This is an injury to the ulnar collateral ligament of the metacarpo- phalangeal joint. This is a strong ligament that supports the thumb when pinching or gripping and if it is damaged may lead onto to a chronic instability of the thumb which causes problems with function.
Less often there is no specific injury and the cause is due to a chronic stretching of the ligament. This is referred to as a ‘gamekeeper’s thumb’. Patients with this problem complain of a loss of strength when pinching or gripping with the thumb.
The injury happens when you fall onto the outstretched thumb (see diagram)and is more likely if the thumb is gripping something at the same time. Falling when skiing while holding a ski pole is a common cause hence the name frequently given to this injury.
The thumb will be swollen, bruised and painful.