Trigger finger results from tendon inflammation.  The tendons that bend the finger enter a tunnel system in the palm.  For reasons that are not well-understood, the tendon can  become inflamed which is felt as a nodule in the palm.  When the finger is bent, the tendon gets stuck and the finger is locked in a bent position.

Treatment typically requires an injection of cortisone.  One or two injections gives relief in most cases.  Approximately 20% of people will need a minor surgery to open the tunnel.  In diabetic patients, the injections are less effective and work only about 50% of the time.