Trigger fingers occur when the tendon that bends the finger becomes inflamed and a nodule or bump forms. As it passes through narrowings within the tendon sheath called pulleys, these nodules catch causing pain, clicking and sometimes locking of the finger. The most common site is at the pulley at the base of the fingers or thumb.
Rest, splinting and steroid injections can sometimes help. A minor procedure, where the pulley is released is sometimes required.