A trigger finger or trigger thumb is a condition in which the movement of the affected digit is arrested for a moment while flexed or extended, and then continues with a jerk upon continued effort. This irregularity results from thickening and constriction of the mouth of the fibrous tendon sheath through which the affected tendon travels. The thickened sheath interferes with the normal, free glide of the flexor tendon within, and the tendon develops a swollen area as a result. Trigger finger occurs most commonly in the ring or middle fingers, and most commonly affects the fingers of middle-aged women and the thumb in infants or small children. It has been known to cause disability in long-term diabetic patients.