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Trigger Finger

What is trigger finger?
Trigger finger is a common disorder of the hand which causes painful snapping or locking of the fingers or thumb. The medical name for this condition is stenosing vaginitis. Stenosing refers to the narrowing of an opening or passageway in the body. Tenosynovitis refers to inflammation of the outer covering of the tendons that bend and extend the fingers and thumb.

Overview of anatomy of trigger finger
The tendons are tough, fibrous cords that connect the muscles of the forearm to the bones of the fingers and thumb. This muscle and tendon system enables one to bend the fingers inward when making a fist, and extend them out straight.

The tendons glide through a protective covering called the tendon sheath. The sheath is like a tunnel, and is lined with a thin membrane called synovium. The synovial lining helps reduce friction as the tendons glide through the tendon sheath. Areas of dense fibrous tissue called annular bands or pulleys are also part of the tendon sheath. These strucutres are attached to the bones of the fingers and thumb, and hold the tendons close to the bones over which they pass.

Trigger finger is often caused by inflammation of the synovial sheath surrounding the tendons. It may also result from enlargement of the tendon itself or narrowing of the first annular band (A1 pulley).

When inflamed the normally thin covering of the sheath may be thickened to several times its normal size. This reduces the amount of space through which the tendons are able to pass. The tendon is no longer able to glide freely and may swell up in a balloon-like mass at the point where it tries to pass into the tunnel.

Upon forceful bending of the finger or thumb, the enlarged portion of the tendon is dragged through the constricted opening. This motion is often accompanied by a painful snap, and the finger or thumb may be locked in a bent position . Straightening the finger or thumb may require using the other hand to pull the finger back into an extended position, causing another painful snap as the swollen part of the tendon passes back through the sheath.

Triggering of the affected finger is due to flexor tendon swelling at the first annular pulley.

What are the causes?

The exact cause of trigger finger or thumb is not always readily apparent. In many cases, however, this condition may be the result of repeated strain of this area due to work or hobby activities. Tasks that require repetitive grasping or prolonged use of tools (scissors, screwdrivers etc) which press firmly on the tendon sheath at the base of the finger or thumb may irritate the tendons and result in thickening of the tendons themselves or the tendon sheath. Symptoms of trigger finger may also be associated with conditions such as rheumatoid arthritis , gout or metabolic disorders such as diabetes that produce changes in the connective tissues and synovium.

What are the signs and symptoms?
Before development of the actual “triggering”, the first sign may be discomfort in the palm beneath the affected finger. Painful clicking is the most common symptom. As the condition progresses the finger may become locked.

How is it treated?
Conservative (non-surgical) treatment is an appropriate first step unless the finger or thumb is in an unmovable, locked position. Initial treatment involves avoiding or modifying the activities that have caused the inflammation.

Oral anti-inflammatory medications may occasionally be used to reduce the inflammation or discomfort. Steroid injection may be administered directly into the tendon sheath to reduce the soft tissue swelling. The steroid takes several weeks to have its full effect.

In cases that do not respond to conservative treatment, or if the finger or thumb remain in a locked position, surgery may be recommended.

Surgery is performed on a day surgery basis under local anaesthetic and sedation. A horizontal incision is made in the palm at the base of the affected finger or thumb. The surgeon will release the first annular band, relieving the constriction of the tendon as it passes through the sheath. The patient may be asked to move the tendon to confirm that the triggering has been relieved.

In cases involving inflammation of the tendon lining such as arthritis, it may be necessary to remove the thickened synovial covering surrounding the tendon.

A light dressing is then applied to protect the wound but allow the finger to move. The dressing may be removed after five days. It is recommended that the wound be kept dry until the sutures are removed at 10-14 days following surgery. Activities requiring the use of the affected hand may be restricted for 4-6 weeks.