Magnetic Resonance Imaging

Fluid signal in the rotator cuff tendon indicates a tear; partial is distinguished from full-thickness by depth of fluid signal.

Fatty atrophy of rotator cuff muscles is seen as increased signal on T1-weighted images.

Biceps tendon subluxation or dislocation
is well visualized on axial views; tendon splits or complete tears are
detected in 3 planes (axial, coronal, sagittal).

Glenoid labral tears are identified by
abnormal morphology and fluid dissecting deep to or within the labrum;
paralabral cysts may be located in the suprascapular or spinoglenoid
notch.

Acromial shape (flat, curved, hooked) and subacromial spurs are detected on sagittal oblique views.

Collateral ligament tears are detected by fluid or contrast through the ligament, best seen on coronal oblique views (Fig. 1).

Medial and lateral epicondylitis present
as flexor or extensor tendinosis (increased T2 signal), partial tear
(fluid signal partly dissecting through the tendon), or complete tear
(complete disruption of tendon with only fluid at origin); may be
accompanied by bone marrow edema at epicondyles.

Biceps tendon pathology is best seen on axial views at the insertion on radial tuberosity.

Triceps tendon pathology is best seen on sagittal and axial views at the insertion on the olecranon.

Bone marrow edema secondary to arthritis or fracture is detected on fluid-sensitive sequences.

Intra-articular bodies may have variable signals.

TFCC normally is dark on all sequences:
Degeneration, perforations, and tears are defined by abnormal signal
within the fibrocartilage; tears are associated with distal radioulnar
joint effusion.

Intrinsic ligament (scapholunate and
lunotriquetral ligaments) tears are detected by fluid or contrast
passage through the ligament.

All abnormalities and extrinsic ligaments may be better shown by MRA.

Carpal tunnel is assessed on axial views for median nerve enlargement or signal abnormality and flexor tendon pathology.

Ulnar nerve and Guyon canal are assessed on axial views for possible mass or ulnar artery aneurysm.

Articular cartilage defects may be detected directly or indirectly (the latter through associated bone marrow changes).

Kienböck disease typically is accompanied by diffuse decreased signal in the lunate.

Hook of hamate fractures: Axial views are best.

Fractures can be identified by linear signal abnormality and surrounding bone marrow edema.

Acetabular labrum morphology/tears are better identified by direct than indirect MRA.

Gluteus and hamstring tendons normally are dark on all sequences, but when torn, the MRI shows fluid signal.

The most sensitive sequence for meniscal
tears is the intermediate-weighted sequence, which shows tears as
increased signal reaching the meniscal surface.

Flipped fragments may be detected as a double PCL sign (sagittal view) or occasionally seen in the medial gutter (coronal view).

Postoperative meniscal evaluation may be aided by MRA.

Complete ACL tears are detected by frank
disruption with abnormal signal, failure to parallel Blumensaat line,
and secondary signs (anterior tibial translation, specific contusion
pattern).

Collateral ligament sprains may be grade
1 (abnormal signal adjacent to ligament), grade 2 (fluid signal within
and adjacent to ligament), or grade 3 (complete disruption of ligament)
(3).

Patellar tendinosis manifests with abnormal thickness and signal, and tendon tears are accompanied by fluid signal.

Quadriceps tendon tears should be assessed in all 3 planes (sagittal, coronal, and axial) for width of involvement.

Articular cartilage defects may be
detected in several ways: T1-weighted 3D gradient echo sequences, as
decreased signal; fluid-sensitive sequences, as fluid at the defect
site, often accompanied by underlying bone marrow abnormalities;
contrast-enhanced T1 sequences, as contrast at site of defect

The Achilles tendon normally is dark on
all sequences: Degeneration may be detected by abnormal thickness and
internal signal; tears are seen as fluid signal.

PTT pathology is seen as abnormal tendon
thickness or abnormal signal within the tendon; associated findings are
PTT dysfunction (heel valgus deformity, midfoot fault, and os
naviculare).

Peroneal tendon subluxation is detected
by axial views: Presplit condition (boomerang deformity) or actual
split of the peroneus brevis tendon is detectable in 3 planes; complex
fluid in peroneal sheath suggests tenosynovitis.

Lateral ankle ligament (talofibular and
tibiofibular) injuries are classified as grade 1 (increased signal),
grade 2 (partial tear with fluid signal), or grade 3 (complete
disruption) (4).

Sinus tarsi normally contains fat and is
best evaluated on a sagittal T1-weighted image for loss of fat signal
in sinus tarsi syndrome.

Plantar fasciitis accompanied by
increased signal and abnormal thickness of the plantar fascia may have
associated reactive bone marrow edema in the calcaneus.

A tumor appears as a marrow replacement process on T1-weighted images (5).

T2-weighted images are useful for defining extension into adjacent soft tissues.

Contrast-enhancement is useful for differentiating posttreatment residual or recurrent disease from fibrosis.

Fluid levels may be identified in bone
cysts, giant cell tumors, chondroblastomas, telangiectatic
osteosarcoma, and any lesion with a fracture (Fig. 2).

Only a small percentage of tumors (including lipomas, cysts, and vascular malformations) can be characterized definitively.

Some lesions (e.g., nerve sheath tumors,
giant cell tumor of a tendon sheath, some fibrous tumors such as
elastofibroma and desmoid tumors) have a few specific MRI
characteristics.

Contrast enhancement characteristics may
help distinguish benign and malignant soft-tissue lesions, but much
overlap occurs in enhancement (6).