Trigger Thumb

Stenosing tenosynovitis of the flexor pollicis longus tendon at the A1 pulley over the metacarpal head, where the thickened pulley and a nodule or thickening of the tendon prevent smooth gliding. The thumb catches, clicks or locks in flexion.

• It is a common cause of hand pain. Lifetime risk is about 2 to 3% in the general population and about 10% in diabetes. It is 2 to 6 times more common in women, and peaks at 40 to 60 years.
• Risk factors and associations: diabetes (higher risk, more resistant to treatment), rheumatoid arthritis, hypothyroidism, carpal tunnel syndrome, de Quervain tenosynovitis, amyloidosis, gout, renal failure with dialysis, repetitive or forceful gripping, and previous trauma.
• A congenital or paediatric form (a fixed flexion posture of the interphalangeal joint with a palpable nodule at the base of the thumb, often found at 1 to 3 years) occurs in about 0.05 to 0.3% of children, and the nodule is the thickened tendon.

• Pain at the base of the thumb on the palmar side, catching or clicking when the thumb is moved, a thumb that locks in flexion and snaps free (worse in the morning), and stiffness. A tender, palpable nodule over the A1 pulley at the metacarpal head moves with the tendon.
• Chronic cases: a fixed flexion contracture of the interphalangeal joint, and pain in the thumb interphalangeal joint or the forearm.
• Severity: grade 1 (pain and tenderness, no catching), grade 2 (catching, thumb moves actively), grade 3 (locking, passively correctable), grade 4 (fixed flexion contracture).
• Differential diagnosis: de Quervain tenosynovitis (radial wrist pain), carpometacarpal osteoarthritis, metacarpophalangeal arthritis, ganglion of the pulley, sesamoid pathology, ulnar collateral ligament injury, Dupuytren disease and septic flexor tenosynovitis.
• Red flags: fever, marked swelling and spreading redness with pain on passive extension (septic tenosynovitis, an emergency), a fixed deformity of recent onset after injury, and neurological loss.
• Complications: fixed flexion contracture, stiffness, loss of grip and pinch, tendon rupture (rare), and recurrence.

• Clinical, based on the nodule, catching and locking, and tenderness over the A1 pulley. No tests are needed in typical cases.
• Ultrasound shows a thickened A1 pulley and tendon, and fluid, and guides injection. X-ray if arthritis or fracture is suspected.
• Check HbA1c or fasting glucose in all patients with no known diabetes, thyroid function, and rheumatoid markers if multiple digits or other joints are involved.

• Conservative treatment for early disease (grades 1 and 2):
  • Activity modification, avoiding repetitive gripping and pressure over the palm.
  • A splint holding the metacarpophalangeal joint in 10 to 15 degrees of flexion (interphalangeal joint free), worn day and night for 6 weeks, with a resolution rate of about 50 to 70% in some series.
  • Paracetamol 1 g orally 6 hourly, short course ibuprofen 400 mg 8 hourly with food, or topical diclofenac 1% gel 2 to 4 g 3 to 4 times daily. Warm soaks and gentle tendon gliding exercises.
• Corticosteroid injection, first line invasive treatment: triamcinolone acetonide 10 to 20 mg (or methylprednisolone acetate 20 to 40 mg) with lidocaine 1% 0.5 to 1 mL, injected into the flexor tendon sheath at the A1 pulley (the tender nodule), with the needle angled at about 45 degrees and passed through the pulley. Ultrasound guidance improves accuracy. About 60 to 90% have lasting relief after the first injection, and about 50 to 60% in diabetes. A second injection after 4 to 6 weeks gives further benefit, and a third is used rarely. Risks: transient flare, skin atrophy and depigmentation, fat necrosis, infection, tendon rupture (rare) and a rise in glucose for 3 to 5 days in diabetes.
• Surgery for failure after 2 injections (or 1 in severe cases), a fixed contracture, or recurrence: release of the A1 pulley by open incision (transverse incision at the metacarpophalangeal flexion crease, with protection of the radial and ulnar digital nerves, which lie close and cross obliquely) or percutaneous release with a needle or blade. Success is about 95 to 100%. Complications: digital nerve injury (more likely with percutaneous release in the thumb), bowstringing if the oblique pulley is cut, infection, scar tenderness and stiffness. Recovery takes 2 to 4 weeks and early movement is encouraged.
• Paediatric trigger thumb: observe until 1 to 2 years of age, since about 30% resolve by age 1 to 2 and some later. Passive stretching and splinting have limited effect. Surgical A1 pulley release is done after about age 2 to 3 when there is a fixed flexion posture, and gives excellent results.
• Diabetes: control glucose, because steroid injection works less well and recurrence is higher, and surgery should be offered early if two injections fail.
• Special groups:
  • Pregnancy: splint and paracetamol, steroid injection if disabling (symptoms often resolve after delivery).
  • Rheumatoid arthritis: treat the disease, with flexor tenosynovectomy at surgery.
  • Dialysis and amyloidosis: recurrence is higher, so consider early surgery.
  • Anticoagulation: injection and percutaneous release are possible with local pressure.
  • Renal impairment and gastrointestinal disease: use topical agents in place of oral NSAIDs.
• Follow up: review at 4 to 6 weeks after injection. Refer to hand surgery for failed injections, fixed contracture, diagnostic doubt, or children after age 2 to 3.