Scapholunate Dissociation

By admin Last updated Oct 30, 2023

Ovid: 5-Minute Sports Medicine Consult, The

Keith A. Anderson

Robert L. Jones

Basics

Description

Complete tear of the scapholunate interosseous ligament (SLIL) with an additional tear of 1 or more secondary ligament restraints

Epidemiology

Most common ligamentous instability in the wrist
More precise epidemiologic data are lacking.

Risk Factors

Active individuals who have ulnar-negative variance; shorter distal ulna compared with the radius on a neutral anteroposterior (AP) radiograph of the wrist (1)

Etiology

Often a fall on an outstretched hand, with hyperextension and ulnar deviation
Axial compression can force the capitate between the scaphoid and lunate.
May result from minor repetitive trauma (2)
Repetitive motion after an isolated SLIL injury may produce attritional changes in the secondary stabilizers, leading to their eventual failure, thus completing the scapholunate dissociation (3).

Diagnosis

Early diagnosis offers the best chance for successful surgical outcome.
There are different levels of instability, which can be classified by increasing severity of wrist instability (4):
- Occult instability: Isolated tear or attenuation of a portion of the SLIL. There is no radiologic evidence, and wrist pain is with mechanical loading.
- Dynamic scaphoid instability: Subtotal or complete tear of the SLIL, including the dorsal portion, with a partial extrinsic ligament injury. May have normal static radiographs, but instability will be apparent on stress radiographs.
- Scapholunate dissociation: Involves a complete tear of the SLIL with additional tear of 1 or more secondary ligaments. The scaphoid usually rotates into flexion, and the lunate rotates into extension. This is apparent on plain static radiographs.
- Dorsal intercalated segment instability (DISI): Term used to describe the shifted positions of the bones of the carpus due to lack of association between the lunate and scaphoid. Abnormalities include flexion of the scaphoid, extension of the lunate and triquetrum, and dorsal and proximal translation of the capitate and distal carpal row. Apparent on lateral static radiograph.
- Scapholunate advanced collapse (SLAC): End stage of the spectrum of instability. There is predictable and progressive degeneration and arthritis of the carpus due to the irreversible postural changes of the scaphoid, capitate, and lunate.

History

Need to establish the timing of the injury (2):
- Acute <4 wks
- Subacute 4 wks to 6 mos
- Chronic >6 mos
Patient may report a fall or sudden load applied to the wrist, but may not recall any specific fall or injury.
May report pain or weakness with hyperextension loading of the wrist
Often will not seek immediate care because initial injury seems too trivial (3)
Subacutely, there may be symptoms of painful popping or clicking with activities, or decreased grip strength
Later on, limited motion may be a complaint (1,4).

Physical Exam

In the acute setting, pain may be poorly localized about the periscaphoid area and preclude most provocative wrist ligament testing. Swelling may be diffuse or localized to the scapholunate region (4)[C].
In the subacute setting, there is usually well-localized tenderness about the scaphoid and dorsal scapholunate interval distal to Lister's tubercle.
The patient may have weakness of grip and pinch strength (2).
Watson scaphoid shift test should be performed:
- Patient places wrist in ulnar deviation, and the physician puts dorsal pressure on the scaphoid tubercle with the thumb. The physician then radially deviates the patient's wrist. Relief of thumb pressure will allow the scaphoid to reduce, often with an audible or palpable clunk. Pain with a clunk may represent scapholunate instability.

Diagnostic Tests & Interpretation

Imaging

Imaging should be obtained in individuals with appropriate history and positive scaphoid shift test.
Radiographs of the opposite wrist should always be obtained (2,5)[C].
Initial views should include AP, lateral
Initial radiographs may appear normal, so stress radiographs should be obtained when carpal instability is suspected but static radiographs are normal.
Normal static and stress films in the acute situation do not always rule out serious injury (4)[C].
Key findings on the lateral film (wrist in neutral):
- Scapholunate angle >70° is considered highly suggestive of diagnosis (normal 30–60°) (2,3,4)[C]
- Radiolunate angle exceeding 15° indicates DISI (3,4)[C].
Key findings on the AP film:
- Increased scapholunate joint space (>2 mm, increased compared to contralateral), referred to as scapholunate diastasis or the “Terry Thomas sign” (3)[C]
- Scaphoid ring sign: Distal scaphoid tubercle is superimposed on the scaphoid waist when scaphoid is flexed more than 70°
AP grip (clenched fist) view is the most frequent stress view. It profiles the scapholunate joint and demonstrates pathologic scapholunate widening (>2 mm) under axial loaded conditions (4)[C]. Additional stress view could include AP in ulnar deviation (2).
CT arthrography has been reported as having a 95% sensitivity and 86% specificity for detecting SLIL tears when compared with arthroscopy (4)[B].
MRI with average of 71% sensitivity and 88% specificity in detecting scapholunate tears, but high variability between individuals. Many authors conclude that MRI is not reliable for diagnosing SLIL injury (1,3,4)[B].
Arthrography and MRI are anatomic and not functional evaluations.
Simple fluoroscopy is a helpful functional ancillary study (2,4)[C].
Wrist arthroscopy is the gold standard for diagnosis.

P.519

Differential Diagnosis

Differential diagnosis (2,3):

Scaphoid or other carpal fracture
Radial styloid or distal radius fracture
Synovitis
Radioscaphoid impingement
Occult ganglion
Lunotriquetral instability
Triangular fibrocartilage complex tear
Osteoarthritis or rheumatoid arthritis
Kienböck's disease

Treatment

Treatment must be predicated by the patient's symptoms and clinical exam, not imaging.
The treatment is most often surgical, so do not delay referral.
Proper treatment may be challenging due to delay in recognition (3).

ED Treatment

Stabilize with a thumb spica splint (5).

Medication

NSAIDs or Tylenol for pain

Additional Treatment

There has been some success with casting, splinting, NSAIDs, and therapy without surgical intervention for dynamic instability (4)[C]. This would include a short arm cast for 2–6 wks, followed by removable splint for active range of motion (ROM) exercises and gentle strengthening across the wrist (2)[C].
For acutely injured scapholunate joint, some will use closed reduction and K-wire fixation.
There has also been some success with external reduction of the scaphoid followed by immobilization of the wrist in plaster, but most consider this unreliable for reduction (3)[C].

Surgery/Other Procedures

In general, in wrists without fixed bony deformity, attempts should be made to restore the bony relationships with soft tissue augmentation; in wrists with fixed deformity, salvage procedures are needed to alleviate pain (3).
There are many opinions as to the specifics of surgical intervention, but in general, the procedures performed are dictated based on the severity classification of the wrist instability:
- Occult instability:
  - There has been some success with arthroscopic debridement with or without pinning, but usually this is treated with conservative measures (4). There is also some new evidence for electrocautery for electrothermal collagen shrinkage following arthroscopic debridement (3)[C].
- Dynamic instability and scapholunate dissociation with a repairable SLIL:
  - Treatment of choice is open reduction with scapholunate repair and a dorsal capsulodesis. Delayed repair is somewhat controversial, but there has been reported success 8 wks after injury if the SLIL is adequate for repair (1,4)[C].
- Scapholunate dissociation without repairable SLIL:
  - In subacute or chronic injuries, the goal is to reestablish the critical scapholunate linkage.
- DISI:
  - A salvage procedure is performed to restore alignment, improve load distribution, and attempt to slow degenerative changes.
- SLAC:
  - Salvage procedures appear to be the only option, such as excision of scaphoid, capitate-lunate-hamate-triquetral arthrodesis, or carpectomy (4)[C].

Ongoing Care

Follow-Up Recommendations

Following repair, immobilize wrist for 8 wks then slow rehabilitation program
No return to competitive sports for 4–6 mos postoperatively (1)[C]
Avoid power gripping and weight-bearing exercises of the upper extremity.
Gentle putty or sponge gripping can help improve grasp.
Physical therapy should be performed within pain tolerance (2).
Decisions about return to play must be individualized based on sport-specific demands.
In general, an athlete may return after demonstrating progression in strength and ROM in a supervised rehabilitation program.

Complications

Arthritis of the wrist, which can be chronic and debilitating
Inherent complications of surgery

References

1. Cohen MS. Ligamentous injuries of the wrist in the athlete. Clin Sports Med. 1998;17:533–552.

2. Lewis DM, Osterman AL. Scapholunate instability in athletes. Clin Sports Med. 2001;20:131–140, ix.

3. Manuel J, Moran SL. The diagnosis and treatment of scapholunate instability. Orthop Clin North Am. 2007;38:261–277.

4. Kuo CE, Wolfe SW. Scapholunate instability: current concepts in diagnosis and management. J Hand Surg [Am]. 2008;33:998–1013.

5. Daniels JM, Zook EG, Lynch JM. Hand and wrist injuries: Part I. Nonemergent evaluation. Am Fam Physician. 2004;69:1941–1948.

Codes

ICD9

842.09 Other wrist sprain