The scapholunate ligament is the most commonly injured intrinsic carpal ligament. Its rupture leads to a characteristic radiographic finding on PA wrist X-ray. What is this finding?

• A Gilula's arc disruption at the midcarpal joint with lunate dislocation
• B Foreshortened capitate overlapping the lunate (capitolunate instability)
• C Terry-Thomas sign: widened scapholunate gap (>3 mm) due to rotatory subluxation of the scaphoid ✓
• D Increased carpal height ratio due to proximal migration of capitate

Explanation

Scapholunate ligament disruption allows the scaphoid to flex volarly and the lunate to extend (DISI — dorsal intercalated segment instability). On PA radiograph this produces the Terry-Thomas sign: a gap of >3 mm between the scaphoid and lunate (named after the gap-toothed comedian). Gilula's arcs trace the proximal and distal carpal rows on PA; disruption suggests perilunate or lunate dislocation, which are more severe injuries. A decreased carpal height ratio, not increased, occurs with severe carpus collapse.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.