A trigger finger is caused by a small nodule on the flexor tendon, which interferes with the smooth gliding of the tendon within its sheath or tunnel. When the finger is flexed, the nodule emerges from the tunnel, and as the finger is extended, the nodule catches on the free edge of the tunnel, causing it to catch. This catching can be mild, or it can prevent finger extension altogether.
Trigger finger is a common condition, more prevalent in patients with diabetes. In simple cases, the triggering will resolve with up to 3 steroid injections into the flexor sheath. If this appoach fails, or if the triggering is severe, then an operation is recommended.
The operation is usually done under a local anaesthetic, and involves dividing the free edgs of the tunnel, to allow free gliding of the tendon.