The scapholunate ligament is the most important intercarpal ligament, synchronising the movement of the scaphoid and lunate to maintain the normal carpal alignment. Its rupture allows the scaphoid to palmarly flex and rotate while the lunate extends (DISI pattern), producing the progressive carpal collapse that if untreated leads to scapholunate advanced collapse (SLAC) arthritis — the most common pattern of wrist arthritis.
| Origin | Scaphoid proximal pole |
|---|---|
| Insertion | Lunate medial surface |
| Actions | Synchronises scaphoid and lunate motion during wrist movement, maintaining carpal alignment |
|---|
The Watson scaphoid shift test provokes pain and a clunk when the scaphoid subluxes dorsally during the test, indicating SL instability. Radiographic diastasis exceeding 3 mm between the scaphoid and lunate on a clenched fist AP view (Terry Thomas sign) confirms complete ligament rupture. Acute complete tears are repaired primarily; chronic instability requires ligament reconstruction with the flexor carpi radialis tendon.
Complete SL ligament disruption producing carpal instability with scaphoid flexion and lunate extension (DISI), confirmed by widened scapholunate gap on grip radiograph and managed with primary repair or reconstruction.
