Each digit of the hand has the ability to move freely throughout the OD in flexion and extension.
The efficiency, smoothness and strength of such movements become possible by several " pulleys" on the finger of the hand.
The trigger finger is thought to be caused by inflammation and subsequent narrowing of the A1 pulley of the affected digit, usually the third or fourth. The A1 pulley is most commonly affected, but there are some reported cases in which A2 and A3 pulleys have been affected. It can also appear in the thumb and then is called a thumb hammer. The difference in size between the flexor tendon shell and the flexor tendons can lead to abnormalities of the sliding mechanism, causing actual abrasion between the two surfaces, which leads to the development of progressive inflammation between the tendons and the shell.
Usually the triggerfinger is called "stenosing tenosinitis". However, there are histological studies that show that the inflammation occurs more in the tendon sheaths than in the tendosinium.
The trigger finger has a number of clinical manifestations. Initially, patients may have painless clicking during the movement of the phalanges. This can progress to a painful perception or popping, usually in the IFF or FIF.