A sprained thumb, also referred to as skier's thumb, is a fairly common condition that involves damage of the connective tissues in the thumb. When the term "sprained thumb" or "thumb sprain" is used, it typically means an injury to the main ligament of the thumb.
Depending on the severity of the sprain, symptoms may or may not be felt right away. The most common symptoms of a thumb sprain are pain, swelling and tenderness at the base of the thumb over the ulnar collateral ligament. Pain is typically aggravated during activity or anything that causes the thumb to move backwards, though pain and stiffness may also occur during rest periods. In more severe sprained thumbs, swelling and bruising will develop almost immediately. These symptoms may be noticed on the front, back or sides of the affected thumb, and will collectively weaken your ability to grasp items between the thumb and index finger. When the injured thumb joint also feels lax and/or unstable, it may suggest a total rupture of the ligament, which requires surgery.