By Dr. John Roberts
I’ve had a run of patients recently, all presenting with problems getting their fingers to move. They all described pain with “catching” or “popping” when trying to flex or extend a finger. They were suffering from trigger finger, a condition also known as trigger digit or by the medical term stenosing tenovaginitis.
The condition is very common. It is seen two to six times more frequently in women than men and typically starts showing up around 55 to 60 years of age. It is also seen more often in a person’s dominant hand. It can affect any of the fingers, most often the thumb, followed by the ring , middle , little and index fingers.
The reasons for developing trigger finger are not completely understood. It seems to be associated with activities that require pressure on the palm during powerful gripping or repetitive forceful flexion of the fingers such as when using heavy shears. Unlike carpal tunnel syndrome, the increased use of keyboards in our society does not seem to have caused an increased incidence of the condition.
There are other medical conditions that raise the risk for developing trigger finger. It is more common in those suffering from rheumatoid arthritis and diabetes. People who have psoriatic arthritis, amyloidosis, hypothyroidism and sarcoidosis are also at higher risk.
The symptoms and signs of trigger finger are easy to spot. Patients experience the catching or popping sensation when flexing or extending their fingers. Some may even experience locking of the finger when it gets stuck, usually in the flexed (finger down) position. Most patients also have pain in the palm next to the base of the involved finger.
Trigger finger can be easily understood when one looks at the anatomy involved during finger motion. Finger movement happens when muscles in the forearm contract, pulling on the finger bones. The muscles are attached to the bones by tendons.
The culprit in trigger finger is one of the flexor tendons on the palm side of the hand, the flexor digitorum superficialis or FDP. In order for these tendons to work properly they have to slide through connective tissue tubes called tendon sheaths and under little tissue bridges called retinacular pulleys. To visualize this, think of a rope that is running through a pulley to pull an object on the other side.
The anatomic problem that occurs in trigger finger is caused by the development of a swollen area on the FDP tendon that can sometimes be felt. Returning to my rope and pulley analogy, this would be equivalent to having a knot in the rope that can’t pass through the pulley so it gets stuck.
If it’s a small knot, with a little force you can go ahead and pull it through. A larger knot gets stuck and you can’t pull the rope through the pulley. This is exactly what happens in trigger finger – as the swelling on the tendon gets larger it becomes harder to move it through the retinacular pulley and sometimes it can get permanently stuck on one side.
If the enlargement in the tendon gets stuck on the wrist side of the retinacular pulley, the finger can’t be extended and gets stuck in the flexed, or down position. If it gets stuck on the palm side, the finger gets stuck in the extended, or up position and can’t be flexed.
Treatment for trigger finger is fairly straightforward. First line therapy is to try and shrink the swelling in the tendon by injecting a steroid solution into the tendon sheath surrounding the FDP tendon. This procedure can be performed in most physician’s offices using a small needle.
Steroid injections are successful about 85 percent of the time. They are more successful in women, those who have had symptoms less than four months and who have a single swollen area in the tendon. It is less successful in those who have other conditions such as rheumatoid arthritis and diabetes.
Sometimes a second injection is needed. If a person fails two injections, surgery is indicated. It is a simple outpatient procedure that involves cutting the retinacular pulley to allow the tendon to move freely.