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Scapholunate Dissociation: FOOSH, no fracture but still not better

What is scapholunate dissociation?

The scapholunate interosseous ligament (SLIL) is a C-shaped structure which connects the scaphoid and the lunate and is important for carpal stability. Most injuries are degenerative in nature, occurring in patients over 80 years of age with arthritis but acute injuries are associated with FOOSH style injuries.

What are the clinical features to make me concerned for acute scapholunate dissociation?

A patient presenting with dorsal and radial-sided wrist pain with after a FOOSH, specifically with the wrist in extension and ulnar deviation. Typically, pain will be increased with pressure applied to the carpal bones (ex. push up position), clicking or catching of the wrist, “giving way” with lifting or grasping, and instability or weakness. Tenderness may occur just distal to Lister’s tubercle or in the snuffbox. There may also be swelling on the dorsum of the wrist, pain (worse with extension and radial deviation) and a positive Watson’s test. Watson’s test is performed by grasping the patient’s thumb with the 1st and 2nd digits over the scaphoid. The scaphoid is dorsally subluxed by bringing the thumb in a volar and opposed direction. A positive test is dorsal wrist pain or a clunk which indicates scapholunate instability.

Investigations:

AP and lateral views of the wrist are a start but the clenched fist view is the best radiograph. A gap between the scaphoid and the lunate greater than 3mm is called the Terry Thomas sign and is positive for SL dissociation. MRI can be considered but is considered to have a low sensitivity. Arthroscopy is the gold standard.

Management:

Non-operative management is appropriate for acute and undisplaced SLIL injuries. Requires casting or approximately 8weeks with periodic imaging and follow up. Operative management is required for any form of malaligment, failure to improve after 18 months, SL dissociation due to scaphoid fracture, presence of associated arthritis or other complicating factors. This can be achieved in multiple ways such as K-wire fixation, direct repair of the ligament or tendinous grafting, depending on injury.

Complications:

A failure to adequately identify and appropriately managed SLIL injuries can lead to scaphoid lunate advance collapse (SLAC) which causes progressive degeneration of the radiocarpal and midcarpal joints and has a significant effect on function in the hand and wrist.

Recap:

FOOSH without obvious fracture; consider ligamentous injury, especially SLIL injury. Normal xrays will not adequately assess, always order clenched fist view. Most cases treated with casting but some will require surgical management. Lack of management can lead to progressive degeneration of the wrist and serious functional impairment.

Anthony Caragianis, PGY3 SEM, University of Ottawa

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