A sprain is an injury to a ligament.
Ligaments are the connective tissues that connect bones to bones across a joint.
These types of injuries are common in sports and falls. The thumb is jammed into another player, the ground, or the ball. The thumb may be bent in an extreme position, causing a sprain. The thumb will usually swell and may show bruising. It is usually very painful to move.
The most common ligament to be injured in the thumb is the ulnar collateral ligament. Injury to this ligament is sometimes called “skier’s thumb” because it is a common skiing injury. It occurs when the skier falls and the pole acts as a fulcrum in the hand to bend the thumb in an extreme position. This ligament may also be injured by jamming the thumb on the ground when falling or by jamming the thumb on a ball or other player. The radial collateral ligament may also be injured. It is much less commonly injured than the ulnar collateral ligament.