A painful condition that causes catching or locking of a finger as it is extended. Trigger finger is due to overgrowth of tissue in the tendon sheath (the protective membrane) of the flexor muscles, the muscles that ordinarily allow fingers to curl. Also called flexor tenosynovitis, trigger finger is a fairly common complication of diabetes, especially long-standing diabetes. It is thought that chronically elevated blood glucose levels cause the connective tissue to become glycated, meaning that irreversible bonds between glucose and proteins form in the tissue, damaging it. Trigger finger is initially treated by injecting corticosteroids into the flexor tendon sheath. If this fails to completely alleviate the problem, minor surgery may be needed to provide permanent relief.