disease include susceptible lunate geometry (oblong or square), vulnerable lunate vascularity, and TFC complex compliance (the TFC complex is thicker in negative ulnar variance). The mechanism of injury may be acute trauma, or repeated minor trauma secondary to excessive shear force, which causes interruption of the blood supply to the lunate, which is anatomically susceptible because of a single nutrient vessel or compromised intraosseous blood supply. The theory that acute fractures and trauma play a role in the etiology of Kienböck's disease, an essentially progressive disease, dates as far back as 1843.¹¹⁹ It is the anatomy of the vascular supply of the lunate that places it at risk for the development of AVN. Gelberman et al. found that all lunates could be classified into three types based on their intraosseous microvascular anatomy (Fig. 10.182).¹²⁰ The extraosseous blood supply was found to be abundant, and AVN could not be ascribed to interruption of these vessels at a single pole of the lunate. However, the subchondral bone adjacent to the radial articular surface was found to be relatively avascular, and this is the area where collapse is most commonly seen. Gelberman et al. concluded that AVN is secondary to disruption of the intraosseous blood vessels caused by repeated trauma and compression fractures.

Pathologic findings include evidence of a fracture, cystic changes, fragmentation and collapse, and radiocarpal or midcarpal arthritis. Hislologically there is evidence of venous stasis, necrosis of bone, and an inflammatory response.

Initially, patients note dorsal tenderness about the lunate and may develop stiffness due to synovitis. The synovitis and inflammation may affect surrounding structures, and acute carpal tunnel syndrome may be the presenting complaint. Patients also report weakness, limited motion, diffuse swelling, and decreased grip strength. The disease is usually

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unilateral, although there are incidences of bilateral disease. Kienböck's disease is a great dissembler, and a number of other conditions should be considered. Any history of trauma should be carefully elicited.

FIGURE 10.182 ● Three patterns of the interosseous vascular supply of the lunate. Acute trauma or repeated microtrauma with excessive shear force results in interruption of the blood supply to a lunate susceptible to or at risk for Kienböck's disease. A single nutrient vessel or compromised intraosseous blood supply places the lunate at risk. Sagittal color illustrations.

Staging and Classification

The clinical and imaging characteristics of Kienböck's disease vary according to the stage of the disease.¹²¹ There are several classification systems, including:

Stahl's classification, based on clinical and radiographic criteria
Decoulx's modification of Stahl's system, in which the presence of a fracture is not required in early stages
Lichtman's staging classification, which involves three stages described in detail below
An MR classification based on Lichtman stage II (discussed later under MR appearance)

Lichtman's staging classification, which has the most clinical relevance (Fig. 10.183), divides the disease into three primary stages, with two subclassifications in stage III.¹²²

Stage I

Plain radiographs are normal, with the possible exception of a linear or compression fracture in the lunate. Ulnar variance should be noted.

Stage II

There is a change in the density of the lunate, which, although it has not undergone any changes in its architecture, appears to be quite sclerotic compared with the other bones of the carpus. There is no significant carpal instability, but there may be a slight degree of collapse of the radial side of the lunate.

Stage III

There is collapse of the entire lunate. Stage III is further subdivided into stages IIIA and IIIB. In stage IIIA, there is lunate collapse but scaphoid rotation is not fixed. There may be dynamic rotatory subluxation, but this can be treated with surgical reconstruction. In stage IIIB, there is lunate collapse with fixed scaphoid rotation and proximal migration of the capitate (i.e., dissociative carpal instability). There is also a decrease in the carpal height ratio.

Stage IV

Stage IV has all the findings of stage III, with the addition of generalized arthritic changes throughout the carpus.

MR Appearance

In general, the most obvious diagnostic sign of Kienböck's disease on an MR examination is a hypointense lunate on T1- or PD-weighted images. There may be centralized or diffuse, but not eccentric, sclerosis and a linear (transverse) or compression fracture. Contrast administration and FS techniques allow differentiation of enhancing viable marrow.

Specific MR findings in Kienböck's disease can also be grouped according to the stage of disease.¹¹⁴

Stage I

As mentioned earlier, conventional radiographs are usually normal in stage I, although an associated fracture line or compression fracture may be present. At this early stage, bone scintigraphy is both sensitive and nonspecific for the diagnosis of Kienböck's disease. However, bone scintigraphy is poor in differentiating fractures, osteochondral lesions, erosions, and the spectrum of degenerative changes that present as subchondral sclerosis. MR imaging offers comparable or greater sensitivity and improved specificity when compared with scintigraphy or radiographs (Fig. 10.184). With MR imaging, it is possible to characterize the extent of necrosis and the morphology of marrow involvement, as well as the overall morphology of the lunate cortical surfaces, including articular cartilage. Focal or diffuse low signal intensity is seen on T1-weighted images in affected areas of marrow involvement. Coronal plane images best display the largest anterior-to-posterior surface area of involvement. The addition of sagittal or axial images provides more accurate assessment of the volume of marrow involvement. On T2*-weighted images, the lunate demonstrates uniform low signal intensity. Normal lunate marrow or recovering marrow vascularity usually displays a central region of mildly increased signal intensity or inhomogeneity on gradient-e-cho images. STIR sequences are more sensitive to hyperemia or vascular dilation and demonstrate increased signal intensity restricted to the lunate.

In early Kienböck's disease, T1-weighted images show unaffected marrow with the high signal intensity of fat, isointense with the other carpal bones of the wrist. The distribution of low-signal-intensity necrosis may be restricted to a portion of the volar or dorsal coronal plane or may demonstrate an eccentric or central region of involvement. Radiocarpal joint effusions, or more localized synovitis, demonstrate increased signal intensity on T2-weighted (FS PD FSE), T2*-weighted, and STIR sequences.

FIGURE 10.183 ● The four stages of Kienböck's disease. In contrast to stages I and II, stages III and IV are characterized by lunate collapse in the coronal plane and elongation of the lunate in the sagittal plane. Associated findings (in stage III and IV) include proximal migration of the capitate, scapholunate dissociation, scaphoid flexion, and ulnar migration of the triquetrum. Stage IV has generalized degenerative changes of the carpus. Extensive lunate marrow edema is associated with stage I Kienböck's disease. (A) Sagittal color illustration. (B) Sagittal FS PD FSE image. (C) Coronal T1-weighted image.

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Interval MR imaging can be used to show the progression of Kienböck's disease or to document healing with the return of normal marrow signal intensity in stage I disease (Fig. 10.185). The relative osteopenia of the remaining carpus is not seen using MR techniques. Intravenous gadolinium with FS displays hyperemic bone with increased signal intensity.

Stage II

MR findings in Lichtman stage II Kienböck's disease can be generally grouped into the following subclasses:

Stage IIA: A focal area of central hypointnsity on T1- weighted images that increases on T2-weighted images
Stage IIB: A focal area of central hypointnsity on both T1- and T2-weighted sequences
Stage IIC: Generalized hypointensity on T1-weighted images that increases on T2- weighted images
Stage IID; Generalized hypointensity on T1- and T2-weighted images

Plain film radiographs in stage II show sclerosis of the lunate that corresponds to low-signal-intensity areas on T1-weighted MR images, areas of viable marrow hyperintensity on STIR images (Fig. 10.186), and low or low to intermediate signal intensity on T2-weighted images. Edema, granulation tissue, and areas of preserved vascularity demonstrate increased or high signal intensity on T2-weighted images. Generally, although morphology and size are preserved, there is decreased height of the radial aspect of the lunate in late stage II disease.

Stage III

In stage III the lunate undergoes distal-to-proximal collapse in the coronal plane and elongation in the sagittal plane (Fig. 10.187). There is reciprocal proximal migration of

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the capitate. The absence or presence of scapholunate dissociation with rotatory subluxation of the scaphoid divides patients into stage IIIA and IIIB, respectively. Rotation of the scaphoid may be accompanied by ulnar deviation of the triquetrum. With scaphoid rotation, the inability to see the entire long axis of the scaphoid in a single coronal image is the MR equivalent of the radiographic “ring” sign on conventional AP radiographic projections. Articular cartilage degeneration can be identified in this stage.¹²³

FIGURE 10.184 ● Stage I Kienböck's disease without visible fracture line. (A) Color coronal illustration. (B) Coronal T1-weighted image. (C) Coronal FS PD FSE image.

Stage IV

Stage IV is characterized by degenerative arthrosis of the lunate and carpus (Fig. 10.188). There are no regions of increased signal intensity on T2*-weighted or STIR images in this advanced stage of the disease, and lunate collapse can be defined in all three orthogonal planes. Splaying of the volar and dorsal poles of the lunate is accompanied by extrinsic effacement and convex bowing of the flexor tendons in the sagittal plane. This may contribute to symptoms of carpal tunnel syndrome, especially if there is associated proximal migration of the flexor retinaculum with wrist shortening. Fragmented portions of the lunate usually demonstrate low signal intensity on T1- and T2*-weighted images. Thin-section (1.5-mm) CT scans provide more accurate assessment of cortical fragmentation.

Kienböck's disease may also be associated with Madelung's deformity, a developmental anomaly involving the distal radius and carpus. Synovitis is seen in the advanced stages, characterized by a high-signal-intensity radiocarpal effusion that often

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distends synovial recesses. Pannus tissue is low to intermediate in signal intensity on T1- weighted and FS PD FSE images and enhances with gadolinium intravenous contrast.

FIGURE 10.185 ● (A) Recovering fatty marrow signal intensity (large arrow) is present after treatment of stage I Kienböck's disease of the right wrist. The lunate and TFC (small arrows) are normal. A low-signal-intensity postoperative artifact secondary to radial shortening is present (open arrows). (B) The untreated left wrist shows severe negative ulnar variance (black double-headed arrow) and a deformed but intact TFC (white arrows). The lunate marrow is unaffected.

In review, key MR findings include:

Stage I
- A hypointense to hyperintense transverse fracture line (Fig. 10.189)
- Microtrabecular compression fractures, more common than well-defined transverse fracture
- Marrow hyperintensity on FS PD FSE images (see Fig. 10.184)
- Intermediate-signal-intensity synovitis on FS PD FSE images
Stage II
- Centralized to diffuse marrow hypointensity on T1- and PD-weighted images (see Fig. 10.181)
- Intact shape of lunate
- Subtle collapse (stage II) of lunate on radial border on coronal images
- Hypointense to hyperintense fracture lines, if present
- Viable marrow hyperintense on FS PD FSE or STIR images
- Decreased height of the radial aspect of the lunate on coronal and sagittal images
Stage III
- Lunate collapse plus proximal migration of capitate
- Anteroposterior elongation of lunate in sagittal plane
- Proximal migration of capitate on coronal images
- Associated scapholunate dissociation with hyperintensity of the scapholunate ligament on FS PD FSE images
Stage IV
- Sclerosis plus osteophyte formation and areas of reactive marrow degeneration
- Loss of articular cartilage in radiocarpal and midcarpal articulations

Treatment

The treatment of Kienböck's disease is a subject of debate among hand surgeons. No single surgeon or center has been able to develop a large enough experience with all stages of the disease to provide truly definitive treatment recommendations. As a result, many types of procedures are recommended in the literature.

In general, treatment modalities are tailored to the stage of disease. Early stages, which are marked by the absence of changes in articular cartilage, minimal collapse of the lunate, and permanent carpal instability patterns, are usually treated with procedures designed to unload and revascularize the lunate, including radial wedge osteotomy and scaphoid-trapezium-trapezoid or scaphocapitate fusion. Later stages, with established instability patterns and degenerative arthritis, are treated with arthrodesis and salvage procedures such as proximal row carpectomy. Therapeutic strategies correlate with the transition from stage IIIA to stage IIIB disease.

FIGURE 10.186 ● Stage II Kienböck's disease with (A) increased lunate density (sclerosis) on coronal reformatted CT scan and (B) corresponding marrow hyperintensity on fast STIR coronal image. (C) A separate case of stage II Kienböck's disease with visible proximal subchondral fracture line

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Stage I

The initial treatment after diagnosis is immobilization and nonsteroidal anti-inflammatory drugs. Immobiliza-tion will help to differentiate transient ischemia from Kienboöck's disease. If there is no improvement with this treatment, then surgical intervention should be considered. A halfway step to an open surgical procedure is the placement of an extended fixation device with distraction to unload the lunate. Although this may help, it is impossible to keep such an appliance in place for more than 3 months, which is insufficient time to allow revascularization. If the patient has negative ulnar variance, then radial shortening is frequently advocated to unload the lunate. Although ulnar lengthening is equally effective, it is technically more demanding. Surgical intervention in stage I is rarely indicated, and all patients should receive a trial of conservative therapy. MR imaging is useful for both early detection and to document healing during cast immobilization.

Stage II

At this stage, conservative therapy is not effective, and unloading, revascularization, or both procedures are necessary. This is probably the optimal time for performing a revascularization procedure. Prior to surgery, CT scans should always be performed to assess bone detail, in order to identify any repairable fractures.

FIGURE 10.187 ● Stage III Kienböck's with lunate collapse identified in both coronal and sagittal planes. (A) Coronal T1-weighted image. (B) Sagittal FS PD FSE image.

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There are two approaches to revascularization. One entails transferring a vascularized bone graft to the lunate, and Braun has successfully used a portion of radial bone for this transfer.¹²⁴ Revascularization with transplantation of a vascular pedicle into the lunate was first reported in 1979 and has gained in popularity.¹²⁵ In this procedure, the second intermetacarpal artery with its vena comitantes is passed through a dorsal-to-volar hole in the lunate. Studies verify that as long as the vena comitantes is present, the artery remains patent. Unloading procedures can also be combined with revascularization. Radial shortening and ulnar lengthening are options in the wrist with negative ulnar variance. In the patient with neutral or positive ulnar variance, Almquist et al.¹²⁶ introduced the technique of shortening the capitate by osteotomy to unload the lunate. They have shown that shortening the capitate by 2 to 4 mm reduces the load on the lunate significantly and produces a good clinical result.

Intercarpal fusions have also been shown to unload the lunate. Triscaphe (i.e., scaphoid-trapezoid-trapezium) and scaphocapitate fusions both appear to be effective.

Stage III

Unloading procedures may still be effective in stage IIIA. If a triscaphe or scaphocapitate fusion is done, the scaphoid fragments can be excised and the space left empty. Formerly, stage IIIA disease was treated by lunate excision and replacement with a silicone prosthesis, but reviews have shown a poor functional result and the frequent occurrence of silicone synovitis.¹²⁷ This procedure and use of the prosthesis are no longer indicated. In patients with positive ulnar variance, capitate

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shortening, with or without revascularization with a vascular pedicle, can be used to unload and revascularize the lunate. Radial shortening is substituted for capitate shortening in the patient with negative ulnar variance. During revascularization. every attempt should be made to reconstruct the lunate. When the dorsal cortex is entered, the collapsed articular surface can be elevated and buttressed with a bone graft. The vascular pedicle is then inserted.

FIGURE 10.188 ● Stage IV Kienböck's disease with lunate collapse and associated degenerative changes. (A) Coronal T1-weighted image. (B) Coronal T2*-weighted image.

FIGURE 10.189 ● Discrete transverse fracture line associated with stage I Kienböck's disease. (A) Coronal color illustration. (B) Coronal T1-weighted image. (C) Coronal T2* gradient-echo image.

In stage IIIB, the fixed rotation of the scaphoid must be corrected. Careful assessment of the scaphoid fossa is important in these patients, and MR imaging can be used for preoperative identification of thinning of the cartilage and arthritic changes in the radial styloid. With fixed rotation of the scaphoid, there is noncongruous loading of the scaphoid fossa. This situation is identical to that in SLAC wrist.

If the cartilage is intact, the procedure of choice fixes the scaphoid in a normal anatomic position with congruous loading of the scaphoid fossa and simultaneously unloads the lunate. A scaphotrapeziotrapezoid or scaphocapitate fusion, with careful attention to reducing the scaphoid, can accomplish this. In most cases, the collapsed lunate should be excised.

Stage IV

At this point, the disease process is advanced and some type of salvage procedure is necessary. If the articular cartilage in the lunate fossa of the distal radius and the proximal pole of the capitate is in acceptable condition, then a proximal-row

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carpectomy can be performed. Because of the tenuous vascular supply of the lunate, there is usually degeneration in the lunate fossa, although occasionally the distal articular surface of the lunate remains serviceable. In these cases, a radioscapholunate fusion may preserve motion at the intercarpal joint. This is not common, however, and arthritic degeneration is usually so advanced throughout the carpus that there is no choice but to perform a panarthrodesis of the wrist. Although there is a total loss of wrist motion, the patient is usually quite happy because of the pain relief.

Carpal Tunnel Syndrome

Carpal tunnel syndrome is a clinical symptom complex secondary to compression of the median nerve at the carpal tunnel. It is most often found in patients between 30 and 60 years of age and has a female-to-male ratio of between 3 to 5:1: up to 50% of cases are bilateral.¹²⁸ The disorder has a 50% lifetime incidence, but that increases up to 100% with repetitive motion activity. Carpal tunnel syndrome is also discussed in Chapter 12.

Related Anatomy

Knowledge of the anatomy of the carpal tunnel is important in understanding the pathophysiology of this syndrome. The following structures and concepts are relevant:

The carpus has a concave bony contour on its flexor surface and is covered by the flexor retinaculum (Fig. 10.190).
The bony carpus forms the floor and walls of the carpal tunnel, with the rigid flexor retinaculum as its roof (Fig. 10.191).
The flexor retinaculum, or transverse carpal ligament, attaches to the tubercle of the scaphoid, the ridge of the trapezium, and the ulnar aspect of the hook of the hamate and pisiform.
The long flexors of the fingers and thumb pass through the carpal tunnel (Fig. 10.192). The separate flexor digitorum superficialis tendons are arranged in two rows, with the tendons to the middle and ring finger volar to the tendons to the index and little finger. The flexor digitorum profundus tendons are arranged in the same coronal plane, and the tendon to the index finger is separated from the adjacent three profundus tendons. All eight flexor tendons are invested in a common synovial sheath. The flexor pollicis longus tendon, invested in its own synovial sheath, is located on the radial aspect of the flexor tendons within the carpal tunnel.
The median nerve is deep to the flexor retinaculum and is seen on the lateral side of the flexor digitorum superficialis between the flexor tendon of the middle finger and the flexor carpi radialis.

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The proximal fibers of the volar carpal ligament contribute to the roof of the carpal tunnel, although this contribution is not as significant as that of the thicker flexor retinaculum.
In dorsiflexion and palmarflexion of the wrist, the median nerve is forced against the transverse carpal ligament. This is compounded by friction forces between the median nerve tendons and the transverse carpal ligament during flexion and extension, with up to 20 mm of excursion of the median nerve.

FIGURE 10.190 ● The flexor retinaculum (transverse carpal ligament) completes the boundary of the carpal tunnel on the palmar side.

FIGURE 10.191 ● Flexor retinaculum at the level of the pisiform. The flexor retinaculum holds the flexor tendons in place during wrist flexion to prevent bowstringing and loss of power. FDP, flexor digitorum profundus; FDS, flexor digitorum superficialis; FCR, flexor carpi radialis. Axial T1-weighted image.

FIGURE 10.192 ● The relationship of the flexor tendons, median nerve, and flexor retinaculum shown on a coronal color illustration. The flexor retinaculum is under constant tension and helps maintain the contour of the carpal arch. FDP, flexor digitorum profundus; FCR, flexor carpi radialis; FPL, flexor pollicis longus.

The median nerve is round or oval at the level of the distal radius and becomes elliptical at the pisiform and hamate (Fig. 10.193). The position and morphology of the median nerve are altered during flexion and extension. With the wrist in a neutral position, the median nerve is seen anterior to the flexor digitorum superficialis tendon of the index finger or posterolaterally between the flexor digitorum tendon of the index finger and flexor pollicis longus tendon. In wrist extension, the median nerve assumes a more anterior position, deep to the flexor retinaculum and superficial to the

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flexor digitorum superficialis tendon of the index finger. In wrist flexion, the median nerve can be found anterior to the flexor retinaculum or between the flexor digitorum superficialis tendons of the index finger and thumb or middle and ring fingers. In the flexed position, there is flattening of the elliptical shape of the median nerve. Alteration of morphology is less significant in wrist extension. The morphology of the median nerve may also change with involvement by benign peripheral nerve sheath tumors. These lesions may present extrinsic to the median nerve (schwannoma) or may not be separate from the median nerve fascicles (neurofibroma) (Fig. 10.194).

FIGURE 10.193 ● (A) Anatomy of a peripheral nerve demonstrating myelinated and unmyelinated axons. The perineurium binds the separate nerve fascicles together. Axial color cross-section. (B) Variation in the position of the motor fascicle within the cross-section of the median nerve. Axial color cross-section. (C) Normal fascicles of the median nerve on an axial FS PD FSE image. (D) Hyperintense fascicles of the median nerve on an axial FS PD FSE image.

Etiology, Pathology, and Clinical Features

The impairment of motor and/or sensory function of the median nerve as it transgresses the carpal tunnel (i.e., carpal tunnel syndrome) is most often idiopathic¹²⁹ and associated with aging (Fig. 10.195). Other conditions that affect either the median nerve itself or the carpal tunnel may also be factors. In carpal tunnel syndrome, wick catheter measurements show increased pressures in the carpal canal (i.e., 32 mm Hg compared with 2.5 mm Hg in asymptomatic patients).¹²⁸ Pressure changes may also be recorded in extremes of dorsiflexion and palmarflexion. CT studies of patients with carpal tunnel syndrome show a decreased cross-sectional area of the carpal canal. Some of the processes that can cause decreased volume or space within the carpal canal include tenosynovitis of the flexor tendons, Colles' fracture, fracture-dislocation of the carpus and carpometacarpal joints, inflammation, and granulomatous infectious processes. These disorders may also cause posttraumatic scarring, fibrosis, or both, within the carpal tunnel and a proliferative tenosynovitis with hyperplastic synovium. Tumors also produce space-occupying encroachment of the carpal canal.¹²⁸^,¹³⁰ Systemic disorders that produce a volume increase within the carpal tunnel include acromegaly. hypothyroidism, pregnancy, diabetes mellitus, and lupus erythematosus. Volumetric increases are also seen in post-menopausal women. These systemic processes may increase extracapsular fluid retention and produce soft-tissue swelling. Developmental etiologies responsible for carpal tunnel syndrome include a persistent median artery, hypertrophied lumbricals, anomalous muscles, and a distal position of the flexor digitorum superficialis muscle.

FIGURE 10.194 ● Neurofibroma (small straight arrow) of the motor branch of the median nerve (m) demonstrates intermediate signal intensity on T1-weighted axial image (A) and hyperintensity on (curved arrow) (corresponding to the affected motor branch of the median nerve) demonstrates increased signal intensity on T1-weighted and STIR axial images. (B). Thenar muscle denervation (curved arrow) (corresponding to the affected motor branch of the median nerve) demonstrates increased signal intensity on T1-weighted and STIR axial images. Surgical photograph (C) shows the tumor (arrow) in situ. D, distal; P, proximal.

FIGURE 10.195 ● Carpal tunnel syndrome with hyperintense median nerve at the level of the distal carpal row. (A) Coronal FS PD FSE image. (B) Axial FS PD FSE image.

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Conditions commonly associated with the development of carpal tunnel syndrome include:

Fractures and dislocation about the wrist (e.g., Colles' fracture), which result in decreased volume of the carpal tunnel or direct nerve trauma
Inflammatory processes (Fig. 10.196), such as rheumatoid arthritis, gout and pseudogout, and amyloidosis
Median nerve tumors¹³¹ including neurilemmomas (schwannomas) (Fig. 10.197), fibromas, and hamartomas (Fig. 10.198)
Tumors (space-occupying), including ganglions (Fig. 10.199), lipomas (Fig. 10.200), and hemangiomas
Intraneural hemorrhage
Infection
Infiltrative disease
Soft-tissue injuries
Anomalous muscles,¹³² which act as a space-occupying mass (Fig. 10.201)

The carpal tunnel syndrome can thus be produced by compression or swelling of the median nerve in its synovial sheath. In the differential diagnosis of carpal tunnel syndrome, it is important to exclude median nerve damage at a more proximal level. In the case of median nerve damage, the palmocutaneous branch of the median nerve may be affected, causing weakness of the corresponding flexor muscles of the forearm, including the flexor pollicis longus tendon. This is in contrast to carpal tunnel syndrome, in which the terminal phalanx of the thumb demonstrates normal flexion without motor impairment. Although the median nerve is composed of both sensory and motor nerve fibers, the sensory fibers predominate at the level of the carpal tunnel, explaining the initial findings of sensory deficit with numbness or paresthesias of the thumb, index finger, and middle half of the ring finger. As the disease progresses, there is wasting and weakness of the thenar muscles, with decreased opposition of the thumb and anesthesia of the three-and-a-half digits on the thumb (radial side) of the hand. There is no anesthesia of the thenar eminence, which is supplied by the cutaneous branch of the median nerve.

On pathologic examination inflammation is found in approximately 10% of cases, edema in 85%, and vascular sclerosis in 98%. Tenosynovitis is relatively uncommon but connective tissue degeneration is common. Histologically there is evidence of increased pressure, impairment of intraneural microcirculation, and ischemia (the severity of which correlates with symptoms). The thin afferent nerve fibers are most susceptible to pressure. A fibrosynovial noninflammatory synovium may also occur in response to chronic frictional and/or mechanical stresses.

The clinical presentation includes:

Pain and numbness or tingling in the median nerve distribution with increased nocturnal pain and/or burning (can be classified as mild, moderate, or severe based on electrodiagnostic data or by severity of clinical symptoms)

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Involvement of the thumb, index, middle fingers, and radial half of the ring finger is most common.
Sensory findings ranging from minimal hypesthesia to complete anesthesia
Muscle atrophy and loss of function are usually late findings, although abductor pollicis brevis involvement and opponens weakness may be seen earlier (opponens atrophy is a late finding).
Positive clinical tests for nerve entrapment:
Tinel's sign (i.e., paresthesias reproduced by tapping over the median nerve), indicating nerve entrapment
Phalen's test (i.e., symptoms produced after 30 seconds with the wrist in forced palmarflexion)
Carpal tunnel compression tests (i.e., symptoms produced by manual compression with the wrist in flexion, most accurate)
Prolonged sensory conduction or distal motor latency tests (electrodiagnostic tests in patients with carpal tunnel syndrome are reported to be 85% to 90% accurate, with a false-negative rate of 10% to 15%)
Semmes-Weinstein monofilament test with the wrist in both neutral and flexed positions

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Kimura inching technique
Ring finger differential measurements

FIGURE 10.196 ● Tenosynovitis (fibrosynovial) with symptoms of carpal tunnel syndrome. (A) Coronal color illustration. (B) Axial FS PD FSE image. (C) Axial FS PD FSE in a separate case of pigmented villonodular synovitis. Connective tissue degeneration, edema, and vascular sclerosis occur with a fibrosynovial noninflammatory synovium. True tenosynovitis is less common.

FIGURE 10.197 ● Benign peripheral nerve sheath tumor of the median nerve proximal to the carpal tunnel on an axial FS PD FSE image.

MR Appearance

The ability to display the cross-sectional anatomy of the median nerve and adjacent structures on axial MR images and to trace the flexor tendons on coronal plane images makes MR imaging valuable in characterizing normal anatomy and pathology in the carpal tunnel.¹³³^,¹³⁴^,¹³⁵^,¹³⁶^,¹³⁷ Early detection of the cause of carpal tunnel syndrome requires soft-tissue discrimination not possible with standard radiographs or CT. Axial and coronal MR images of the wrist are useful for evaluating patients with a clinical presentation of median nerve deficits.

Regardless of the etiology of carpal tunnel syndrome, the changes in the median nerve are similar and include:¹³⁴

Cross-sectional enlargement and hyperintensity of the median nerve on FS PD FSE or STIR images, located deep to the flexor retinaculum
Swelling or segmental enlargement of the median nerve, best evaluated at the level of the pisiform
Flattening of the median nerve, best demonstrated at the level of the hamate
Palmar bowing of the flexor retinaculum, assessed at the level of the hamate.¹³⁶

Comparison with the contralateral wrist may be misleading, because involvement is bilateral in half to two thirds of patients with carpal tunnel syndrome.

FIGURE 10.198 ● Fibrolipoma of the median nerve with mixed fat, fibrous, and nerve fascicle signal intensity. Distal thenar muscle denervation is shown. (A) Axial T1-weighted image. (B) Axial FS PD FSE image.

FIGURE 10.199 ● Volar ganglion extending from the triscaphe articulation deforms the deep carpal tunnel and results in median nerve compromise. (A) Axial FS PD FSE image. (B) Coronal FS PD FSE image.

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Alterations in the median nerve signal intensity are nonspecific and may represent edema or demyelination within neural fibers. Signal intensity may be decreased when there is fibrosis of the median nerve. Compression and flattening of the median nerve at the level of the hamate may be demonstrated, along with bowing of the flexor retinaculum. Ratios of swelling can be calculated by dividing the cross-sectional area of the median nerve at the level of the pisiform and the hamate by the cross-sectional area of the median nerve at the level of the distal radius.¹³⁴^,¹³⁵ Significant differences, with doubling of ratios of swelling, have been shown in patients with carpal tunnel syndrome, despite the subjective flattening of the median nerve at the lateral and distal carpus. Ratios of flattening have been used to document statistically significant flattening of the median nerve at the level of the hamate.¹³⁵^,¹³⁶ The median nerve may display enlargement or dilation at the level of the pisiform, and compression with flattening at the level of the hook of the hamate.

FIGURE 10.200 ● Lipoma as a space-occupying lesion deep to the carpal tunnel on a T1-weighted axial image.

Increased signal intensity of the median nerve, best demonstrated on axial gradient-echo, FS PD FSE, or STIR images, may be accompanied by an increase in its cross-sectional diameter. Degenerative arthritis and instabilities in advanced arthrosis may cause a decrease in the cross-sectional area of the carpal tunnel and produce symptoms of carpal tunnel disease. MR imaging is most useful in characterizing space-occupying lesions, whether they be tenosynovitis, ganglions, lipomas, or granulomatous infections.

Enlargement or swelling of the median nerve proximal to the carpal tunnel, referred to as a pseudoneuroma, has also been documented with MR imaging. This condition may actually

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be associated with constriction of the median nerve within the carpal tunnel, distal to the point of swelling.

FIGURE 10.201 ● Accessory flexor digitorum superficialis muscle resulting in median nerve compression on (A) coronal color illustration and (B) axial T1-weighted MR image.

FS PD FSE or STIR images are more sensitive to nerve edema than non-FS images. Contrast-enhanced images are useful for demonstration of fibrosis of the median nerve. Dynamic contrast-enhanced MR imaging can be used to document circulatory disturbance as a cause of carpal tunnel syndrome, separate from deformation or compression of the median nerve.¹³⁸ Two abnormal patterns of median nerve enhancement are shown: there is either marked enhancement attributed to nerve edema or lack of enhancement attributed to nerve ischemia. Wrist flexion or extension may alter the pattern from marked enhancement to a lack of enhancement associated with exacerbation of clinical symptoms.

After transverse carpal ligament release, chronic induration is seen as an area of neural constriction on MR images. Residual hyperintensity of the median nerve within the carpal tunnel may be identified when there is incomplete release of the flexor retinaculum. Release of the transverse carpal ligament from the hook of the hamate may cause the flexor tendons or contents of the carpal canal to demonstrate a volar convexity because of the loss of the normal roof support of the flexor retinaculum. Widening of the fat stripe posterior to the flexor digitorum profundus tendons is a normal postoperative finding. In addition to incomplete release of the flexor retinaculum, MR changes in failed postoperative carpal tunnel surgery include excessive fat within the carpal tunnel, neuromas, and persistent neuritis.

In review, MR imaging features of carpal tunnel syndrome include:

Swelling or segmental enlargement of the median nerve at the level of the pisiform, intermediate on T1- or PD-weighted images and hyperintense on FS PD FSE images (Fig. 10.202)
Flattening of the median nerve at the level of the hamate
Palmar bowing of the flexor retinaculum at the level of the hamate
Displaced proximal half of a capitate fracture
Impingement in perilunar dislocation
Fracture of the radius (Colles' or Smith's)
Pseudoneuroma (swelling of the median nerve proximal to the carpal tunnel)
Ganglions (of triscaphe origin) that project deep to the carpal tunnel and compress the canal (see Fig. 10.199)
Thickening of the tenosynovium of the flexor tendons
Thenar muscle denervation (Figs. 10.203 and 10.204)
Incomplete release of the flexor retinaculum is associated with residual nerve hyperintensity on FS PD FSE images.

Treatment

Without treatment there is progression of pain with paresthesias and intermittent to constant numbness. Weakness of the thumb results from chronic compression. Initial treatment is conservative and includes maintenance of the wrist in a neutral position with splints, avoidance of activities that cause prolonged palmar flexion or extension, nonsteroidal anti-inflammatory agents, corticosteroid injections, or a combination of these.¹²⁸ Patients who receive the greatest short-term relief with corticosteroid injections have better results with surgical decompression.

Surgical decompression is recommended when there is progressive sensory loss, muscle atrophy plus weakness, and an increase in the distal sensory latency of the median nerve (more than 8.0 ms). The flexor retinaculum, or transverse carpal ligament, is usually divided on its ulnar aspect with complete release. This release may extend proximally into the

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volar carpal ligament, with an epineurotomy for thickened or scarred epineurium. Surgical treatment of carpal tunnel syndrome may be complicated by complex regional pain syndrome (reflex sympathetic dystrophy), scar formation, damage to the branches of the median ulnar nerve, tenosynovitis, flexor tendon adhesions, or bowstringing of tendons.

FIGURE 10.202 ● (A) Normal median nerve signal proximal to the carpal tunnel. Axial FS PD FSE image. (B) Hyperintense enlarged median nerve within the carpal tunnel between the proximal and distal carpal rows. Axial FS PD FSE image. Progressive narrowing of the carpal tunnel from proximal (C) to distal (D). Axial color cross-sections.

Excellent clinical results have been reported for endoscopic carpal tunnel release.¹³⁹ However, this procedure may be complicated by ulnar artery and median nerve laceration, partial laceration of the flexor tendons, and fracture of the hook of the hamate.¹⁴⁰ Incomplete release of the transverse carpal ligament may also occur with this technique. MR studies following carpal tunnel release may also demonstrate an increase in carpal canal volume.¹⁴¹ Carpal tunnel volume increases of up to 24% may be accompanied by a change in shape from a smaller oval to a circular configuration with an increased AP diameter. A smaller increase in volume was also shown in the mediolateral diameter.

Guyon's Canal/Ulnar Tunnel Syndrome

Pearls and Pitfalls

Guyon's Canal/Ulnar Tunnel Syndrome

Compression of the ulnar nerve may occur at the entrance to the ulnar tunnel, affecting the superficial branch (sensory) or the deep branch (motor).
The deep ulnar nerve supplies motor innervation to the hypothenar, interosseus, third and fourth lumbricals, and adductor pollicis muscles.
The superficial ulnar nerve provides sensory innervation to the skin of the hypothenar eminence and the fourth and fifth digits and motor innervation to the palmaris brevis.

Ulnar tunnel syndrome, also known as ulnar neuropathy or Guyon's canal syndrome, is characterized by numbness and

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tingling of the fifth (little) finger, the ulnar side of the fourth (ring) finger, and the palmar surface from irritation of the ulnar nerve in Guyon's canal. It is seen most frequently in young to middle-aged adults and is less common than median nerve compression or ulnar nerve entrapment at the elbow. It may be associated with sports injuries, and cyclists, golfers, and baseball players are at risk. Ulnar tunnel syndrome is also discussed in Chapter 12.

FIGURE 10.203 ● Carpal tunnel syndrome with enlarged hyperitense median nerve and thenar muscle denervation and atrophy. (A) Axial FS PD FSE image. (B) Axial PD FSE image.

The fibro-osseous ulnar tunnel (Guyon's canal) is formed by the pisiform and hamate bones (Fig. 10.205), contains the ulnar nerve and artery, and is located in the anteromedial aspect of the wrist (between the pisiform and the hook of the hamate). The ulnar nerve, which passes deep to the palmar carpal ligament and superficial to the flexor retinaculum (Fig. 10.206), divides into superficial and deep branches. The deep ulnar nerve provides motor innervation for the hypothenar, inlerosseus, third and fourth lumbricals, and adductor pollicis muscles. The superficial ulnar nerve provides sensory innervation to the skin of the hypothenar eminence and the fourth and fifth digits and motor function to the palmaris brevis. Anomalous muscles in the canal, the diameter of the ulnar nerve (normal mean diameter 3 mm), and the fibromuscular arch at the origin of the flexor digitorum brevis muscle are well characterized on axial MR images.

Etiology, Pathology, and Clinical Features

Compression of the ulnar nerve in Guyon's canal (Fig. 10.207) may be related to a variety of conditions or activities, including:

Sports activities (bicycling, baseball, and golf) that cause intermittent impaction or repetitive flexion/extension of the wrist
Soft-tissue tumors such as lipomas¹⁴² (Fig. 10.208)
Ganglion cysts (Fig. 10.209)
Scar tissue
Ulnar artery thrombosis or aneurysm (Fig. 10.210) from chronic repetitive trauma (hand tools that vibrate against the hypothenar eminence/the hypothenar hammer syndrome)
Carpal fractures (fractures of the hook of the hamate are most common) or distal radius fractures
Synovitis
Anomalous muscle belly
Arthritic changes

Compression at the level of the elbow is sometimes associated with median nerve findings of fixed motor deficits in the hand. A Martin-Gruber anastomosis (an ulnar-to-median nerve anastomosis

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present in 15% of the population) may produce anomalous motor and sensory findings, as may a Riche-Cannieu anastomosis, anastomosis between the deep branch of the ulnar nerve and the median nerve in the hand. Histologically there is evidence of increased pressure, impairment of the intraneural microcirculation, and ischemia.

FIGURE 10.204 ● Median nerve hyperintensity associated with acute thenar muscle denervation prior to fatty atrophy. Axial FS PD FSE images.

Patients present with gradual development of symptoms leading to difficulty opening jars, holding objects, or coordinating fingers while typing or playing a musical instrument. Typical signs and symptoms include:

Paresthesias followed by decreased sensation at the fourth and fifth fingers
Hand weakness
Sensory and/or motor changes depending on the pressure point
Positive Tinel's sign over the ulnar nerve
Positive Phalen's test with paresthesias in the fourth and fifth fingers
Electromyographic and electrodiagnostic testing may show denervation potentials in the interosseus muscle and motor nerve latency prolongation to the first dorsal interossei.

Compression at or proximal to the origin of the dorsal sensory branch of the ulnar nerve in the distal third of the forearm results in sensory deficits of the dorsoulnar aspect of the hand. Compression at the elbow may result in median nerve involvement, with fixed motor deficits and ulnar clawhand (caused by unopposed extensor digitorum communis and flexor digitorum profundus).

Classification

There are three distinct zones within Guyon's canal, and compression is classified according to the zone affected:

Zone I: Proximal to the bifurcation of the deep (motor) branch and the superficial (sensory) branch of the ulnar nerve. Compression in zone I produces motor and sensory deficits and is commonly caused by ganglion cysts or hamate hook fracture.

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Zone 2: The deep branch; compression produces motor deficits. Compression in zone 2 is also caused by ganglion cysts or fracture of the hook of the hamate.
Zone 3: The superficial branch; compression produces sensory deficits. Compression in zone 3 is related to ulnar artery aneurysm or thrombosis.

FIGURE 10.205 ● (A) Coronal color illustration showing ulnar tunnel or Guyon's canal and the relationship of the ulnar nerve. (B) T1-weighted axial image of Guyon's canal containing the ulnar nerve and artery at the level of the distal carpal row. Guyon's canal is formed by the pisiform bone, the flexor retinaculum, and a volar carpal ligament. The separate motor and sensory branches of the ulnar nerve are seen in zone I, deep to the volar carpal ligament. Division into the deep motor branch constitutes zone ll, and the superficial sensory branch constitutes zone lll. Compression of the ulnar nerve in zones I and III produces sensory findings, whereas compression in zones I and II produces motor findings.

FIGURE 10.206 ● Potential sites of ulnar nerve injury. Orange represents sensory fibers, green represents motor fibers, and mixed orange-green represents both. Corresponding ulnar-side palmar and dorsal cutaneous innervation is shown. Coronal and oblique color illustrations.

FIGURE 10.207 ● Ulnar tunnel syndrome with ischemia of the deep motor branch of the ulnar nerve. Coronal color illustration.

MR Appearance

Applications of MR imaging in the evaluation of the ulnar tunnel (or Guyon's canal) are similar to those for the carpal tunnel syndrome.¹⁴³ The lesion usually appears as a round to ovoid mass, and although the size is variable, less than 1 cm of the nerve is usually involved.

Key MR findings include:

Diffuse swelling
Enlargement of the ulnar nerve
Hyperintense signal within the ulnar nerve, best demonstrated on axial FS PD FSE or STIR images (see Fig. 10.208)
A round to ovoid mass (usually with hyperintense signal on FS PD FSE images)
A ganglion cyst
An aneurysm
Associated fracture
Anomalous muscle

T2* gradient-echo images are helpful in visualizing neural edema. Enlargement of Guyon's canal has been reported following carpal tunnel release.¹⁴¹

Treatment

Healing and recovery may take from several months to years. and older patients usually require longer periods of time. With severe compression, recovery may be incomplete. Management is initially conservative, including wrist splints and antiinflammatory medications. If there is a mass in the ulnar tunnel, it must be treated surgically. Resection of cysts and scar tissue results in improved sensation and decreased symptoms. Resection of the ligament that forms the roof of Guyon's canal (the palmar carpal ligament) may be needed to relieve pressure. Complications include nerve regrowth, which may be associated with pain lasting more than 6 weeks and requiring additional medication, massage, and therapy. Resection of the ligament forming the roof of Guyon's canal may cause scar tissue formation, resulting in recurrence of symptoms.

Arthritis

Pearls and Pitfalls

Arthritis

SLAC wrist, the most common pattern of degenerative arthritis of the wrist, develops in response to scaphoid rotation.
Initial changes of SLAC arthritis occur with degeneration of the proximal scaphoradial articulation, with subsequent development of capitolunate articular destruction.
Advanced SLAC represents complete destruction of the scaphoradial, capitotunate, and scaphocapitate joints. There is capitate impingement on the distal radius and narrowing of the hamate-lunate joint space. The radiolunate joint is not affected since it maintains smooth articular contact.

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Triscaphe arthritis is the second most common form of degenerative arthritis of the carpus.
A combination of SLAC and triscaphe arthritis represents the third most common form of degenerative arthritis.
Less common degenerative disorders include ulnolunate and lunotriquetral arthritis.

FIGURE 10.208 ● (A) Ulnar tunnel syndrome caused by extrinsic compression by a lipoma. Color axial section. (B) Axial T1-weighted image of lipoma within Guyon's canal encasing the ulnar nerve and vessels. (C) Hyperintense ulnar nerve on corresponding axial FS PD FSE image.

Conventional radiography has been the cornerstone of evaluation and follow-up of arthritides involving the hand, wrist, and elbow. The superior soft-tissue discrimination achieved by MR imaging, however, has proven useful in evaluating patients in both the initial and advanced stages of arthritis. MR imaging achieves noninvasive, accurate delineation of hyaline articular cartilage, ligaments, tendons, and synovium as distinct from cortical bone.¹⁹^,¹⁴⁴^,¹⁴⁵ Alterations in joint morphology or structure can also be identified on MR images before changes can be seen on standard radiographs.

Degenerative Arthritis

Joint space narrowing, loss of articular cartilage, subchondral sclerosis, and cyst formation characterize degenerative patterns of the carpus. Symptomatic disease is most commonly seen in middle-aged individuals, although older patients may be asymptomatic, and it occurs more often in males than in females. SLAC wrist is the most common form and triscaphe arthritis is the second most common form. SLAC wrist involves the scaphoradial, capitolunate, and scaphotrapezial, scaphotrapezoidal, and trapeziotrapezoidal articulations. Degenerative arthrosis is found in 5% of wrists. SLAC wrist is found in 55% of cases of degenerative wrist arthritis, and triscaphe arthritis accounts for 20% of cases of degenerative wrist arthritis. SLAC wrist and triscaphe arthritis appear together in 10% of cases of degenerative wrist arthritis.

FIGURE 10.209 ● (A) Axial color illustration showing a ganglion compressing the ulnar nerve. (B, C) Axial FS PD FSE images showing dorsal interosseus and adductor pollicis denervation secondary to a motor deficit of the deep branch of the ulnar nerve.

FIGURE 10.210 ● (A) Coronal color illustration (volar perspective) of ulnar artery aneurysm as an etiology of ulnar tunnel syndrome. (B) Maximum intensity projection MR image acquired post-contrast administration demonstrating a posttraumatic ulnar artery aneurysm. There is also an associated arteriovenous fistula resulting in local venous engorgement.

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Etiology, Pathology, and Clinical Features

High shear stresses over small contact surfaces are major contributors to the development of degenerative wrist arthritis. SLAC wrist develops from incongruent loading and degeneration across the radioscaphoid articulation, related to malalignment of the scaphoid, which may be caused by scaphoid fracture, nonunion, Kienböck's disease, or carpal fracture.¹⁴⁶ There is a progression from rotary subluxation of the scaphoid (Fig. 10.211), scapholunate ligament or periscaphoid dissociation, predynamic to dynamic to static rotary subluxation of the scaphoid, and finally radioscaphoid/SLAC or triscaphe arthrosis. SLAC degeneration is associated with the gradual collapse and loss of ligamentous support.

Triscaphe arthrosis is associated with load changes and articular pathology analogous to SLAC wrist and disruption in the ligamentous support of the scaphoid distally. Isolated scaphotrapezial involvement is more common than isolated scaphotrapezoidal involvement. Other locations of degenerative arthritis include the area between the distal ulna and the lunate and the lunotriquetral joints.¹⁴⁶

Pathologic findings in SLAC wrist vary depending on the stage of the disease:

Stage 1 (Fig. 10.212): arthrosis limited to the radial styloid-scaphoid articulation
Stage II: arthrosis of the entire radioscaphoid articulation
Stage III (Fig. 10.213): capitolunate arthrosis

Additionally, there may be destruction of the scaphocapitate articulation with capitate impingement (proximal migration on the radius) (Fig. 10.214) and secondary hamate-lunate joint narrowing. SLAC arthritis may be seen in association with scaphoid nonunion since there is preferential rotation of the distal scaphoid fragment in the radioscaphoid fossa. Rapid degenerative changes thus occur between the distal fragment of the scaphoid up to the fracture site.

Pathologic findings in triscaphe arthritis (Fig. 10.215) involve the scaphotrapezial articulation twice as often as isolated scaphotrapezoidal involvement. The trapezium and trapezoid migrate proximally.

Most patients present with wrist pain with activity, localized tenderness, a decreased grip strength in SLAC. and stiffness with dorsiflexion and radial deviation. Older patients may be asymptomatic. Scaphotrapeziotrapezoid arthritis is associated with carpal tunnel syndrome, radiopalmar ganglions, and de Quervain's tenosynovitis.

MR Appearance

The earliest changes seen in SLAC wrist involve spiking at the junction of the articular and nonarticular surfaces on the radial side of the scaphoid, sharpening at the radial styloid tip, and loss of cartilage. Early cartilage loss can be seen clearly on MR scans, and the low-signal-intensity initial changes in subchondral sclerosis of the radial styloid appear on MR images prior to any visible changes on conventional radiographs. Later in the disease, there is narrowing of the radioscaphoid joint, and the capitolunate joint begins to degenerate. Once the articular space between the capitate and lunate is lost, the hamate impinges against the lunate, and degeneration also occurs at this site. Key findings are:

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Sclerosis and narrowing with chondral loss between the radial styloid and scaphoid articulation
Sclerosis and narrowing involving the entire radioscaphoid articulation
Sclerosis and narrowing of the capitolunate joint
Loss of articular cartilage between the radial styloid and the dorsal pole of the scaphoid (in the setting of scaphoid nonunion)
Sclerosis or subchondral degenerative edema across the entire radioscaphoid articulation
Chondral loss in the capitolunate joint
Sparing of the radiolunate articulation, which can accommodate changes in scaphoid rotation and alignment
A fluid-filled gap between the scaphoid and lunate
Discontinuity of the scapholunate ligament
Degenerative cyst within the scaphoid, capitate, or distal radius.

FIGURE 10.211 ● (A) Normal radioscaphoid congruous joint surfaces. (B) The congruous joint surface contact between the scaphoid and radius is lost with rotational instability secondary to rotary subluxation of the scaphoid. There is an abnormal load transferred to the volar and dorsal margins of the radius and the center of the scaphoid. The rotation of the scaphoid thus accelerates the process of radioscaphoid joint degeneration. (C) Corresponding T1-weighted sagittal image of scaphoid rotation with secondary pattern of sclerosis between the distal radius and scaphoid.

FIGURE 10.212 ● Stage I SLAC with arthrosis of the radial styloid-scaphoid articulation. (A) Coronal color graphic. (B) Coronal T1-weighted image.

FIGURE 10.213 ● Stage III SLAC with arthrosis of the radioscaphoid articulation and capitolunate joint. (A) Color coronal graphic. (B) Coronal T1-weighted image.

FIGURE 10.214 ● Calcium pyrophosphate arthropathy of the wrist with findings of scapholunate dissociation, SLAC wrist with proximal migration of the capitate, ulnar translocation of the lunate, synovitis, and marrow edema involving the capitate and lunate on T1-weighted (A) and FS PD FSE (B) coronal images. Corresponding AP radiograph (C) demonstrates chondrocalcinosis (arrows) in the TFC complex and scapholunate ligament.

Characteristic findings in triscaphe arthritis include:

Subchondral sclerosis (scaphotrapeziotrapezoid arthrosis)
Sclerosis with chondral loss
Degenerative marrow edema (a late finding)
Proximal migration of the trapezium and trapezoid

Treatment

Without treatment there is progression of degeneration and ligament attenuation. Conservative approaches include immobilization and anti-inflammatory medications, but if symptoms are intractable, surgery, including wrist reconstruction for SLAC and arthrodesis for triscaphe arthritis, may be necessary.

FIGURE 10.215 ● Triscaphe arthritis with arthrosis and destruction of the trapezioscaphoid and trapezoidoscaphoid joints. There is disruption in the ligamentous support of the scaphoid distally. (A) Coronal color graphic. (B) Coronal T1-weighted image. (C) Coronal FS PD FSE image.

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Hamate-Lunate Impingement

In hamate-lunate impingement there is degenerative arthritis between a type II lunate with an extra facet (Fig. 10.216) and the proximal hamate. A type I lunate has no extra or medial facet. Hamate-lunate impingement is seen most commonly in individuals between 30 and 60 years of age.

An appreciation of the anatomy of both the lunate and the hamate is helpful in understanding the pathophysiology of this syndrome. The accessory facet is usually 1 to 6 mm and blunted to convex in shape. Relevant information on the lunate includes:

Located between the scaphoid radially and the triquetrum medially (ulnarly)
The deep concave distal surface articulates with the head of the capitate.
The convex proximal surface represents the lunate facet of the distal radius and the triangular fibrocartilage.
The medial surface is a large flattened facet for articulation with the triquetrum.
There is an extra medial lunate facet seen in type II lunate, which articulates with the hamate.
Radially there is a flattened facet for articulation with the proximal (medial) end of the scaphoid.
The distal articular surface is narrower than the proximal surface (i.e., the lunate is wedge-shaped).
The lunate is narrower dorsally.
Articular cartilage covers most of the lunate.
The lunate articulates with the radius, the capitate, the hamate, the scaphoid, and the triquetrum.

FIGURE 10.216 ● Type ll lunate (medial lunate facet) with sub-chondral erosion of the proximal pole of the hamate and accessory lunate facet. Coronal color illustration.

Relevant information on the hamate includes:
It is the most medial bone in the distal row.
The proximal surface is narrow and convex for the lunate articulation.
The distal surface articulates with the forth and fifth metacarpals via two facets.
The dorsal surface is triangular.
The palmar surface is the hook.
The lateral surface is the concavity of the body and the hook.
The ulnar surface articulates with the triquetrum.
The spiral orientation of the triquetrohamate joint facilitates motion between the proximal and distal carpal rows.

Etiology, Pathology, and Clinical Features

The type II lunate causes alteration of normal uniform loading, and the altered biomechanics leads to chondromalacia. There is increased pressure at the lunate fossa in wrist extension and ulnar deviation. In full ulnar deviation the hamate and lunate impinge on one another at articulation. The chondromalacia is secondary to impingement and abrasion of the hamate and lunate. Pathologic lesions include cartilage erosion, exposed bone, chondromalacia in the medial lunate facet and the proximal pole of the hamate, lunotriquetral ligament disruption, and scapholunate dissociation (less common than lunotriquetral ligament disruption). The facet size is 10% to 50% of the distal aspect of the lunate.

The clinical presentation is dominated by ulnar-sided wrist pain, particularly with radial and ulnar deviation of the wrist. Forced ulnar deviation intensifies the pain. The disorder is usually bilateral and symmetric and ranges from asymptomatic to focally tender over the proximal pole of the hamate. As mentioned, there is often associated lunotriquetral ligament instability.

MR Appearance

Chondral erosions between the accessory medial lunate facet and the proximal pole of the hamate are an obvious feature. Additional characteristic imaging findings are:

An extra medial lunate facet
Subchondral sclerosis of the proximal hamate or medial lunate facet (in advanced disease)

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Associated capitolunate arthrosis
Subchondral edema of the hamate (an uncommon finding)
Narrowing of the hamate-lunate joint space
Inhomogeneous signal intensity in the chondral surfaces of the medial lunate facet and the proximal hamate
Surface fibrillation, fraying, or full-thickness chondral defects (Fig. 10.217)
Four-corner arthritis (chondral degeneration in the proximal hamate, proximal capitate, radial distal triquetrum, and medial lunate facet)
Hamate or lunate marrow edema (unusual finding)
Small subchondral cystic changes in the proximal pole of the hamate
Subchondral bone loss in the proximal pole of the hamate and the medial lunate facet
Associated lunotriquetral ligament tear

Treatment

Hamate-lunate impingement is a slowly progressive process with a good clinical response to resection of the head of the hamate. Conservative approaches (rest, activity modification, and anti-inflammatory medications) may be tried first. Surgical resection of the head of the hamate may be performed as either an open or an arthroscopic procedure.

FIGURE 10.217 ● Medial lunate facet with chondromalacia between the medial facet and the proximal pole. The accessory facet may range in size from 10% to 50% of the length of the distal aspect of the lunate.

Rheumatoid Arthritis

Rheumatoid arthritis is a systemic autoimmune inflammatory disorder of unknown etiology, primarily affecting synovial membranes and articular surfaces. It affects 1% of the population, most commonly individuals from 25 to 60 years of age, with a peak incidence between 40 and 60 years of age. It is seen three times as often in females as in males. Serum antinuclear antibodies (ANA) are found in approximately 30% of patients.

Rheumatoid arthritis of the wrist characteristically involves the following structures:¹⁴⁷

Distal radioulnar joint
Ulnar and radial styloid

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Carpus (the scaphoid, triquetrum, and pisiform)
Radiocarpal, midcarpal, and carpometacarpal articulations
Metacarpophalangeal and proximal interphalangeal joints

Pathology and Clinical Features

Involvement varies from localized synovitis to involvement of the entire carpus (pancompartmental) and is characterized by erosions, joint space narrowing, soft-tissue swelling, and ulnar translocation. Soft-tissue swelling may be caused by joint effusion, edema, and tenosynovitis. Swan-neck and boutonnière deformities are frequent, and in advanced disease there are subluxations, dislocations, ulnar deviation in the metacarpophalangeal joints, and radial deviation in the radiocarpal articulation. Destructive changes include main en lorgnette (i.e., telescoping of the fingers), ulnar erosions, scapholunate dissociation, and distal radioulnar joint incongruity.

Pathologic changes include juxta-articular osteopenia (Fig. 10.218), bilateral, symmetrical joint involvement affecting the carpal joints, the metacarpophalangeal joints, and the proximal interphalangeal joints (Fig. 10.219), and pannus (a synovial mass resulting in marginal erosions at the junction of the articular cartilage and the bare area of bone). The chronic synovial-based inflammation can permanently damage tendons and may lead to capsular and ligamentous laxity and destruction of the TFC complex (Fig. 10.220). The tenosynovitis and swelling may lead to compression of the median or ulnar nerves, resulting in neuropathies (Fig. 10.221).

Disruption of the radioulnar joint with dorsal subluxation of the ulna (caput ulna syndrome) is caused by synovitis that results in stretching of ulnar carpal ligaments. There is pain, decreased range of motion, and dorsal subluxation of the ulna. The subluxed ulna may contact the extensor tendons, resulting in attrition and tearing.

FIGURE 10.218 ● Juxta-articular osteopenia with patchy marrow edema as shown on a coronal color graphic.

FIGURE 10.219 ● Ulnar deviation at the metacarpophalangeal joints is associated with radial deviation at the radiocarpal joint. Metacarpal head erosions are demonstrated. Soft-tissue swelling, marginal erosions (bare areas including the radial aspect of the second and third metacarpal heads), and joint deformities are common.

Histologically there is extensive synovial inflammation. hyperplasia of synovial cells, lymphocyte and plasma cell infiltration of the synovial membrane, and fibrinous exudates. Rheumatoid factor is a serum IgM antibody found in approximately 70% of patients. It is directed against the Fc fragment of IgG, and higher titers correlate with more severe disease.

There are a number of diagnostic criteria for the diagnosis of rheumatoid arthritis, and at least four of the following must be present to make the diagnosis:

Morning stiffness lasting more than 1 hour
Arthritis of three or more joints
Arthritis of hand joints
Symmetric arthritis
Positive serum rheumatoid factor
Rheumatoid nodules
Radiographic changes

Other common signs and symptoms include malaise, weakness, weight loss, myalgias, and fever of unknown origin. On physical examination there is joint swelling, bilateral involvement, erythema, pain with active and passive range of motion, tenderness to palpation, joint malalignment, and neuropathy in the median and/or ulnar nerve distribution.

Imaging Findings and MR Appearance

In patients with chronic rheumatoid disease, both plain film radiography

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and MR studies document the subluxations and erosions affecting the phalanges, carpals, metacarpals, and ulnar styloid. Radiographic findings are usually negative in the early stages of disease, although early soft-tissue swelling may be visible. Erosion of the ulnar styloid tip is often the first radiographic evidence of disease; other findings include:

Erosions at the distal radius and ulna (common)
Triquetrum and pisiform erosions
Marginal erosion at the radial aspect of the trapezium (common)
Juxta-articular osteopenia
Pancarpal progressive chondral loss, seen as gradual joint space narrowing or joint obliteration
Bony ankylosis, most common in the midcarpal compartment in late stages
The zig-zag deformity (radial deviation at the radiocarpal joint and ulnar deviation at the metacarpophalangeal joints)
Dorsal subluxation of the ulna (common)

FIGURE 10.220 ● Erosion of the ulnar styloid secondary to synovial inflammation of the prestyloid recess. (A) Coronal T2* gradient-echo image. (B) Axial FS PD FSE image.

MR imaging has become an important adjunct in diagnosing and monitoring patients with rheumatoid disease, including patient response to drug therapy. Gadolinium contrast MR imaging can be used to selectively enhance pannus tissue in synovitis involving the distal radioulnar joint; the ulnar styloid process; the radiocarpal, intercarpal, and metacarpophalangeal joints; and the flexor and extensor tendons.¹⁴⁸^,¹⁴⁹ When periarticular enhancement on MR imaging of the wrist or metacarpophalangeal and proximal interphalangeal joints ot the hand was used as a criterion for the diagnosis of early-stage rheumatoid arthritis, sensitivity was 100%, specificity 73%, and accuracy 89%.¹⁵⁰ Coronal FS gadolinium-enhanced T1-weighted images of the wrist and hand can be used to evaluate periarticular synovial inflammation as well as subchondral bone marrow edema. Synovial involvement of ligamentous structures frequently affects the ulnolunate and ulnotriquetral ligaments, the TFC complex, the distal radioulnar joint, the ulnocarpal meniscal homologue, the ulnar collateral ligament, the radioscaphocapitate ligament, the radioscapholunate ligament, the long radiolunate ligament, and the short radiolunate ligament.¹⁵¹ The differential diagnosis of rupture of the extensor tendon at the wrist includes metacarpophalangeal synovitis, posterior interosseus nerve palsy from rheumatoid disease of the elbow, and extensor tendon pathology overlying the metacarpal heads. With MR imaging, it is possible to identify rupture of the extensor pollicis longus tendon, which may be difficult to assess clinically if the function of the thumb is intact.¹⁵¹ MR imaging also allows identification of pannus involving the dorsal tendon sheaths and extensor tendons and effusion of the six extensor tendon compartments.¹⁵² TFC tears, dorsal displacement of the ulna, carpal tunnel pathology, and scapholunate dissociation are also assessed on routine coronal, axial, and sagittal studies.

FIGURE 10.221 ● Flexor digitorum profundus tendon rupture and associated synovitis of the flexor tendons are shown on a axial FS PD FSE image.

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Both T1 and T2 tissue relaxation times are prolonged in acute inflammation with edema and in joint effusion; therefore, both conditions demonstrate low signal intensity on T1-weighted images and hyperintensity on FS PD FSE images. Inflammatory edema may also extend into the subcutaneous tissues. In contrast, chronically inflamed tissue remains hypointense on both T1-weighted and FS PD FSE images. Adjacent areas of fluid collection demonstrate increased signal intensity on FS PD FSE acquisitions. Although the signal intensity of localized edematous or inflammatory tissue may be similar to that of synovial fluid, noninflammatory effusions in the wrist do not, when imaged on FS PD FSE, display an irregular pattern or focal distribution at multiple sites.

Cystic carpal erosions are better delineated on MR images than on corresponding AP radiographs. Destruction of cartilage and joint arthrosis is seen on PD-weighted and FS PD FSE images. Marrow changes (e.g., subchondral sclerosis), present on both sides of the joint or carpal articulation, help to differentiate arthrosis from intramedullary edema.

In patients with juvenile chronic arthritis with wrist involvement, early fluid collections along tendon sheaths, subar-ticular erosions, and cysts, as well as attenuated intercarpal articular cartilage, can be detected on MR images even when conventional radiographs are normal. Subluxations and areas of bone destruction are equally evident on MR images and on plain film radiographs.

Specific MR findings include:

Subchondral sclerosis, best appreciated on T1-weighted images
Early erosions with reactive marrow edema (Fig. 10.222)
Early joint effusions
Joint debris, visualized as signal inhomogeneity
Hypertrophied synovium, most frequently identified as intermediate signal intensity on FS PD FSE images
Tenosynovitis, hyperintense on FS PD FSE images
Partial tendon tears
Pannus (Fig. 10.223), which enhances vigorously after contrast administration

Treatment

Typically patients have slowly progressive joint destruction with intermittent flare-ups. The development of joint effusions with capsular distention and pain, large synovial cysts, tendinous tears and disruptions, cartilaginous and bony destruction, and median and ulnar neuropathies is not uncommon. Conservative treatment with pharmacotherapy and physical therapy is aimed at decreasing inflammation, delaying joint effusions, and preserving function. Surgery includes synovectomy and tenosynovectomy, repair of tendon ruptures (attachment to an adjoining tendon is preferable to segmental grafting), and arthroplasty or arthrodesis.

Miscellaneous Arthritides

In evaluating nonrheumatoid arthritic disease, we have had the opportunity to evaluate patients with psoriatic arthritis. Lyme disease, intraosseous sarcoid, hemophilia, calcium pyrophosphate deposition disease, and the more commonly found osteoarthritis. Wrist involvement is less common in primary osteoarthritis and secondary degenerative arthritis of the wrist is commonly seen in association with old trauma.

In psoriatic arthritis (Fig. 10.224), MR studies demonstrate destruction of the TFC with pancompartmental joint-space narrowing, erosions, scapholunate ligament disruption, and subchondral hypointense sclerosis in the carpus. Synovitis of the flexor carpi radialis tendon, the inferior radioulnar compartment, intermediate-signal-intensity inflammatory tissue, and dorsal subluxation of the distal ulna can be identified on T1-weighted and FS PD FSE axial images. In addition, the integrity of an artificial Silastic interphalangeal joint replacement

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(seen as an area of low signal intensity without artifact) can be assessed on coronal images. The site of fusion of the interphalangeal articulation of the thumb may be degraded by residual metallic artifact, despite prior surgical removal of fixation pins. In diffuse soft-tissue swelling of a single digit secondary to psoriatic arthritis, MR imaging may be successful in excluding the diagnosis of osteomyelitis.

FIGURE 10.222 ● (A) Flexor tendon tenosynovitis in association with rheumatoid disease on a coronal color illustration with inset. (B) A coronal FS PD FSE image demonstrating intermediate-signal-intensity pannus, carpal edema and erosions, TFC disruption, and scapholunate dissociation. (C) Axial FS PD FSE image showing tenosynovitis of the flexor pollicis longus tendon and distal radioulnar joint synovial inflammation.

MR imaging studies in Lyme arthritis of the wrist reveal information not available on conventional radiographs. Pockets of fluid collection, characterized by high signal intensity on FS PD FSE images, can be detected, as can the scalloped contour of a fluid interface adjacent to inflamed synovium. Joint deformities or cartilaginous erosions are not usually detected.

The hand is a predominant site of involvement in patients who have the relatively rare disorder of skeletal sarcoidosis. Conventional radiographs may demonstrate lytic changes characteristic of sarcoid in both the middle and distal phalanges. Although MR images may not provide any additional diagnostic information, the extent of soft-tissue granulomatous proliferation in the cystic defects and areas of cortical destruction are more accurately demonstrated on coronal and axial MR images. The noncaseating. granulomatous tissue typical of sarcoidosis demonstrates low to intermediate signal intensity on T1-weighted sequences and is intermediate to hyperintense on FS PD FSE images.

In hemophilia, acute hemorrhage into soft tissue may produce a fluid–fluid level. Higher-signal-intensity serum layers above the hemorrhagic sediment may also be seen. More subacute or chronic hemorrhage demonstrates hemosiderin (i.e. hypointense) signal intensity on T1-, FS PD FSE. or T2*-weighted images.

Intraosseous cysts (ganglions) (Fig. 10.225) of the wrist are hypointense on T1-weighted images and hyperintense on FS PD FSE or T2*-weighted or STIR sequences. These cysts, composed of fibrous tissue and mucoid material, are usually asymptomatic and present in a subchondral location.¹⁵³
In patients with calcium pyrophosphate deposition disease (see Fig. 10.214) the areas of intra-articular calcification are not satisfactorily demonstrated on T1-weighted images when compared with high-quality magnification radiographs. FS PD FSE and T2*-weighted images viewed at high contrast settings are useful in identifying areas of calcified crystalline depositions. The MR changes in calcium pyrophosphate deposition disease arthropathy include marrow hyperemia. widening of

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the scapholunate interval, proximal migration of the capitate, and joint space narrowing in the radiocarpal and metacar-pophalangeal joints. There is trapezioscaphoid involvement, with sparing of the distal radioulnar joint.¹⁵⁴ Calcium pyrophosphate deposition may also occur in the TFC complex and interosseous ligaments. Crystal deposition in ligaments can lead to their rupture. Thus, degenerative changes and SLAC wrist deformity can be seen in calcium pyrophosphate deposition disease.

FIGURE 10.223 ● Intermediate-signal-intensity pannus adjacent to synovial fluid in a rheumatoid wrist on a coronal T1-weighted image (A) and a coronal FS PD FSE image (B). (C) Axial FS PD FSE image demonstrates synovial thickening within the carpal tunnel and adjacent to the hamate.

The palmar involvement in Dupuytren's contracture has also been defined on MR imaging.¹⁵⁵ Dupuytren's contracture is a fibrosing condition of the hand frequently resulting in progressive flexion contractures of the fingers. Lesions include subcutaneous nodules at the level of the distal palmar crease and cords, parallel and superficial to the flexor tendons. These cords demonstrate low to intermediate signal intensity on T1-weighted images and low signal intensity on FS PD FSE images. The cords are composed of hypocellular

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dense collagen. Subcutaneous nodules demonstrate an inhomogeneous intermediate signal intensity on T1-weighted and FS PD FSE images. Less common hypocellular nodules demonstrate low signal intensity on both T1-weighted and FS PD FSE images. Dupuytren's contracture is also described in Chapter 11.

FIGURE 10.224 ● Psoriatic arthritis is classified into five subgroups based on the presence of acro-osteolysis of the distal interphalangeal joints, arthritis mutilans, symmetric polyarthritis, oligoarticular arthritis, and spondyloarthropathy. The subgroup with oligoarticular disease includes presentations of sausage-like tenosynovitis of the digits, as shown in this case. (A) Axial T1-weighted image. (B) T2*-weighted image.

Complex regional pain syndrom e (CRPS) (or reflex sympathetic dystrophy [RSD]) may demonstrate patchy or inhomogeneous bone marrow signal intensity similar to the early stages of osteopenia (Fig. 10.226).

Miscellaneous Abnormalities of the Wrist and Hand

In addition to changes seen in arthritis, other abnormalities including ganglions, tenosynovitis, tendon rupture, and changes of muscle denervation have been characterized on MR images of the hand and wrist.

Madelung's Deformity

Madelung's deformity is a developmental growth disturbance of the distal radial physis (Fig. 10.227) in which the distal radius epiphysis is triangular and medially tilted. Involvement can range from changes in the distal radius and ulna to changes in carpal morphology. It is a familial disorder with dominant inheritance and incomplete penetrance. It usually manifests during adolescence and is more common in females. Bilateral occurrence has been documented. There is a familial dysplasia profile, including hypoplasia of the radius and mesomelic dwarfism.

Etiology, Pathology, and Clinical Features

The deformity is caused by focal dysplasia of the distal radial physis and is considered a dyschondrosteotic form of mesomelic dwarfism. In addition to the usual familial condition, there is also a primary or idiopathic form, which is nonheritable.

Pathologic changes include bony lesions (dyschondrosteosis), dorsoulnar prominence of the ulnar head, radiopalmar displacement of the hand, tilting and bowing of the distal radius, and variable degrees of forearm shortening. In reverse Madelung's deformity the ulnar head is palmar and the wrist is arched dorsally. In extreme cases there is hypoplasia of the entire radius. In localized lesions involvement is primarily in the ulnopalmar zone of the distal radius with medial radial epiphysis deformity (tethering of the epiphysis proximally). There is a metaphyseal groove and a spike at the radiolunate ligament attachment to the area of growth retardation and an oblique radial attachment of the TFC.

A chevron carpus is an osseous lesion midway between Madelung's deformity and reverse Madelung's deformity. The clinical deformity is absent, but there is triangulation of carpus, which is wedged between the radius and the ulna.

Histologic studies show normal chondrocytes but abnormally arranged cell columns. The cambium layer cells of the periosteum stream from the periphery of the physis in the zone of Ranvier.

The most common presentation is wrist pain with deformity that may be apparent in infancy but may not appear until adolescence. The correlation between the severity of symptoms and imaging findings is poor. Additional signs and symptoms include:

Loss of motion
Weakness
Ligamentous stretching and carpal translation
Derangement of the distal radioulnar joint
Extensor tendon attrition over the deformed ulnar head in adults
Marked obliquity of the carpal tunnel associated with a susceptibility to median neuropathy in trauma

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Midcarpal joint involvement secondary to the triangular morphology of the carpus
Loss of supination and restriction of dorsiflexion and radial deviation

FIGURE 10.225 ● Large intraosseous ganglion of the scaphoid. There is a high association of intraosseous ganglions and soft-tissue ganglion cysts. Intraosseous ganglions are most common in the lunate. (A) Coronal T1-weighted image. (B) Coronal FS PD FSE image.

FIGURE 10.226 ● Patchy carpal marrow edema in response to injury with early clinical findings of complex regional pain syndrome on coronal color graphic (A), coronal T1-weighted (B), and corresponding FS PD FSE (C) images. Complex regional pain syndrome (CRPS; formerly known as reflex sympathetic dystrophy) may result from trauma or from neurologic or vascular insults. MR detects patchy osteoporosis as regions of nonspecific marrow edema. Diffuse osteopenia may have similar MR findings. CRPS type 1 occurs in response to an initiating noxious event, and there is no known nerve injury. CRPS type 2 or causalgia is related to a nerve injury but not necessarily limited to the distribution of the injured nerve.

FIGURE 10.227 ● (A) Madelung's deformity with medial angulation of the distal radial articular surface and triangulation of the carpus. Coronal color illustration. FS PD FSE (B) images of Madelung's deformity with proximal migration of the lunate (triangulation of the carpus), medial angulation of the distal radius, and oblique orientation of the TFC.

MR Appearance

The most obvious imaging finding is the triangular shape and medial tilt of the distal radius epiphysis. Other MR findings include:

Ulnar angulation of the distal radial articular surface
A dorsoulnar configuration of the ulnar head (dorsally prominent ulnar head)
Bowing of the radius
A physeal lesion at the palmar ulnar aspect of the distal radial physis
A thickened radiolunate ligament attached to the distal radial physis
Development of a groove and osseous spike at the ulnar aspect of the metaphyseal-diaphyseal junction from the tethering effect of the radiolunate ligament
Oblique radial TFC attachment
Lunate ischemia is sometimes seen.
Chevron carpus (mid-ulnar zone dyschondrosteosis)
Advanced dyschondrosteosis with lack of proximal lunate support by the radius

Treatment

Patients show progressive radiologic deterioration, and bracing is used to control symptoms. Eventually the distal radius is turned in an ulnar and palmar direction. The carpus and hand appear volar to the forearm and the ulna shows dorsal subluxation. Surgery is indicated for patients with persistent pain, loss of normal anatomy, grip weakness, and severe deformity. Procedures include resection of the distal ulna (the Darrach procedure), distal radioulnar joint fusion and ulnar osteotomy (the Sauvé-Kapandji procedure), open or closed wedge osteotomy of the radius, placement of external fixators, epiphysiodesis of the distal ulna or radius, and radiocarpal and total wrist fusion. Prophylactic exci-sion of the physeal bar has been performed in symptomatic adolescents.

Ganglion Cysts

Cystic swellings overlying a joint or tendon sheath are referred to as ganglions or ganglia and are thought to be secondary protrusion of cystic mucinous joint fluid.¹⁵⁶^,¹⁵⁷^,¹⁵⁸^,¹⁵⁹ In the wrist they tend to be oval masses, with a narrow stalk extending from the origin, and vary in size from 5 mm to 2 cm (and increase in size with activity). They are found in the following locations:

Dorsal scapholunate interval (Fig. 10.228)
Volar (palmar) radiocarpal joint
Dorsal retinaculum of the first extensor component
Carpal tunnel
Guyon's canal
Triscaphe joint
Ulnocarpal joint
Second metacarpal-trapezial joint

Ganglions are the most common soft-tissue mass of the wrist, representing 50% to 70% of all soft-tissue masses of the wrist and hand. Approximately 60% to 70% of ganglions are dorsal, and they tend to occur in the second, third, and fourth decades. The incidence of radiocarpal palmar ganglions is approximately 20%, and ganglions in this location are most likely to occur in the fifth, sixth, and seventh decades. There is a predilection for females.

Etiology, Pathology, and Clinical Features

Scapholunate ligament ganglions have a membranous and/or dorsal component origin (Fig. 10.229). Stress forces are centered between the scaphoid and lunate and joint fluid is pumped through a one-way valve between collagen bundles when there is a weakness in the dorsal capsule. Palmar radiocarpal ganglions are found near the origin of the radiocarpal ligament and arise from the triscaphe joint.

FIGURE 10.228 ● Common location of a ganglion cyst relative to the dorsal scapholunate interval. Coronal color illustration.

Pathologic findings include cystic mucinous joint fluid in a pseudocapsule. Ganglion protrusion through the scapholunate ligament may or may not be confined deep to the radiocarpal ligament, and there may be protrusion through the dorsal wrist capsule. The masses are palpable, firm, and smooth and may be multilobular. Dorsal ganglions are located where the dorsal interosseus nerve approaches the joint capsule and the cyst connects to the joint capsule or tendon sheath via a narrow stalk. Palmar radiocarpal ganglions protrude along the flexor carpi radialis tendon sheath. Retinacular ganglions are associated with a hypertrophic retinaculum superficial to stenosing tenosynovitis (de Quervain's). Guyon's canal ganglions are located at the weak region in the pisohamate ligament. Histologic findings include collagen fiber breakdown products, intercellular mucin, microscopic mucinous pools that coalesce and expand, dissection through subcutaneous tissue, a pseudocapsule of compacted fibrous tissue, and a capsule lining of compressed collagen fibers and flat nonendothelial (nonsynovial) cells.

Patients present with a localized soft-tissue mass that may be accompanied by localized pain (with dorsiflexion) and weakness. There are neurologic findings only if the carpal tunnel or Guyon's canal is involved. The ganglion is soft to firm in consistency and does not move with the adjacent tendon. There may be an associated intraosseous carpal ganglion. Both size and symptoms may increase after activity. Allen's test and/or Doppler testing will confirm the patency of the radial artery.

MR Appearance

The finding of a homogeneous fluid-filled mass in communication with the scapholunate interval is the most common finding on MR images. Ganglion cysts generate low signal intensity on T1-weighted images and high signal intensity on T2-weighted (FS PD FSE) images. Fibrous septations may cause loculation of the ganglion. Even with infiltration or edema of adjacent tissues, these lesions are well demarcated on MR imaging. Intercarpal communication of a ganglion is more frequent than communication with the radiocarpal joint. MR imaging is used to identify the joint or tendon of origin and to exclude other soft-tissue masses, such as neoplasms, when an accurate preoperative clinical assessment is difficult and wrist arthrography is not satisfactory. Wrist ganglions may be associated with the first carpometacarpal joint, the scaphotrapeziotrapezoid joint, the volar or dorsal wrist capsule, or the flexor carpi radialis tendon. The stalk of the ganglion frequently can be discerned on MR images. Dorsal carpal ganglions, including the occult dorsal carpal ganglion, are effectively evaluated by MR imaging.¹⁶⁰ MR imaging may show an origin from the dorsal scapholunate ligament.¹⁶¹ Contrast-enhanced imaging may be used to confirm the cystic contents of a ganglion (peripheral enhancement) versus a soft-tissue neoplasm.

Key MR findings include:

Soft-tissue cystic mass (Fig. 10.230), which may be unilocular or multiloculated (Fig. 10.231)
Subcutaneous tissue adjacent to the mass is normal.

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Arthrosis of the scaphotrapezial or radioscaphoid articulations
Scapholunate diastasis on coronal images
Narrow stalk in communication with the main cyst, which may be difficult to visualize on T1-weighted images but is conspicuous and hyperintense on FS PD FSE or STIR images
Stalk extension through the joint capsule with an elongated pedicle allows cyst presentation away from its point of origin (e.g., cysts originating from the scapholunate interval may be ulnar to the extensor tendons).
Hypointense capsule may be seen on FS PD FSE images.
Inhomogeneity of cyst related to mucin content as appreciated on FS PD FSE images
Small carpal tunnel ganglions are frequently traced to the scaphotrapeziotrapezoid joint.
Secondary compression of the median nerve
Cyst communication with its adjacent tendon sheath
Intraosseous carpal ganglions

FIGURE 10.229 ● (A) A dorsal ganglion may be associated with a sprain or tear of the dorsal and/or membranous fibers of the scapholunate ligament complex. Coronal color graphic. (B, C) A scapholunate ligament dorsal component sprain associated with radial extension of an associated dorsal ganglion. (B) Coronal FS PD FSE image. (C) Axial FS PD FSE image.

Treatment

Ganglion cysts vary considerably in size and production of discomfort. Almost half resolve without any treatment. Conservative treatment, including manual rupture, cyst wall puncture, aspiration and steroid injection, is complicated by a relatively high recurrence rate, especially for palmar

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ganglions. Surgical treatment consists of excision of the ganglion, including the stalk.

FIGURE 10.230 ● Direct extension of dorsal ganglions through the dorsal fibers of the scapholunate ligament. Synovial fluid is pumped between collagen bundles in weak areas in the dorsal capsule. (A) Coronal T1-weighted image. (B) Coronal FS PD FSE image.

Giant Cell Tumors of the Tendon Sheath

Giant cell tumors of the tendon sheath (GCTTS) (Fig. 10.232), also referred to as extra-articular pigmented villonodular synovitis, histiocytomas, and benign synoviomas, are small (usually 0.5 to 5 cm) nonneoplastic benign tumors of giant cells found in the vicinity of joints, usually in the hand. The localized type is the second most common soft-tissue mass of the hand, after ganglions. A rare diffuse form is the soft-tissue counterpart of pigmented villonodular synovitis (Fig. 10.233). The most common locations are the volar aspect of the hand and fingers adjacent to the distal interphalangeal joint. Two thirds of the masses are located on the volar aspect of the fingers, most commonly the index and long finger. They are primarily seen in individuals 30 to 50 years of age (peak incidence is 40 to 50 years) and are rare in those under 10 or over 60 years of age. The female-to-male ratio is 3:2, and they are slightly more common in the right hand.

Etiology, Pathology, and Clinical Features

The most likely cause and best-accepted theory for GCTTS is that it is a reactive or regenerative hyperplasia associated with inflammatory process. Other causes have been proposed, including trauma, disturbed lipid metabolism, osteoclastic proliferation, infection, vascular disturbances, immune mechanisms, inflammation, neoplasia, and metabolic disturbances.

Pathologic findings include a firm, well-circumscribed lobulated mass with a mottled appearance, varying in color from grayish-brown to yellow-orange. They are nodular with a villous morphology. Histologically, they are characterized by mononuclear rounded or polygonal cells (lipid-laden histiocytes and multinucleated giant cells). The number of giant cells present varies, and hemosiderin-containing xanthoma cells may be found in the periphery of the lesion.

Patients present with a painless, slow-growing mass present for weeks to years. The mass may cause occasional distal numbness or limited function of the digit due to the size of the lesion. Unlike ganglions, the mass does not transilluminate.

MR Appearance

A soft-tissue mass with hypointense, intermediate, and hyperintense areas is apparent on FS PD FSE images (Fig. 10.234). Intravenous contrast administration produces intense enhancement and variable inhomogeneity (Fig. 10.235).

Other MR findings include:

Fibrous septations and lobulations
Convex bowing or bulge toward the skin from the tendon sheath
Flexor or extensor tendon-related location
Extension in the transverse and longitudinal planes
Origin may be deep to the tendon (between the tendon bone).
Foci of hemosiderin (hypointense on T1-, PD-, or FS PD FSE images) may be peripheral (sometimes clumped) or found throughout the lesion.

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A sharply defined interface without reactive edema of the adjacent subcutaneous tissue
Adjacent osseous erosion (unusual but can occur)
Greater long-axis growth is characteristic.
Minimal associated fluid is observed adjacent to the lesion.

FIGURE 10.231 ● Distal and dorsal extension of a multiloculated and multilobular scapholunate ligament ganglion, which has protruded through the dorsal wrist capsule. The ganglion connects to the joint capsule through a narrow stalk. These ganglions have a nonsynovial capsular lining of compressed collagen fibers and flat nonendothelial cells. (A) Axial FS PD FSE image. (B) Coronal FS PD FSE image.

FIGURE 10.232 ● (A) Coronal graphic and sagittal inset of a giant cell tumor of the flexor tendon sheath. Characteristic lobulations and well-circumscribed fibrous morphology are shown. (B, C) Localized form of giant cell tumor, or extra-articular pigmented villonodular synovitis, involving the radial dorsal aspect of the third digit (long finger) proximal to the distal interphalangeal joint. The majority (up to two thirds) of giant cell tumors are located in the volar aspects of the fingers and usually involve the index and long fingers. (B) Axial T1-weighted image. (C) Axial FS PD FSE image.

FIGURE 10.233 ● Rare diffuse form of extra-articular giant cell tumor of the tendon sheath similar to pigmented villonodular synovitis. Axial FS T1-weighted contrast-enhanced MR image.

FIGURE 10.234 ● Volar presentation of characteristic MR findings of giant cell tumor of the tendon sheath with intermediate and hyperintense regions within the lesion. Corresponding histology demonstrates histiocytes and multinucleated giant cells. Hemosiderin-containing xanthoma cells occur in the periphery of the lesion and are best appreciated using T2* gradient-echo techniques. (A) Coronal T1-weighted image. (B) Axial T1-weighted image. (C) FS PD FSE image.

FIGURE 10.235 ● Typical intense contrast enhancement of a giant cell tumor shown between the flexor tendons and phalanx. Axial FS T1-weighted image.

Treatment

GCTTS is characterized by progressive slow growth. In the late stages there is exuberant, heavily pigmented villous synovial overgrowth and osseous erosions related to lesion hypervascularity. Treatment is surgical; procedures include marginal excision, complete excision (difficult), and possible bony débridement. Complications include the development of satellite lesions in incomplete resections, since puncturing the lesions may result in seeding of the operative bed. Even with careful dissection, recurrence rates are high, and sometimes tendon reconstruction is necessary. No malignant degeneration has been reported.

Tenosynovitis, Tendon Rupture, and Muscle Denervation

Tenosynovitis and capsular synovitis may occur together as part of the spectrum of rheumatoid disease, or they may exist as isolated conditions with a traumatic or infectious etiology. Thickening, swelling, or fluid associated with an irritated synovial tendon sheath may be demonstrated on MR images. An edematous sheath appears as a rim of increased signal intensity on FS PD FSE images. Both flexor and extensor tenosynovitis may occur without a history of infection. Carpal distention may be evident in the small interphalangeal or metacarpal joints when small amounts of synovial fluid accumulate.

De Quervain's Tenosynovitis

Pearls and Pitfalls

De Quervain's Tenosynovitis

Tendinosis and tenosynovitis of the abductor pollicis longus and extensor pollicis brevis are assessed at the level of the radial styloid on axial MR images.
The striated appearance of the abductor pollicis longus is related to enlargement of tendinous slips. Longitudinal splitting is more common in the abductor pollicis longus.
A longitudinal septum may divide the abductor pollicis longus and extensor pollicis brevis, creating a subcompartment for the extensor pollicis brevis.

De Quervain's tenosynovitis, also know as washerwoman's sprain and stenosing tenosynovitis, is a tenosynovitis and tendinitis of the first dorsal compartment affecting the abductor pollicis longus and the extensor pollicis brevis tendons at the level of the radial styloid (Fig. 10.236). There is variable enlargement of the tendons within the fibro-osseous tunnel.

An understanding of the relevant anatomic structures helps to understand the pathophysiologic processes. The first extensor compartment is directly over the radial styloid process. The fibro-osseous tunnel is a tubular passageway, 2.5 cm in length, formed by a groove in the radial styloid and the overlying extensor retinaculum. The large abductor pollicis brevis and the smaller extensor pollicis brevis pass through the fibro-osseous tunnel, which represents the radial side of the anatomic snuffbox. Important anatomic variations include complete compartmentalization of the extensor pollicis brevis and multiple slips of the abductor pollicis brevis.

The first dorsal compartment serves as a pulley to align the tendons with the dorsum of the thumb proximal to the first metacarpal insertion of the abductor pollicis brevis and the proximal phalangeal insertion of the extensor pollicis brevis. The superficial branch of the radial nerve overlies the first dorsal extensor compartment.

Etiology, Pathology, and Clinical Features

The abductor pollicis brevis and extensor pollicis brevis tendons are susceptible to tendinitis from repetitive wrist and hand motions (chronic micro-overuse).¹⁶² Activities such as grasping, pinching, and wringing lead to increased friction and inflammation and the tendons enlarge in the fibro-osseous tunnel at the level of the radial styloid. Trauma, such as a direct blow or fall onto the thumb, may also cause scarring with friction and inflammation. Participation in athletics, especially activities requiring forceful grasp and repetitive use of the thumb in ulnar deviation (e.g., racquet sports, golf [hyperabduction during the swing], fly fishing, and javelin and discus throwing, puts individuals at risk. In fact, de Quervain's tenosynovitis is the most common stenosing tenosynovitis in athletes. Eventually the tendons stretch and the tunnel approach angle increases with ulnar deviation.

Pathologic findings include tendon inflammation and enlargement. In 20% to 30% of patients a longitudinal septum divides the abductor pollicis brevis and extensor pollicis brevis.

Clinically, there are tenderness and swelling at the radial styloid and a positive Finkelstein's test (radial styloid pain and passive ulnar deviation of the wrist with adduction of the thumb). Pain is increased with wrist and thumb motion and passive ulnar deviation and may radiate to the radial side of the forearm. There is sometimes a tender nodule over the radial

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styloid and point tenderness over first dorsal compartment. Triggering or crepitus may also occur.

FIGURE 10.236 ● De Quervain's tenosynovitis involving the abductor pollicis longus and extensor pollicis brevis at the level of the radial styloid. (A) Oblique color graphic. (B) Axial FS PD FSE image.

MR Appearance

Edema and fluid associated with the first extensor compartment is the most common finding. MR imaging also shows enlargement or thickening of the abductor pollicis brevis tendon sheaths. There is hyperintense fluid within the tendon sheath, and the involved tendons are also thickened. There may be intrasubstance hyperintensity as tendinitis develops.¹⁶³ The MR findings depend on whether there is tenosynovitis or tendinitis/tendinosis. In tenosynovitis, key MR findings include:

Fluid signal intensity in the distended tendon sheath and surrounding extensor pollicis brevis and abductor pollicis brevis
Debris within the sheath
Effacement of subcutaneous fat radial to the extensor pollicis brevis and abductor pollicis brevis
Hyperintense adjacent subcutaneous fat on FS PD FSE images
Intermediate signal in chronic changes on FS PD FSE images

In tendinitis/tendinosis, key findings include:

Central or eccentric intermediate signal in the grossly enlarged extensor pollicis brevis and abductor pollicis brevis tendons on T1- and PD-weighted images (Fig. 10.237)
Tendon degeneration (displays intermediate signal intensity on FS PD FSE images unless associated with a hyperintense longitudinal split)
Enlargement of the first extensor compartment tendons from medial to lateral on coronal images and in cross-sectional diameter on axial images
Maximum tendon enlargement is at and immediately distal to the radial styloid.
Longitudinal splitting of the tendon is more common in the abductor pollicis brevis tendon.
A septum between the tendons (forming a subcompartment for the extensor pollicis brevis)
Striation of abductor pollicis brevis related to enlargement of multiple slips

Treatment

Without treatment, fibrosis develops within the tendon sheath, leading to trigger finger and limitation of motion. The majority (80%) of patients improve with conservative treatment including anti-inflammatory medications, rest, cessation of aggravating activities, splinting (thumb spica splint), steroid injections (often producing excellent results), and physical therapy. Surgery is reserved for recalcitrant cases and includes decompression of the common tendon sheath and lysis of a dividing septum if present. Complications include perineural fibrosis of the superficial radial nerve. Inadequate decompression leads to tendon instability and adherence to scar tissue.

FIGURE 10.237 ● De Quervain's stenosing tenosynovitis (arrow) with inflammation of the abductor pollicis longus (apl) and extensor pollicis brevis (epb) tendons of the first extensor compartment. Inflammation is associated with these enlarged tendons in the fibro-osseous tunnel at the level of the radial styloid (R). Increased signal intensity in the tendon sheath (tenosynovitis) and tendon (tendinitis) coexist in this case. (A) T2*-weighted coronal image.(B) T1-weighted axial image.

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Extensor Carpi Ulnaris Tendinitis and Dysfunction

Pearls and Pitfalls

Extensor Carpi Ulnaris Tendinitis and Dysfunction

The subsheath of the extensor carpi ulnaris forms the fibro-osseous tunnel, attaches to the ulnar styloid and ulnar head, and merges with the capsule of the distal radioulnar joint and the TFC complex.
The position of supination and ulnar deviation reproduces extensor carpi ulnaris instability. Extensor carpi ulnaris relocation occurs with pronation and radial deviation.
Longitudinal splitting of the extensor carpi ulnaris tendon is characterized by hyperintense signal intensity and is associated with tenosynovitis.

Extensor carpi ulnaris tendinitis is an inflammation of the synovial lining of the extensor carpi ulnaris tendon sheath from chronic strenuous use (Fig. 10.238). It is most commonly seen on the dorsal ulnar aspect of wrist and the sixth extensor compartment and is the second most frequent site of stenosing tenosynovitis in the upper extremity.

An understanding of the anatomy of the sixth extensor compartment is helpful. The sixth compartment contains the extensor carpi ulnaris tendon and sheath and contributes to the stability of the ulnar aspect of the wrist. A separate subsheath, which attaches to the ulnar styloid and head, forms the fibro-osseous tunnel, and the fibro-osseous tunnel maintains the extensor carpi ulnaris position during rotation. A septum anchors the fibro-osseous tunnel to the radius dorsally, and the retinaculum attaches to the volar aspect of the pisiform and triquetrum. The subsheath merges with the capsule of the distal radioulnar joint proximally and the TFC complex distally.

Etiology, Pathology, and Clinical Features

Repetitive activities using ulnar deviation cause reactive extensor carpi ulnaris tenosynovitis (Fig. 10.239), resulting in recurrent subluxation and loss of sixth compartment integrity. Primary extensor carpi ulnaris tenosynovitis is usually associated with acute trauma, repetitive wrist motion, or ulnar styloid nonunion with a roughened surface. Athletes who participate in racquet sports, baseball, and golf are all at higher risk. There is also an association with rheumatoid arthritis, with accompanying synovial cysts and subluxation/dislocation.

In supination the extensor carpi ulnaris tendon is dorsal in position (normal), and in pronation the extensor carpi ulnaris tendon is ulnar in position (normal). In extensor carpi ulnaris subluxation or dislocation, supination and ulnar deviation reproduces extensor carpi ulnaris instability (Fig. 10.240). Pronation and radial deviation relocates the extensor carpi ulnaris tendon. Tendon degeneration is characterized by decreased collagen content, loss of collagen cross-linking (causing tendon stiffness), and decreased resistance to shear force.

Clinically the patient presents with pain dorsally at the distal ulna, swelling, and crepitus. Traumatic rupture of the extensor carpi ulnaris subsheath represents the painful subluxation syndrome with painful snapping on pronation and supination. Extensor carpi ulnaris subsheath rupture and extensor retinaculum disruption are seen in chronic dislocation with forced supination, palmarflexion, and ulnar deviation.

FIGURE 10.238 ● (A) Extensor carpi ulnaris tendinitis represents an inflammation of the synovial lining of the extensor carpi ulnaris and is frequently associated with intrinsic tendon degeneration. Color coronal illustration and axial inset. (B) Longitudinal split of extensor carpi ulnaris tendon occurs as the extensor carpi ulnaris tendon becomes stiff and has a decreased resistance to shear forces. Axial FS PD FSE image.

FIGURE 10.239 ● Extensor carpi ulnaris tenosynovitis and tendinosis. Tendon degeneration is associated with a decrease in collagen content. (A) Axial T1-weighted image. (B) Axial FS PD FSE image.

FIGURE 10.240 ● (A) Normal position of the extensor carpi ulnaris tendon in partial supination. (B) Dislocation of the extensor carpi ulnaris in the position of maximal supination. Supination and ulnar deviation reproduce extensor carpi ulnaris instability, and extensor carpi ulnaris relocation occurs with pronation and radial deviation. (C) Extensor carpi ulnaris subluxation secondary to chronic synovial inflammation displacing the extensor carpi ulnaris in an ulnar direction in the neutral position of the ulna (partial supination). Rupture of the extensor carpi ulnaris subsheath results in a painful subluxation syndrome. (A, B) Axial FS PD FSE images. (C) Axial FS PD FSE image.

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Classification

Extensor carpi ulnaris tendinitis is classified according to the presence of tenosynovitis (primary or reactive), tendinosis, longitudinal splitting, or rupture (Fig. 10.241).

MR Appearance

Distention of the tendon sheath with fluid is the most common finding. Other characteristic MR findings are:

Fluid within the extensor carpi ulnaris tendon sheath (see Figs. 10.238, 10.239, and 10.241)
Thickening of the tendon sheath
Increased cross-sectional diameter of the extensor carpi ulnaris tendon
Fraying of the tendon margins
Tendon degeneration
Extensor carpi ulnaris subluxation or dislocation
Intermediate-signal-intensity fluid on FS PD FSE images in chronic tenosynovitis
Intermediate signal on FS PD FSE images in tendinosis/degeneration
Longitudinal splitting
Replacement of tendon by fluid signal in complete extensor carpi ulnaris rupture
Foci of calcification
Inflamed synovium, which enhances after administration of intravenous contrast

Treatment

Most patients are able to return to sports activities with a range of motion that is approximately 70% of the opposite extremity. The prognosis is good with early and adequate treatment. Conservative treatment for extensor carpi ulnaris

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tendinitis includes diagnostic and therapeutic injection of lidocaine and cortisone, splinting, nonsteroidal anti-inflammatory agents, and the RICE protocol (rest, ice, compression, and elevation). Conservative treatment for acute extensor carpi ulnaris rupture is application of a long-arm cast in full supination and neutral wrist flexion/extension. Surgery is necessary for chronic or nonresponsive conditions. Extensor carpi ulnaris tendinitis with progressive fibrosis of the sixth compartment requires surgical release, and traumatic rupture of the extensor carpi ulnaris is treated with reconstruction of the retinaculum.

FIGURE 10.241 ● Extensor carpi ulnaris rupture as an endstage in the process of tenosynovitis, tendinosis, and longitudinal splitting. Axial FS PD FSE image.

Miscellaneous Tendinopathies

Flexor Carpi Radialis Tendinitis

The flexor carpi radialis musculotendinous unit (Fig. 10.242) can also be evaluated on MR imaging. Proximal to the radiocarpal joint, the average length of the flexor carpi radialis musculotendinous unit is 15 cm. Proximal to the radial styloid the average tendon length is 8 cm. The flexor carpi radialis tendon occupies a fibro-osseous tunnel at the proximal border of the trapezium.¹⁶⁴^,¹⁶⁵^,¹⁶⁶ A thick septum separates the flexor carpi radialis from the carpal tunnel. The tendon occupies 90% of the space within its tunnel and is in direct contact with the roughened surface of the trapezium. The tendon is in immediate proximity to the distal radius, the scaphoid tubercle, the scaphotrapeziotrapezoid joint, and the carpometacarpal joint of the thumb. This tendon is potentially vulnerable to primary stenosing tenosynovitis and secondary injury with tendinitis associated with distal scaphoid fracture, scaphotrapeziotrapezoid arthritis, and carpometacarpal joint arthritis. Trauma or degeneration of the tendon within the constrained tunnel may be the predisposing event in the development of flexor carpi radialis tendinitis.

Intersection Syndrome

In the intersection syndrome (Fig. 10.243) there is tenosynovitis of the radial wrist extensors, the extensor carpi radialis longus, and the extensor carpi radialis brevis of the second dorsal compartment. The condition also affects the extensor pollicis brevis and the abductor pollicis longus, causing pain and swelling of these muscle bellies. It is characterized by pain and swelling in the distal dorsoradial forearm, approximately 5 cm proximal to Lister's tubercle. Symptoms occur where the first extensor compartment tendons (the abductor pollicis brevis and extensor pollicis brevis) cross over the second extensor compartment tendons (the extensor carpi radialis longus and extensor carpi radialis brevis). Repetitive wrist motion and trauma may lead to tenderness and crepitus.

MR is helpful in establishing the diagnosis. Peritendinous edema around the first and second extensor compartment tendons, extending proximally from the crossover point, is the most characteristic finding. Changes may be subtle, however, and difficult to identify.

Pathology of the Finger and Thumb

A more detailed discussion of MR imaging of the fingers, including normal anatomy, techniques and protocols, and additional pathologic conditions, can be found in Chapter 11.

Ligament Pathology

Ligamentous injuries of the fingers (Fig. 10.244) and thumb (Fig. 10.245) include disruptions of the capsular ligaments, frequently involving the metacarpophalangeal and proximal interphalangeal joints of the fingers¹⁶⁷ and the metacarpophalangeal and interphalangeal joint of the thumb. The proximal interphalangeal joint is a relatively rigid hinge joint and is therefore susceptible to injury through transmission of lateral and torque stress. Masson et al.¹⁶⁷ have used MR imaging to identify the separate components of the proper and accessory collateral ligaments of the thumb and finger metacarpophalangeal joints. The more volar accessory component of the collateral ligament inserts onto the lateral margin of the volar plate and is identified deep to the proper collateral ligament on coronal MR images. The volar plate capsular thickening extends from its strong fibrocartilage attachment to the base of the proximal phalanx to a thinner attachment onto the neck of the metacarpal. Volar plate injuries, which are caused by hyperextension, may result in hyperextension or flexion deformities of the joint. Initial treatment for these injuries is short-term splinting in 25 of flexion. The extensor mechanism of the fingers can also be evaluated with axial and sagittal MR images.¹⁶⁸

Ulnar Collateral Ligament Tears of the Thumb

FIGURE 10.242 ● (A) Flexor carpi radialis tenosynovitis (arrows) is hyperintense on an FS PD FSE axial image at the level of the proximal carpal row. (B) The vulnerable area of fibro-osseous tunnel narrowing (white arrow) occurs beneath the prominent trapezial crest (black arrow). Since the tendon sheath forming the rigid fibro-osseous canal narrows and ends at the level of the trapezium (T), MR findings of tendinitis or tenosynovitis are seen proximal to this location. Axial T1-weighted image. (C) Flexor carpi radialis partial tear with tendon cross-sectional enlargement visualized proximal to the trapezium. Axial T1-weighted image.

FIGURE 10.243 ● Area where tenosynovitis of the second dorsal compartment occurs in intersection syndrome. Pain and swelling usually occur proximal to the wrist as inflammation occurs where the muscle belly of the abductor pollicis longus and extensor pollicis brevis cross the common wrist extensors of the second dorsal compartment. Coronal color graphic.

FIGURE 10.244 ● (A) Index metacarpophalangeal joint with direct extension of hyperintense joint fluid across a torn proximal attachment of the ulnar collateral ligament (arrows). There is disruption of both the proper (p) and accessory (a) components of the collateral ligament. T2*-weighted coronal image. (B) Correspond-ing T2*-weighted axial image shows the normal insertion of the collateral ligament (cl) into the lateral aspect of the volar plate (vp). The torn and retracted accessory component of the ulnar collateral ligament (large arrow) is not seen in continuity with the periphery of the volar plate. The volar plate represents a normal capsular thickening forming the floor of the metacarpophalangeal joint. Also shown are the common extensor tendon (et) and sagittal bands (small arrows). The sagittal bands of the extensor hood extend from the common extensor tendon to the volar plate and course in the plane between the interosseous tendon (it) and collateral ligament (ct). (C) Normal anatomy of the third metacarpal at the level of the metacarpophalangeal joint. Axial color graphic.

FIGURE 10.245 ● (A) Thumb capsular ligaments of the metacarpophalangeal and interphalangeal joints. Lateral color graphic. (B) Sagittal FS PD FSE image with a torn checkrein ligament. The accessory collateral ligament was also injured in this patient, who sustained a thumb dislocation.

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An ulnar collateral ligament tear, sometimes called ulnar collateral ligament rupture, gamekeeper's thumb, or skier's thumb, involves disruption of the ulnar collateral ligament of the first metacarpophalangeal joint (Fig. 10.246) and is frequently associated with a proximal phalanx base fracture.¹⁶⁹^,¹⁷⁰ The capsule of the metacarpophalangeal joint of the thumb is reinforced by the volar plate, the collateral ligaments, and the extensor pollicis brevis tendon. The adductor aponeurosis is the adductor pollicis aponeurosis. The size of the tear varies, depending on the degree of ulnar collateral ligament retraction deep to or superficial to (Stener's lesion) the adductor aponeurosis. Ulnar collateral ligament injuries of the thumb metacarpophalangeal joint are relatively common. The majority of ulnar collateral ligament ruptures occur distally. Stener's lesion, which accounts for 50% to 70% of complete tears, is frequently found in skiers (80% of cases). Ulnar collateral ligament injuries are most frequently seen in young to middle-aged males, especially those who participate in high-risk activities such as football, hockey, wrestling, basketball, and skiing.

Etiology, Pathology, and Clinical Features

The mechanism of injury is usually forceful abduction of the thumb, which applies hyperextension stress to the ulnar collateral ligament. Ulnar collateral ligament tears may result from a fall with hyperextension and abduction, as occurs in skier's thumb, or from chronic injury to the ulnar collateral ligament, as occurs in gamekeeper's thumb.

The ulnar collateral ligament may sustain a partial tear, usually at its distal attachment to the proximal phalanx, or a complete tear, more frequently affecting the distal portion (see Fig. 10.246) than the midsubstance of the tendon. Complete ulnar collateral ligament tears result in metacarpophalangeal joint instability, with at least 20° greater laxity than the contralateral thumb. Displacement of the ulnar collateral ligament proximal and superficial to the adductor pollicis aponeurosis is called the Stener's lesion.¹⁶⁹^,¹⁷⁰ Additional pathologic changes include an avulsed bone fragment (not required for Stener's lesion) and volar subluxation of the proximal phalanx. In nondisplaced ulnar collateral ligament tears there is discontinuity without retraction and an intact adductor aponeurosis covering the distal ulnar collateral ligament. Displaced tears are Stener's lesions with proximal retraction (ligament folding) proximal to the metacarpophalangeal joint. In Stener's lesion the proximal margin of the adductor aponeurosis intersects or abuts the folded ulnar collateral ligament and the distal end of the ulnar collateral ligament is turned 180° and directed proximally.

Metacarpophalangeal joint pain is a common clinical sign. Pain is greatest on the ulnar side and may radiate from the metacarpal head to the proximal phalanx. Additional clinical findings include:

Swelling
Reduced pinch strength
A mass caused by the displaced ulnar collateral ligament stump on the ulnar side of the metacarpophalangeal joint or proximal to the metacarpophalangeal joint
Abnormal thumb rotation (rotation of the proximal phalanx on the intact axis of the radial collateral ligament)
Absent endpoint on joint stress test in complete tears
Instability in metacarpophalangeal flexion in proper collateral ligament tears with intact accessory collateral ligament and volar plate
Instability in flexion and extension in complete ulnar complex disruption
Stability less than or equal to 10° of joint space opening
Instability greater than or equal to a 30° abduction arc on stress relative to the contralateral side

FIGURE 10.246 ● Gamekeeper's thumb with rupture of the distal attachment (curved arrow) of the ulnar collateral ligament (u). The torn ulnar collateral ligament remains deep to the overlying adductor aponeurosis (small arrows). In Stener's lesion (not present in this case), the torn ulnar collateral ligament relocates superficial to the adductor pollicis aponeurosis after the abduction injury occurs. (A) T1-weighted coronal image. (B) STIR coronal image.

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Classification

Ulnar collateral ligament injuries are classified as either partial tears (grades I and II) or complete ruptures (grade III):

Grade I: Stretching of the ligament
Grade II: Incomplete but discrete tears
Grade III: Complete ruptures with or without Stener's lesion

MR Appearance

T1-weighted, FS PD FSE, or T2*-weighted coronal MR images demonstrate edema, thickening, disruption, displacement, or entrapment of the ulnar collateral ligament.¹⁴⁷ The thumb should be positioned so that the radial collateral ligament is included in the imaging plane. With MR imaging, it is possible to differentiate between ulnar collateral ligament displacement and nondisplaced tears. Spaeth et al.¹⁶⁹ reported that MR imaging was 67% specific for identifying all tears. However, it was 100% sensitive and 94% specific for demonstrating ulnar collateral ligament displacement in gamekeeper's thumb. Sonography has also been used in the differentiation of displaced and nondisplaced tears of the ulnar collateral ligament,¹⁷¹ although MR imaging has documented better results.¹⁷²

The key diagnostic sign is discontinuity of the ulnar collateral ligament attachment to the proximal phalanx. However, specific MR findings depend on the type of lesion.

In incomplete or complete rupture without Stener's lesion, findings include the following:

Ulnar collateral ligament remains deep to the overlying adductor aponeurosis.
Ulnar collateral ligament thickening
Discontinuity at the ulnar collateral ligament attachment to the proximal aspect of the proximal phalanx (thumb)
Edema and fluid superficial and deep to the ulnar collateral ligament
Subchondral edema with or without osseous avulsion at the ulnar collateral ligament distal attachment to the proximal phalanx
Soft-tissue edema superficial to the adductor aponeurosis
Ulnar displacement of the ulnar collateral ligament and adductor aponeurosis
Ulnar collateral ligament orientation along the long axis of the first ray (thumb)
Thickened ulnar collateral ligament with central signal inhomogeneity (focal areas of edema)
Fluid interposed between the base of the proximal phalanx and the retracted ligament
Fluid plane between the distal ulnar aspect of the first metacarpal and the ulnar collateral ligament and between the ulnar collateral ligament and the adductor aponeurosis

In complete ulnar collateral ligament rupture with Stener's lesion (Fig. 10.247), findings are:

Retracted mass of ulnar collateral ligament

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Ulnar collateral ligament trapped either completely superficial to or intersecting the overlying adductor aponeurosis
Gross displacement of the ulnar collateral ligament medial to the adductor aponeurosis
Ulnar collateral ligament directional vector with increased horizontal orientation (no longer parallel to long axis of first digit) (see Fig. 10.247)
Displacement of the retracted ulnar collateral ligament varies from 90° to as much as 180° of pronation (Fig. 10.248).
“Yo-yo on a string” appearance of Stener's lesion caused by a retracted and balled-up ulnar collateral ligament (the yo-yo) with the more proximal linear adductor aponeurosis (the string)

FIGURE 10.247 ● (A) Progression of a displaced ulnar collateral ligament (UCL) forming Stener's lesion with the proximal margin of the abductor aponeurosis intersecting and entrapping the folded UCL. (B) Stener's lesion with the thickened mass-like morphology of the retracted UCL oriented in a horizontal direction. The UCL is perpendicular to the long axis of the thumb and to the course of the adductor aponeurosis.

FIGURE 10.248 ● Stener's lesion with complete 180° rotation of the torn ulnar collateral ligament (UCL). The flipped UCL is visualized proximal to the metacarpophalangeal joint on the axial image. (A) Coronal FS PD FSE image. (B) Axial FS PD FSE image.

Treatment

Partial tears (grades I and II) and complete tears without Stener's lesion may heal with conservative treatment (a thumb spica cast or a custom splint). Fibrosis and granulation tissue in complete tears may delay or preclude ligament reattachment, however. Since the adductor pollicis aponeurosis may be interposed between the disrupted portions of the ulnar collateral ligament, surgical repair is often indicated, particularly for complete rupture with Stener's lesion and for volar subluxation of the proximal phalanx. Surgical procedures include primary repair of the torn ulnar collateral ligament (for acute and subacute injuries) and reconstruction of chronic complete ulnar collateral ligament ruptures. Complications include injury to the superficial branch of the radial nerve and failure of ulnar collateral ligament repair, leading to loss of joint motion.

FIGURE 10.249 ● Normal anatomy of the ligaments reinforcing the digital tendon sheath. A1 through A5 represent the annular ligaments and C1 through C3 represent the cruciform ligaments. The longest annular ligament, the A2 pulley, is located on the proximal diaphysis of the proximal phalanx. Sagittal color graphic.

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Tendon Injuries

MR imaging has been used to identify the anatomy, site, and specific flexor tendon involved in primary tendon tears¹⁷³ or postsurgical retears. The differential diagnosis of tendon injury includes motor nerve injuries (which impair active motion but in which the viscoelastic muscle tendon unit remains intact), extensor tendon injuries, flexor extensor tenosynovitis, and rupture. These conditions are often difficult to diagnose on clinical examination, and MR studies can be used to evaluate and detect subluxation, synovitis, or tears. Chronic tenosynovitis may lead to tendon attrition and result in tear. MR studies used for follow-up after flexor tendon repair identify specific complications, such as peritendinous adhesions, frank rupture, and rupture with callus. A frank rupture is associated with a larger tendon gap. An elongated callus is characterized by a thin fibrous continuity across the rupture site.¹⁷⁴

Extensor hood injuries may also be detected on MR images, which display the components of the extensor hood, including the sagittal bands.¹⁷⁵

Flexor Annular Pulley Tears

Flexor annular pulley tears represent lesions of the fibro-osseous theca or flexor tendon sheath. The fibrous portion of the fibro-osseous flexor tunnel is composed of the five digital annular pulleys (A1 to A5) (Fig. 10.249), which are condensations of the transversely oriented fibrous bands and the cruciate pulleys (C1 to C3). Functionally, the A2, at the proximal aspect of the proximal phalanx, and the A4, at the mid-aspect of the middle phalanx, are the most important of the digital annular pulleys.¹⁷⁶ The digital annular pulleys function to stabilize the flexor tendons during flexion and resist ulnar/radial displacement as well as palmar bowing.

Flexor annular pulley tears, which represent 30% of finger injuries, may affect the long (baseball) and ring fingers, the A4 pulley (annular), the interval between the A2 and the A4 pulleys, the A5 pulley, or the first two cruciate pulleys. Injuries range from attenuation to frank disruption, and with severe injury there is overt bowstringing. They are most often seen in young adults, especially professional baseball pitchers (usually from 20 to 30 years of age) and rock climbers (20 to 40 years of age). They occur more often in males, probably related to participation in activities that cause forcible contraction of the flexor digitorum profundus. Almost 50% of pulley tears occur in elite climbers. The ring and middle fingers are usually affected in climbing injury, and the middle finger is most often injured in baseball pitchers.

Etiology, Pathology, and Clinical Features

As mentioned, the primary mechanism is forcible contraction of the flexor digitorum profundus against extreme force. Injuries in professional baseball pitchers are related to use of the distal tip of the long finger for control with increased angular velocity in the throwing mechanism. Rock climbing injury (Fig. 10.250) is related to support of the body weight with the distal interphalangeal joint in flexion. These injuries are caused by high stress and repetitive microtrauma. Local trauma varies with grip techniques (loads up to 700N). With the crimped technique the metacarpophalangeal joint is in extension, the proximal interphalangeal in flexion, and the distal interphalangeal in extension, producing excessive forces on the A2 and A3 digital annular pulleys.

Pathologically there may be bowstringing of flexor tendons¹⁷³ with failure of the A4 pulley, disruption of the interval between the A2 and A4 pulleys, and involvement of the A5 pulley and the first two cruciate pulleys. Less commonly there is combined injury of the A2 and A4 pulleys. With partial tears there is no tendon bowstringing. Volar subluxation of the tendon indicates a digital annular pulley tear, and there may be associated tenosynovitis and fibrous tissue. Differentiation between A2 and A3 pulley injuries (proximal phalanx) and A2 pulley ruptures requires forced flexion.

Patients present with pain and tenderness over palmar (volar) and lateral aspects of the flexor tendon. The increased tenderness is associated with inflammation. There is a feeling of tendon fullness, caused by fluid or hemorrhage, and flexion of the distal interphalangeal may cause discomfort. Weakness is also a common finding, and baseball players find a decreased velocity of pitches. Additional findings include tendon bowstringing, soft-tissue swelling, and a restricted range of motion.

MR Appearance

The diagnosis is indicated by attenuation or rupture of the flexor tendon sheath pulley on axial images. Additional findings include:

Bowstringing from the proximal interphalangeal joint to the base of the proximal phalanx on sagittal images in complete rupture of the A2 pulley
Bowstringing from the proximal interphalangeal but not reaching the base of the proximal phalanx in incomplete rupture of A2 pulley
Bowstringing at the level of the proximal phalanx to a region distal to the proximal interphalangeal joint in rupture of both the A2 and A3 pulleys
Bowstringing at the level of the middle phalanx in A4 rupture
Fluid signal associated with the affected pulley

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Tendon sheath cysts
Fibrous tissue
Tendon displacement
- Anterior displacement relative to the proximal aspect of the proximal phalanx in the A2 pulley area
- Anterior displacement relative to the middle phalanx in the A4 pulley area
- Medial or lateral subluxation
Fibrous scar tissue
Proximal or distal interphalangeal joint fluid
Tenosynovitis

FIGURE 10.250 ● (A) Bowstringing of flexor tendons secondary to rupture of the A1 and A2 pulleys. Bowstringing of the flexor tendons is associated with rock-climbing pulley injuries. Ruptures may occur at the A3, A2, A4, or A1 pulleys. Sagittal color graphic. (B) T1-weighted sagittal image with bowstringing of the flexor tendons at the level of the A2, A3, and A4 pulleys in a rock climber. Ruptures occur frequently in the A3, A2, and A4 pulleys. The pulleys of the middle or long finger are stronger than the pulleys in the index, ring, and little fingers. FDS, flexor digitorum superficialis; FDP, flexor digitorum profundus. (C) Rupture of the A2 pulley of the third finger. There is volar displacement of the flexor tendons, with the torn A2 pulley identified between the proximal phalanx and the flexor tendons.

Treatment

Delayed diagnosis results in fixed contractures of the proximal interphalangeal joint with fibrosis and scar tissue and weakness. Tenosynovitis or partial digital annular pulley tears without bowstringing may be treated conservatively with immobilization, anti-inflammatory medication, and steroid injections if there is a strong inflammatory component (steroids may alter the healing process, however). Complete rupture of the flexor pulley system requires surgical reconstruction.

Flexor Digitorum Profundus Avulsions

Flexor digitorum profundus avulsion (Fig. 10.251), also referred to as jersey finger, is a distal avulsion of the flexor digitorum profundus tendon from its insertion on the distal phalanx. The relevant anatomy is that of the flexor tendon sheath pulley system, which consists of the following structures:

A2 and A4 pulleys, critical for maximal finger flexion, which originate from bone
Five annular pulleys (A1 to A5), which are thick and well defined
Three cruciate pulleys (C1 to C3), which are thin and collapse in flexion
Palmar aponeurosis
Short and long vincula, a dorsal mesotenon that carries blood supply

Avulsions most frequently involve the ring finger (75% of cases) and usually occur in young male athletes. The tendon may be retracted to the palm, the proximal interphalangeal joint, or the A4 annular pulley (osseous avulsions are caught at the level of the A4 pulley). The distal interphalangeal joint is in full extension after flexor digitorum profundus avulsion and the retracted flexor digitorum profundus is thickened.

Etiology, Pathology, and Clinical Features

The usual mechanism of injury is traumatic disruption, and it is often seen when an athlete grasps the jersey of another player, as might occur in soccer or football players (especially tight ends and defensive players). In basketball it often results from catching a finger on the rim of the basket during a slam dunk. Disruption occurs when there is forced extension of the flexed distal interphalangeal. The long, middle, and ring fingers share a common muscle belly and the flexor digitorum profundus insertion has a low threshold for disruption. The ring finger is at highest risk because during gripping it is more prominent than the long finger and is tethered by bipennate lumbrical muscles.

Pathologically there are three types of flexor digitorum profundus avulsion injuries:

Type I: Tendon retraction into the palm, blood supply disruption, and a tendon sheath scar
Type II: Tendon retracts to the proximal interphalangeal joint and the flexor digitorum profundus is caught at the chiasm of the flexor digitorum superficialis.
Type III: Flexor digitorum profundus avulsion plus a large osseous fragment. The bony fragment is lodged at the distal edge of the A4 pulley.

Histologically collagen fibers (type I in tendons) are seen parallel to the long axis. The endotenon binds collagen, the epitenon is similar to synovium, and the paratenon surrounds the epitenon and contains elastic fibers and the tenosynovium of the wrist flexors. In tears, there is collagen failure or disruption. Elastin is found in small amounts in tendons, and ground substance (proteoglycans, glycosaminoglycans, plasma proteins) provides the viscoelastic properties of tendons.

Clinically patients present with tenderness along the flexor digitorum profundus and inability to flex the distal interphalangeal joint. Local tenderness is greatest at the flexor digitorum profundus stump site (the proximal interphalangeal level at the A4 pulley or the distal palm). Associated swelling and ecchymosis are usually seen.

Classification

Tendon disruptions are classified according to five zones:

Zone 1: from the fingertip to the midportion of middle phalanx
Zone 2: from the midportion of the middle phalanx to the distal palmar crease
Zone 3: from the distal palmar crease to the distal edge of the carpal tunnel
Zone 4: in the carpal tunnel
Zone 5: proximal to the carpal tunnel

Flexor digitorum profundus disruptions (avulsion injuries) are classified into four types:

Type I: Flexor digitorum profundus retracts to the palm.
Type II: Vincula vessels are intact and there is a tether retracting the flexor digitorum profundus.

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Type III: A large fragment of bone catches on the A4 or A5 pulley.
Type IV: Fractures at the flexor digitorum profundus insertion; retraction is permitted by separation of tendon from bone.

FIGURE 10.251 ● (A) A sagittal section of a finger shows the capsules and the relations of the joints. (B) Complete rupture of the flexor digitorum profundus of the ring finger (fourth digit) at the level of the mid-aspect of the proximal phalanx. Sagittal FS PD FSE image. (C) A transverse section through the index finger at the level of the proximal phalanx. (D) Axial FS PD FSE image of a flexor digitorum profundus (FDP) tear with rupture at the mid-aspect of the proximal phalanx of the ring finger. The ring finger is most frequently involved in FDP avulsions. In a type II avulsion, the FDP is caught at the chiasm of the flexor digitorum superficialis.

MR Appearance

The most obvious sign of flexor digitorum profundus avulsion is an absent or retracted tendon on axial or sagittal MR images. T1- or PD-weighted images provide soft-tissue detail, but gradient-echo techniques provide excellent tendon visualization. Key findings include:

Discontinuity indicates complete disruption.
Tendon retraction, most easily visualized on sagittal images
Marrow edema at the site of the avulsion fracture
Profundus tendon in the area between the divisions of the flexor digitorum superficialis tendon
Fluid signal intensity along the course of the retracted flexor digitorum profundus
Associated tendinosis and tenosynovitis
Partial tendon tear
Fluid surrounding the flexor digitorum superficialis slips (divisions) and centrally (within the flexor digitorum profundus tendon gap) on axial images
Normal tendons demonstrate homogeneous hypointensity on both T1-weighted and FS PD FSE images.

Treatment

Untreated avulsions lead to deformity and loss of function, and a delay in treatment leads to inflammation and tendon degradation, making operative repair difficult. Primary surgical repair of the tendon is usually required, with reinsertion into the base of the distal phalanx. Reconstruction may also be needed.

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