The thumb UCL is the most commonly torn ligament in the hand, injured by forceful radial deviation of the thumb (skier's thumb from ski pole fall, gamekeeper's thumb from chronic stress). Stener lesion occurs when the torn UCL end folds back beneath the adductor pollicis aponeurosis, preventing spontaneous healing and mandating surgical repair.
| Origin | Medial (ulnar) aspect of the first metacarpal head |
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| Insertion | Ulnar base of the proximal phalanx and volar plate of the thumb MCP joint |
| Actions | Primary restraint against radial deviation (valgus) stress at the thumb MCP joint — the main lateral stability ligament for pinch |
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Stener lesion (present in 50-80% of complete UCL tears) is identified by a palpable mass at the ulnar MCP level (the displaced UCL end under the aponeurosis) and confirmed by ultrasound or MRI. Complete UCL tears with Stener lesion require surgical repair within 3-6 weeks. Radial stress at 30 degrees of MCP flexion greater than 30 degrees compared to the other side confirms instability.
UCL rupture from forced MCP radial deviation, with Stener lesion in 50-80% preventing spontaneous healing and requiring surgical repair.
