Trigger thumb is a condition when the thumb is stuck in a bent position. Trigger thumb is typically caused by inflammation that narrows the space within the sheath that surrounds the tendon in the affected thumb. The thumb may straighten with a snap, like a trigger being released.
The flexor tendons that bend the fingers have a lining on the outside called tenosynovium. Trigger thumb is also called stenosing tenosynovitis.
Trigger thumb can occur if tendons enlarge, the lining increases in thickness, or soft tissue becomes larger which closes the opening for tendons. The extra friction on the moving tendons makes it difficult for the tendon to move back and forth. The condition is more frequent in women, diabetic patients, or people whose daily activities require repetitive gripping actions. A trigger thumb is a common and treatable problem.