A condition that affects the tendons in your finger or thumb, because of irritation and thickening of the tendon sheath tunnel, in which the flexor tendons of the finger and thumb slide through. Normally a snug tendon sheath covers the flexor tendons, which control movement and allow you to bend and straighten your fingers/thumb, keeping them in place. As the tendon sheath becomes irritated and thickened, it may become difficult for the flexor tendons to slide through the sheath tunnel. Specifically affected is the first annular (A1) pulley, which is located near the head of the metacarpal bones. Trigger finger results from the tendon becoming momentarily stuck, resulting in locking or catching of the affected finger/thumb while attempting to straighten. The most common symptoms of trigger finger include pain when bending/straightening finger, catching or locking sensation in affected finger/thumb, swelling, and possibly a tender lump in palm.