In a normally functioning finger, the flexor tendon travels within a fibrous retinacular sheath. The retinaculum stabilizes the tendon against the bone with five separate straps that act as pulleys. The fibrous pulleys allow the tendon to slide freely between the retinaculum and bone as the finger flexes and extends.
In trigger finger, however, inflammation of the most proximal pulley, the A1 pulley, leads to a narrowing of the retinacular canal, preventing the flexor tendon from sliding freely. This leads to a painful "popping" or "clicking" sensation when the affected finger is extended. Less commonly, the condition presents as stiffness without popping or locking.
Trigger finger is common, with a lifetime risk in adults of 2%-4%. Women are affected 6 times more often than men are. People with diabetes have a higher risk of developing the disorder and are more resistant to treatment. The disorder is also seen more frequently in patients with rheumatoid arthritis, carpal tunnel syndrome, amyloidosis, hypothyroidism, and de Quervain tenosynovitis. While most cases are idiopathic, repetitive hand use, such as in manual labor or constant texting, is a risk factor for developing the condition.
The disorder may initially be painless, with the patient first noticing a clicking sensation when using the affected finger. As the retinaculum becomes more inflamed, pain occurs with digital flexion and extension. A tender nodule may develop at the metacarpophalangeal (MCP) joint proximal to the affected finger, further inhibiting the flexor tendon from sliding in and out of its retinacular sheath. Eventually, the patient loses the ability to actively extend the digit and will present with the finger in locked flexion. If untreated, contractures of the proximal interphalangeal joint may develop.
Trigger finger in adults should be distinguished from the less common pediatric condition of developmental trigger thumb, which presents before the age of 4 years at a rate of 1-3 children in 1000. Pediatric trigger finger occurs in the same age group as trigger thumb but is 10 times less common and is often related to underlying anatomic anomalies or medical conditions. It most frequently affects the third digit.
M65.30 – Trigger finger, unspecified finger
12121000119102 – Congenital trigger finger and trigger thumb
1539003 – Acquired trigger finger
Differential Diagnosis & Pitfalls
- Dupuytren contracture
- Ganglion cyst
- Rheumatoid arthritis / Bouchard node
- Focal dystonia
- Flexor tendon / sheath tumor
- Sesamoid bone anomalies
- Post-traumatic tendon entrapment on the metacarpal head
- MCP osteoarthritis
- MCP joint sprain
- Fracture or dislocation – Will have swelling and reduced range of motion; x-ray can rule out.
- Developmental loss of extensor tendon (in children)