Wrist and hand

Scapholunate dissociation

Mechanism: Rupture of the scapholunate ligament, usually from a fall on the outstretched hand. Without that ligament the scaphoid tilts palmarly and the lunate dorsally, because they naturally want to move in opposite directions.
Recognition: Tenderness exactly distal to Lister's tubercle and a positive Watson test. On a loaded posteroanterior film a gap of more than three millimetres between the two bones is abnormal.
Course: Untreated it leads through a predictable sequence to wrist osteoarthritis, the SLAC pattern. Early recognition is therefore worthwhile, even though the test alone is not very specific.

Structures