Treatment of Acute SL (Scapholunate) Dissociation

September 8th, 2008

An acute complete tear of the ligament between the scaphoid and lunate bones commonly results from a forceful hyperextension injury to the wrist---for example after a fall onto an outstretched hand or a car accident. Such a complete tear allows the scaphoid bone to flex and the lunate to extend---a type of carpal instability referred to as a DISI deformity. The connection between these 2 bones needs to be reestablished, otherwise pain will persist and arthritis will develop. Simple cast treatment is not an option. Such an injury usually is accompanied by swelling and pain-----and this means you should get an xray rather than making the assumption that it is merely a sprain.

When an xray looks normal, but dorsal pain exists----a partial tear of the ligament may be present, but so long as carpal instability is absent, conservative treatment in a cast or splint may allow recovery. If, after a few months the pain persists, diagnostic wrist arthroscopy allows evaluation and debridement. Yes--an MRI scan may be indicated, but false negative studies usually mean that even in the presence of a normal study, there still might be a treatable cause of the pain at the time of arthroscopic intervention.

The results of surgery to repair the SL ligament are more favorable when performed within 6-12 weeks after injury, seemingly related to improved DNA synthesis and collagen repair. In fact, after 3 months when these injuries are considered chronic, results deteriorate, and more of a salvage procedure may be indicated.
The literature is clear that the most optimal acute treatment is an open repair of the ligament combined with a capsular back-up (capsulodesis) and the placement of temporary pins for 8 weeks. There still remains a risk of more surgery if the ligament does not heal or if carpal instability persists.

What is confusing, potentially, is the numerous alternatives described in the literature----many of which are recommended after 3 months. These include tendon transfers to rebuild the ligament and the RASL procedure, where a screw is placed between the scaphoid and lunate. Care should be taken to understand the pros and cons of these as compared to more time-honored salvage procedures such as limited wrist fusion and proximal row carpectomy.

Related Photos:

An acute SL dissociation is shown--a gap greater than 3 mm between the scaphoid and lunate (see arrow)

Acute SL dissociation results in a near vertical scaphoid--thus the normal angle increases to greater than 60 degrees