Rare Case of Trigger Finger
Trigger finger is a catching or popping of the tendons as they move the fingers. Usually this problem occurs as the finger is moved toward the palm of the hand. This movement is called flexion. But in this article, five cases of extensor tendon triggering are reported.

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 tendons to glide through the tunnel formed by the pulleys as the hand is opened to release objects.

Triggering is usually the result of a thickening in the tendon. Constant irritation from the tendon repeatedly sliding through the pulley causes the tendon to swell in this area. A nodule or knob forms. The pulley ligament may thicken as well. The nodule catches on the pulley causing the popping or catching sensation.

Sometimes, a thickening in the band of connective tissue across the back of the wrist is the cause of the problem. This area is called the extensor retinaculum. Even minor changes in the tendon can cause catching of tendon as it tries to glide under the retinaculum.

The authors present each of the five cases in detail. History, clinical presentation, diagnosis, treatment, and outcomes are reviewed and discussed. Each patient had an extensor tendon trigger of either the index or small finger. These two fingers are referred to as the border digits. Each one is along the outer border (outside edge) of the extensor retinaculum.

There was no single reason for the impingement causing the triggering. In one case, there was a lump in the index finger extensor tendon. The retinaculum was also thickened. In the second case, the patient had a ganglion in the tendon. Each time the tendon tried to slide and glide under the retinaculum, the ganglion would get caught on the edge of the retinaculum.

Another patient had a tightening of the sheath around the tendon. Two others demonstrated thickening of the extensor retinaculum but no other visible cause and no apparent reason for the thickening. The reported findings were observed during surgery that was done in order to identify and correct the problem.

In one patient, the area of tendon thickening was so small, the surgeons were surprised that releasing the retinaculum took care of the problem completely. This same patient presented again six months later with the same problem in the other hand three years later. After surgery, the five patients recovered fully. They had full function, no symptoms, and no complications.

The authors conclude that a mismatch between the size of the tendon and the area through which it must move can result in catching of the tendon called trigger tendon as described. Patients' reports of pain, popping, and clicking are relieved when surgery is done to correct the problem.

Most of the time, trigger finger affects fingers on the palmar side of the hand. In these rare cases, the same problem occurred along the extensor (back side) surface of the hand. Extra slips of tendon, thickening within the tendon or retinaculum, or inflammation of the lining of the tendon can all contribute to the development of extensor tendon triggering.

There probably isn't a single factor leading to this problem. With so many tendons and other soft tissues passing through such a small space, it's more likely there are many reasons for this condition. Surgery is usually successful both in identifying more specifically what's causing the problem and in fixing it.
Michael Khazzam, MD, et al. Extensor Tendon Triggering by Impingement on the Extensor Retinaculum: A Report of 5 Cases. In The Journal of Hand Surgery. October 2008. Vol. 33-A. No. 8. Pp. 1397-1400.