If you have skiers thumb or gamekeepers thumb, the ulnar collateral ligament (UCL) is damaged. The UCL is located on the inside of your thumb and helps to keep the joint stable. When this ligament is damaged, it can cause pain and swelling in the thumb joint. Treatment for skiers thumb or gamekeepers thumb usually involves wearing a splint or brace to immobilize the thumb and allow the ligament to heal. Surgery may also be necessary in some cases.