What is Trigger Finger?
Trigger finger is a common disorder of the hand that can cause pain, snapping or locking of the fingers or thumb. The sensation of locking or catching has often been referred to as triggering.
Tendons in the hand are strong cords that connect the muscle of the forearm to the bones of the fingers and thumb allowing them to bend the digits into a fist, as well as to straighten. Tendons are covered with a thin layer of tissue called tenosynovium which helps them glide through a protective tunnel called the tendon sheath. (Fig. 1) Certain areas of the tendon sheath are thickened forming specialized bands called pulleys which hold the tendon next to the bone, much like the eyes of a fishing rod hold the line near the rod.
Thickening of the tenosynovium or the tendon itself prevents the tendon from gliding freely within the tendon sheath. When the normal smooth gliding property of the tendon is lost, the digit becomes painful. As the tendon becomes larger, it can either become completely stuck inside the sheath preventing flexion of the digit into a fist or blocked from entering the sheath which may make it impossible to straighten the digit. (Fig. 2) This is often experienced by patients on awakening and may require the use of the other hand to pull the finger into a straightened position.
What are the causes?
A number of different factors can lead to thickening of the tendon or its tenosynovium. These include grasping or weight bearing on the hand, as when the use of a cane or crutches is required as well as with prolonged gripping with hand tools. Medical conditions such as diabetes, gout and inflammatory disease may contribute to this thickening.
What are the Signs and Symptoms?
Before the development of actual "triggering" (the painful snapping or locking of the finger or thumb), one of the first symptoms may be discomfort in the area of the palm directly beneath the affected finger of the thumb. This region marks the entrance of the tendon sheath or A1 pulley area.
The painful snapping sensation during finger motion is the most common symptom. As the condition progresses, the finger or thumb may actually become locked in a bent position, or less often in an extended position. The problem is sometimes incorrectly thought to exist in the middle joint of the thumb.
This joint may appear to jump or lock. The true problem, however, is found in the base of the finger or thumb. It is here that the smooth gliding of the tendon becomes obstructed.
How is it Treated?
When the finger or thumb is painful or triggering, initial treatment is to reduce the amount of thickening present in the tendon or tenosynovium. This may include the use of a splint worn at night, the use of anti-inflammatory medications or an injection of a cortisone preparation into the tendon sheath. These conservative measures usually reduce pain and triggering over the course of a few weeks.
In cases where a patient has chronic symptoms or a completely locked, painful and immovable digit, surgery may be recommended in lieu of non-operative measures.
Surgery is performed to enlarge the tendon sheath at its leading edge, which allows the tendon to again glide without locking or catching. A small incision is made is the palm in line with the affected digit. (Fig. 3) Once the tendon sheath has been enlarged, the patient is often asked to move their finger to confirm that triggering no longer exists.
Following the surgery, a light dressing is placed over the sutures. Movement of the affected digit should be performed several times a day to allow for recovery of normal motion. Recurrences of triggering are quite rare.
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