<P> Gamekeeper's thumb and skier's thumb are two similar conditions, both of which involve insufficiency of the ulnar collateral ligament (UCL) of the thumb . The chief difference between these two conditions is that Skier's thumb is generally considered to be an acute condition acquired after a fall or similar abduction injury to the metacarpophalangeal (MCP) joint of the thumb, whereas gamekeeper's thumb typically refers to a chronic condition which has developed as a result of repeated episodes of lower - grade hyperabduction over a period of time . Gamekeeper's thumb is more difficult to treat because the UCL has lengthened and become thinner as a result of repeated injury . It is moderately painful compared to similar injuries . </P> <P> In addition to skiing, this injury (resulting from forced abduction or hyperextension of the proximal phalanx of the thumb) is seen in a wide variety of other athletic endeavors . The most common mechanism of injury appears to be when a person extends the arm in an attempt to block a fall . The stress resulting from falling onto an abducted thumb produces a valgus force on the MCP joint of the thumb, resulting in a sprain or tear of the UCL . </P> <P> In a recent study, 49% of UCL disruptions of the thumb were caused by a fall onto an outstretched hand . Sports injuries accounted for most of the remaining injuries, with only 2.4% acquired as a result of skiing injuries . </P> <P> The ulnar collateral ligament is an important stabilizer of the thumb . Thumb instability resulting from disruption of the UCL profoundly impairs the overall function of the involved hand . Because of this, it is critical that these injuries receive appropriate attention and treatment . </P>

What is the name of the thumb joint