Thumb UCL Injury

Thumb ulnar collateral ligament (UCL) injury is a tear of the ligament on the ulnar side of the thumb metacarpophalangeal (MCP) joint, caused by forced radial deviation (abduction) of the thumb.

It is often called skier's thumb, after a fall holding a ski pole, but in a UK series of 127 surgically treated patients falls were the commonest cause and skiing accounted for only 2.4%. Gamekeeper's thumb describes the older pattern of chronic attrition.

The key decision is whether the joint shows significant laxity, which suggests a complete tear, and whether the torn ligament has displaced into a Stener lesion. A missed complete tear can leave chronic instability, weak pinch and later MCP arthritis.

The UCL has 2 parts that run from the metacarpal head to the volar-ulnar base of the proximal phalanx:

• •The proper collateral ligament, taut in MCP flexion
• •The accessory collateral ligament, taut in MCP extension, working with the volar plate

The adductor aponeurosis, from adductor pollicis, lies superficial to the UCL. In a Stener lesion the torn distal end of the ligament retracts and comes to lie superficial and proximal to the aponeurosis, which then sits between the ligament and its insertion and stops it healing.

Injuries range from a partial tear with a stable joint to a complete tear, with or without a Stener lesion, and may include a bony avulsion from the base of the proximal phalanx. UK guidance (BSSH 2024) bases management on whether there is significant laxity rather than on the older grading alone.