Trigger finger occurs when the finger or thumb tends to lock or stick as the finger is flexed into and out of the palm. Tendons that flex the finger into the palm run in tunnels called flexor sheaths and are surrounded by a membrane that helps them to glide up and down the tunnel. Trigger finger happens when the tendon is thickened or has a nodule on it. This causes the tendon to stick at the firmer parts of the tunnel and temporarily lock.
A steroid injection can allow the tendon to glide freely again but if this is not sucessful surgical release of the tunnel at the site of the blockage can be done. It is done through a small incision in the palm of the hand near the base of the finger. A slit is made at one of the thickened areas in the flexor sheath and the tendon no longer catches at this site.