Gamekeepers thumb is

Injury to the thumb metacarpophalangeal joint ulnar collateral ligament is commonly referred to as gamekeeper thumb or skier's thumb, although the original "gamekeeper" description (Campbell, 1955) referred to an attritional ulnar collate-earl ligament injurySnow skiing accidents and falls on an outstretched hand with forceful radial and palmar abduction of the thumb are the usual cases(Refer: Mohindra's Fundamentals of Ohopedics, 2nd edition, pg no. 177, 495)