The ulnar collateral ligament (UCL) of the thumb MCP joint runs from the ulnar condyle of the first metacarpal head to the ulnar base of the proximal phalanx (proper UCL, primary restraint) and to the volar plate (accessory UCL). The UCL is the primary restraint to radial deviation of the thumb MCP joint and is critical for pinch strength. A Stener lesion occurs when the completely torn UCL retracts proximally above the adductor pollicis aponeurosis, preventing healing.
Primary restraint against radial deviation (valgus stress) of the thumb MCP joint; the proper UCL provides resistance throughout the flexion arc with maximum tension at approximately 30 degrees flexion; the accessory UCL provides additional restraint in extension.
Gamekeeper's thumb (chronic UCL insufficiency from repetitive valgus stress on the thumb MCP) and skier's thumb (acute UCL rupture from ski pole impact producing forced thumb MCP radial deviation) are the two clinical entities involving the thumb UCL. Complete UCL rupture (positive valgus stress test at 30 degrees with 35+ degrees laxity compared to contralateral) is treated surgically. Stener lesion (complete UCL interposition beneath the adductor pollicis aponeurosis) prevents healing and is an absolute indication for operative repair. UCL repair with suture anchors or reconstruction with palmaris longus graft is performed for acute and chronic complete tears respectively.
Complete UCL tear allows the ligament to retract proximally and become entrapped beneath the adductor pollicis aponeurosis, preventing healing in anatomical position; MRI confirms the Stener lesion as the characteristic proximal rounded low-signal mass lateral to the adductor aponeurosis; operative repair through a medial thumb incision repositions the UCL and secures it to the proximal phalangeal base with a suture anchor.
