<prompt> Gamekeepers thumb is?Ulnar collateral ligament injury of MCP jointRadial collateral ligament injury of CMC jointRadial collateral ligament injury of MCP jointUlnar collateral ligament injury of CMC joint  <response>: It is sprain or rupture of ulnar collateral ligament UCL of first metacarpophalangeal joint. It is the most common injury of MCP joint. This injury occurs when the thumb is forced into radial detion stressing the ulnar collateral ligament. The interaction between the thumb and first web space with skie pole grips has been blamed for the associated UCL rupture in this spo. When UCL tears from its phalangeal inseion, the adductor pollicis aponeurosis may become interposed between the retracted ligament, preventing healing of the ligament to the proximal phalanx with closed treatment steners lesion Ref: Current Diagnosis Treatment in Ohopedics 3e, page 565-66; Apleys 8e, page 635; Rockwood Greens fracture in Adults 6e, Page 17. 