Ligament tear thumb. Skier's thumb or gamekeepers thumb are common terms for a tear in the thumb mp joint ulnar collateral ligament. The mechanism of injury is a radially-oriented force on the thumb, which can occur when gripping and planting a ski pole. (or, back in the day, ringing a rabbits neck.) best to see an orthopaedist or hand specialist for treatment options.
A ligament tear. Skiers thumb is a tear of the ulnar collateral ligament of the mcp joint. This is the main joint between the hand and the thumb at the web. Untreated leads to instability when grabbing or pinching.