Trigger finger

The tendons that bend your fingers (flexor tendons) start at the forearm muscles, pass through the palm, and attach to the finger bones. Ring-shaped structures called pulleys hold these tendons close to the bones so they do not lift away. Pulleys labeled A1 through A5 are arranged in an alternating pattern along each finger, and a thin sheath (Tendon sheath) surrounds the tendon as it glides through this passage.

The first pulley on the palm side, just below the joint at the base of the finger (the metacarpophalangeal joint), is the A1 pulley. If the tendon swells or the pulley thickens and narrows the passage, the tendon catches at this point. Bending and straightening the finger produces a clicking sound and a catching sensation. The name “trigger finger” comes from the way the finger suddenly snaps straight, like the trigger of a gun. The Sino-Korean term for it means “a finger that snaps out.”

Its formal medical name is “stenosing flexor tenosynovitis.” This refers to a tendon sheath problem involving a narrowed passage (stenosis). When it affects the thumb, it is specifically called trigger thumb. It is reported to occur commonly in the thumb, middle finger, and ring finger.

The key issue is a mismatch between the thickness of the tendon and the size of the passage at the A1 pulley. If the tendon becomes thicker or the pulley thickens, friction increases, and that friction leads to further swelling.

Studies examining the tissue describe a change called fibrocartilaginous metaplasia in the ligamentous layer of the A1 pulley, where high forces are repeatedly applied, narrowing the cross-section of the passage. Although the condition’s name includes “-itis,” meaning inflammation, it is closer to a tissue adaptation to repeated friction.

Associated factors discussed include the following.

• Repeated gripping — Activities involving frequent forceful gripping or prolonged use of tools and devices.
• Systemic conditions — Diabetes is a prominent example, and rheumatoid arthritis and other conditions are also discussed.
• Age and sex — It is relatively common in women and from middle age onward.
• Coexisting hand conditions — It may occur alongside Carpal tunnel syndrome or De Quervain tenosynovitis. De Quervain tenosynovitis is a similar type of condition in which tendons on the thumb side of the wrist catch within their passage.

Cases are sometimes divided into those without a particular underlying condition and those associated with a condition such as diabetes.

At first, the palm side near the base of the finger may ache or hurt when pressed, and you may feel a small lump. A catching sensation then develops when you bend and straighten the finger.

• It is stiffer in the morning. A typical pattern is more pronounced catching just after waking, which gradually eases as you move your hand.
• The finger locks in a bent position. It may stay bent until you use your other hand to push it straight.
• Movement becomes limited. As the catching becomes more severe, bending or straightening the finger itself becomes difficult.

The severity and course vary considerably from person to person. Mild catching may go away, or it may gradually become more noticeable.

A cracking sound from a finger joint is Finger joint cracking, caused by bubbles forming and disappearing in the joint fluid. This is different from trigger finger, in which a tendon catches. The distinguishing feature is whether catching, snapping, and pain occur together.

• Give your hands time to rest. If you spend a long time gripping in the same way, take breaks to open and rest your hands.
• Try thicker handles. Thick or cushioned tool and pen handles reduce the effort your fingers need to exert.
• Reduce your grip force. Check whether you habitually grip more tightly than necessary, and support bags or heavy objects with your whole palm or your arm.
• Warm up your hands in the morning. Soaking your hands in warm water and then slowly bending and straightening your fingers can ease morning stiffness.
• Do not force the finger straight. Rather than pulling hard on a locked finger, gently support it with your other hand.
• Adjust your smartphone and mouse use. Try to reduce the time you spend with your fingers held bent.

In a clinical setting, treatment is tailored to the degree of tendon catching and your daily activities. Options include rest, splinting, steroid injections, and surgery to release the pulley.

• Your finger is locked in a bent position and is difficult to straighten even with your other hand.
• The same symptoms occur in several fingers or both hands.
• A lump in your palm is getting larger, or there is warmth and swelling.
• You have diabetes and repeated finger catching.
• It is increasingly interfering with daily life and work.

For related descriptions, see Finger stiffness. For swelling around the finger joints, see Finger joint swelling, and for fluid-filled lumps in the hand and wrist, see Ganglion cyst.