A Sprained Thumb: What Is It? Unlike a thumb fracture (break), which affects the bone, a sprained thumb affects the ligament, which is a soft tissue that stabilizes the joints by connecting bones. The thumb ligament that sustains injuries the most is the ulnar collateral ligament. The thumb and the hand on the side that is next to your index finger are joined by this specific ligament. Thumb sprains are frequently caused by falls or sports-related injuries. For instance, thumb injuries are common in contact sports like basketball and volleyball. In volleyball, setting the ball torques the thumb as well. A common injury to the thumb is an ulnar collateral ligament (UCL) tear; also called “skier’s thumb” or “gamekeeper’s thumb”. Symptoms of a Sprained Thumb So, is it just a jammed finger, a broken thumb, or a sprained thumb? The following five indications point to a sprained thumb: 1. Bruising 2. Swelling 3. Pain 4. Weakness 5. Difficulty carrying out routine tasks as ...