The ulnar collateral ligaments are strongs band that is attached to the joints of the finger. Injury to this ligament is commonly due to any hard force put on the finger that causes the finger to be bent too far sideways, usually a result of a sports related injury. This force can result in a partial tear of the UCL (ulnar collateral ligament) or a complete tear of the UCL, known as a rupture. A tear to the UCL results in instability of the affected joint of the finger becoming very unstable and painful. The most common symptoms associated with UCL injuries are swollen, painful joint, and possible deformity of the finger, as well as bruising.