Trigger Finger limits finger movement. It may be difficult to straighten the finger because it locks or catches, before suddenly extending. The condition affects the tendons of the fingers and thumb.The tendons glide in tunnels called tendon sheaths. If the tendon becomes inflamed, it swells and is not able to glide smoothly in the sheath. Eventually there is thickening of the tendon, and the opening of the tunnel becomes smaller. Surgery is required if non-surgical methods such as steroid injection have not worked. Surgery widens the tunnel to allow tendon gliding.