The flexor tendons of the fingers pass through several tunnels (sheaths) along the length of the fingers. In trigger finger, there is thickening of the tendon or tightening of the sheath. This prevents the tendon from smoothly moving through the sheath when the finger is flexed and extended, causing pain, stiffness, or catching symptoms. The most commonly affected part of the sheath is the first annular pulley (A1) at the metacarpophalangeal (MCP) joint. There may be a nodule on the tendon. When the finger is flexed, the nodule is outside the A1 pulley. As the finger is extended from a flexed position, the tendon nodule can get stuck at the entrance to the A1 pulley. This causes the finger to lock or get stuck in the bent position. It may release suddenly with a painful pop or click.
