The thumb UCL is one of the most commonly injured ligaments of the hand, torn by forceful radial deviation of the thumb (skier's thumb from a fall onto a ski pole) or stretched by chronic stress (gamekeeper's thumb). It has a proper part to the proximal phalanx and an accessory part to the palmar plate. A Stener lesion occurs when the torn end of the ligament comes to lie superficial to the adductor pollicis aponeurosis, which blocks it from its insertion, prevents healing and mandates 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 |
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Resists radial deviation (valgus) stress at the thumb MCP joint, stabilising the thumb for pinch and grasp. The proper UCL is tightest in flexion and the accessory UCL in extension.
A Stener lesion is present in a large proportion of complete UCL tears and may be felt as a lump at the ulnar side of the MCP joint; ultrasound or MRI confirms it. Stress testing is done in both extension and about 30 degrees of flexion: laxity of more than about 30-35 degrees, or more than 15 degrees greater than the other thumb, without a firm endpoint indicates a complete tear. Complete tears and all Stener lesions are repaired surgically, ideally within a few weeks, usually with a suture anchor. Chronic tears may need reconstruction with a tendon graft such as palmaris longus.
Acute UCL rupture from forced MCP radial deviation, often with a Stener lesion that prevents spontaneous healing and requires surgical repair.
Chronic attenuation of the UCL from repeated radial stress, causing weak pinch and MCP instability, treated with reconstruction if symptomatic.
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