Trigger Finger (Stenosing Tenosynovitis)

What Is Trigger Finger?

Trigger finger, medically known as stenosing tenosynovitis, is a condition that affects the tendons in the fingers or thumb, causing pain, stiffness, and a characteristic catching or locking sensation when attempting to bend or straighten the affected digit. The condition gets its name from the triggering or snapping movement that occurs as the finger suddenly releases from a bent position, similar to pulling and releasing a trigger. This distinctive symptom results from inflammation and thickening of the tendon sheath through which the flexor tendons must glide during normal finger movement.

To understand trigger finger, it's helpful to understand normal finger anatomy. The flexor tendons run along the palm side of each finger, connecting the forearm muscles to the bones of the fingers. These tendons allow the fingers to bend and grip. The tendons are surrounded by a protective sheath lined with synovium, a membrane that produces lubricating fluid allowing smooth tendon gliding. Along the length of each finger, there are several pulleys (annular ligaments) that hold the tendons close to the bone, much like guides on a fishing rod hold the line. These pulleys are essential for efficient finger motion—without them, the tendons would bow outward when the finger bends, reducing mechanical efficiency.

When trigger finger develops, inflammation causes the tendon sheath to thicken and the space within it to narrow. Additionally, a nodule or knot may form on the tendon itself. As the finger bends, this swollen tendon or nodule must pass through the narrowed space under the pulley at the base of the finger (specifically, the A1 pulley). When the space is tight enough, the tendon may become momentarily stuck as it tries to pass through. This creates the sensation of catching. When enough force builds up, the tendon suddenly pops through the constriction with a snapping sensation—the trigger effect. Each time this happens, more inflammation develops, worsening the problem and creating a cycle where the catching becomes progressively more frequent and severe.

The causes of trigger finger are not completely understood, though several risk factors have been identified. Repetitive gripping activities can lead to tendon irritation and inflammation. People whose occupations or hobbies involve prolonged or forceful gripping—such as musicians, craftspeople, farmers, or industrial workers—are at increased risk. Women are more commonly affected than men. The condition most frequently appears in people between 40 and 60 years of age. Patients with certain medical conditions are more vulnerable. Diabetes significantly increases risk, with up to 20 percent of diabetic patients developing trigger finger at some point. Rheumatoid arthritis and gout also increase susceptibility. Carpal tunnel syndrome and trigger finger often occur together, suggesting some common underlying factors.

Trigger finger usually starts with discomfort at the base of the affected finger or thumb, typically where the finger meets the palm. This area may feel tender to touch. As the condition progresses, patients notice stiffness, particularly upon waking in the morning or after periods of inactivity. The palm-side base of the finger may begin to feel thickened, and a small nodule may be palpable. Eventually, the characteristic catching or locking develops. The finger may lock in a bent position, requiring the other hand to straighten it, or it may lock in a straight position, making bending difficult. The triggering can be painful, causing a sharp sensation as the tendon snaps through the constriction. While it can feel like the problem is located at the middle knuckle where the locking seems to occur, the true cause is at the base of the finger where the tendon passes through the pulley. The ring finger and thumb are most commonly affected, though any digit can be involved, and multiple fingers can be affected simultaneously.