What is skier's or gamekeeper's thumb?
The middle joint of the thumb (the MCP joint) needs to be stable to provide a strong pinch.
If the ligament on the inside of the MCP joint is torn (for example by getting caught behind a skiers pole or bicycle handle bars), the joint becomes unstable. It is a common injury, but is often first dismissed as a sprain only.
Treatment for skier's & gamekeeper's thumb
Ideally, treatment of skiers thumb is done early after the injury. The ligament can then be repaired directly.
If the injury has been present for a while, a reconstruction of the ligament using a spare tendon from the forearm may be necessary.