Trigger Finger

Trigger finger (stenosing flexor tenosynovitis) is catching or locking of a finger or thumb as the flexor tendon passes through a narrowed first annular (A1) pulley at the metacarpal head. The pulley thickens with fibrocartilaginous metaplasia and the tendon develops a nodule, so the nodule clicks through the pulley in flexion and may lock.

The lifetime risk is 2 to 3% in the general population and up to 10% in people with diabetes. It is 2 to 6 times more common in women, peaks at 40 to 60 years, and most often affects the ring finger and thumb. Associations are diabetes (with more frequent multiple digits, and poorer response to injection), rheumatoid arthritis, hypothyroidism, gout, amyloidosis, carpal tunnel syndrome and Dupuytren contracture.

Grading: I pain and tenderness with no catching, II catching that the patient can correct actively, III catching that needs passive correction, IV fixed flexion contracture. Congenital trigger thumb (a flexor pollicis longus nodule, typically noticed between 6 months and 3 years) is a separate childhood form. Complications are fixed proximal interphalangeal flexion contracture, stiffness and recurrence.

• Painful clicking or catching of a digit, locking in flexion especially in the morning, with a need to straighten the finger with the other hand
• Tender, palpable nodule on the palm at the metacarpophalangeal flexion crease, which moves with the tendon
• Fixed flexion of the proximal interphalangeal joint in advanced disease
• In children: the thumb interphalangeal joint is fixed in flexion, with a palpable nodule at the metacarpophalangeal joint (Notta node)
• Red flags: warm, swollen, painful finger with pain on passive extension and a fusiform swelling (flexor sheath infection), trauma, multiple digits with systemic disease, and a stiff digit with no triggering

• Clinical diagnosis from the catching and the palpable nodule.
• Ultrasound (optional): thickened A1 pulley, nodule, sheath fluid and dynamic triggering.
• HbA1c, thyroid stimulating hormone and inflammatory markers when several digits are involved or the disease is recurrent.
• Radiographs when arthritis or trauma is suspected.

Differentials: Dupuytren contracture, flexor sheath infection, metacarpophalangeal arthritis, sesamoiditis, pulley ganglion, volar plate injury, fracture, interphalangeal contracture of other cause.

• Activity modification and splinting: a metacarpophalangeal joint blocking splint holding the joint at 10 to 15 degrees of flexion, worn at night and during activity for 6 weeks.
• Analgesia: paracetamol 1 g orally every 6 hours, and ibuprofen 400 mg orally every 8 hours with food for up to 7 days.
• Corticosteroid injection: triamcinolone acetonide 10 mg (or methylprednisolone acetate 20 mg) with lidocaine 1% 1 mL into the flexor sheath at the A1 pulley level. Success is about 60 to 90% in non-diabetic patients and 50 to 60% in diabetics. A second injection may be given after 6 weeks, and a third at most. In diabetic patients monitor blood glucose for 3 to 5 days. Adverse effects: skin atrophy and depigmentation, tendon rupture, infection.
• Surgery (after 2 injections, for grade IV disease, recurrent triggering, or multi digit disease in diabetes):
  • Open A1 pulley release through a transverse palm incision, protecting the digital nerves, under local anaesthesia (lidocaine 1% with adrenaline 1:100,000, 3 to 5 mL). Success 95 to 99%.
  • Percutaneous release with an 18-gauge needle in the fingers (avoid in the thumb, where the digital nerve lies close).
  • Do not divide the A2 pulley (bowstringing).
  • Immediate finger motion, with return to light use in 1 to 2 weeks.
• Children: trigger thumb in infants often resolves spontaneously, so observe until about age 3. Splinting has limited benefit. A fixed flexion thumb that persists over age 3 is treated by A1 pulley release, with a very high success rate. Children's analgesia: paracetamol 15 mg/kg orally every 6 hours.
• Complications of surgery: digital nerve injury, bowstringing, incomplete release, infection, stiffness, scar tenderness and complex regional pain syndrome.

Follow up at 2 and 6 weeks after intervention. Counsel on recurrence (up to 30% after injection) and on glycaemic control.