Q: Can you give me a quick tutorial on "trigger fingers" -- what is it and what causes it? I know I have this problem because I have diabetes but I'm looking for a little more information than that.

A: Trigger finger is a condition affecting the movement of the flexor tendons as they bend the fingers toward the palm of the hand. This movement is called flexion. Triggering is caused by a mismatch between the size of the tendon with its covering or lining (called the tendon sheath) and the pulley system the tendon and its sheath glide through.

The tendons that move the fingers are held in place on the bones by a series of ligaments called pulleys. These ligaments form an arch on the surface of the bone that creates a sort of tunnel for the tendon to run in along the bone. To keep the tendons moving smoothly under the ligaments, the tendons are wrapped in a slippery coating called tenosynovium.

The tenosynovium reduces the friction and allows the flexor tendons to glide through the tunnel formed by the pulleys as the hand is used to grasp objects. The constant irritation from the tendon repeatedly sliding through the pulley causes the tendon to swell in this area and create the nodule. This inflammation and swelling of the tendon sheath or the pulley leads to pinching of the tendon. The tendon fibers start to bunch up causing a nodule to form.

Symptoms of trigger finger include pain and a funny clicking sensation when the finger is bent. The clicking sensation occurs when the nodule moves through the tunnel formed by the pulley ligaments. With the finger straight, the nodule is at the far edge of the surrounding ligament.

When the finger is flexed, the nodule passes under the ligament and causes the clicking sensation. If the nodule becomes too large it may pass under the ligament, but it gets stuck at the near edge. The nodule cannot move back through the tunnel, and the finger is locked in the flexed trigger position. Pain occurs when the finger is bent and straightened. Tenderness occurs over the area of the nodule.

People with diabetes often develop hand problems because of the effect of elevated sugar in the blood (elevated blood glucose). Glucose deposits along the tendons and ligaments result in loss of flexibility and rigidity.

Flexor tenosynovitis (also called chronic stenosing tenosynovitis) is one of those problems seen more commonly in persons with diabetes. Tenosynovitis is caused by accumulation of fibrous tissue in the tendon sheath and can cause aching, nodularity along the flexor tendons, and contracture.

Trigger finger can occur in flexion or extension with tenosynovitis and may be associated with crepitus or pain. In the population with diabetes, tenosynovitis is found predominantly in women and affects the thumb, middle, and ring fingers most often.

Reference: Hussain Shakeel, MBBS, and T. Sara Ahmad, MBBS. Steroid Injection Versus NSAID Injection for Trigger Finger: A Comparative Study of Early Outcomes. In The Journal of Hand Surgery. July 2012. Vol. 37A. No. 7. Pp. 1319-1323.