Stenosing tenosynovitis, also known as trigger finger, is a medical condition in which a finger or thumb seems to be “stuck” in a bent position, until it snaps back suddenly into place. It most frequently occurs in middle age or older women.
Each finger and the thumb have flexor tendons that extend along the inside of the finger, from the base of the palm to the fingertip. These tendons give the fingers power to bend, curl, and grip objects. The tendons are protected and held in place by tendon sheaths, which encase sections of the tendon. When these sheaths become inflamed, they can constrict the space available for the tendon to slide through them. Occasionally a small bump, or nodule, can also form, making the constriction even worse.
Trigger finger has no known cause, but factors that experts suspect may trigger it include repetitive or forceful hand movements, previous injury, or chronic inflammation.
Arush A. Patel, M.D., Trigger Finger (Stenosing Tenosynovitis), Arthritis-Health (updated Mar. 15, 2018)