Boutonniere Deformity

Boutonniere deformity is flexion of the proximal interphalangeal joint with hyperextension of the distal interphalangeal joint, caused by rupture or attenuation of the central slip of the extensor tendon at the base of the middle phalanx.

With the central slip gone, the lateral bands migrate volar to the axis of the proximal joint and become flexors of that joint, while their tension on the terminal tendon hyperextends the distal joint.

The triangular ligament stretches over 1 to 3 weeks, so the deformity often develops late and the injury is easily missed.

Causes:

• Closed trauma (forced flexion of an extended proximal joint, or a volar dislocation)
• Open laceration and burns
• Inflammatory arthritis, especially rheumatoid arthritis

Stages: I supple and passively correctable, II fixed contracture, III fixed with joint surface destruction. Delayed treatment leads to fixed contracture, proximal joint arthritis and loss of grip. Complications are stiffness, recurrent deformity and cartilage damage.

• Pain and swelling over the dorsum of the proximal interphalangeal joint, with tenderness at the base of the middle phalanx
• Early: weakness of proximal joint extension with a lag of 10 to 30 degrees
• Elson test: the proximal joint is flexed to 90 degrees over the edge of a table, and resisted extension of the middle phalanx produces a rigid distal joint (tight lateral bands) and no proximal extension force if the central slip is torn
• Established: fixed flexion of the proximal joint with hyperextension of the distal joint
• Red flags: open wound, volar dislocation, infection, rheumatoid synovitis and a missed injury after a finger "jam"

• Clinical diagnosis: passive correctability, the Elson test, and the active extension lag.
• Radiographs (true lateral): avulsion fracture of the dorsal base of the middle phalanx, joint subluxation and arthritis.
• Ultrasound or MRI for central slip continuity when the diagnosis is uncertain.

Differentials: mallet finger, swan neck deformity, proximal interphalangeal dislocation, volar plate injury, osteoarthritis, rheumatoid arthritis, Dupuytren contracture, trigger finger.

Acute closed injury or supple deformity:

• Continuous splinting of the proximal interphalangeal joint in full extension for 6 weeks (a volar or dorsal splint, with the distal joint free), with active distal joint flexion exercises 3 times daily to retrain the lateral bands.
• Then part time splinting and night splinting for 4 to 6 weeks.
• Alternatively, a transarticular 1.1 mm Kirschner wire across the proximal joint for 6 weeks.
• Paracetamol 1 g orally every 6 hours and ibuprofen 400 mg orally every 8 hours with food for up to 7 days.

Surgery:

• Open laceration: repair of the central slip with 4-0 non-absorbable suture or an anchor, and protective pinning.
• Displaced avulsion fracture (over 2 mm step or over 30% of the articular surface): open reduction with a mini screw or suture anchor.
• Chronic supple deformity: central slip reconstruction (for example, a lateral band transfer), with terminal tendon tenotomy to rebalance a hyperextended distal joint.
• Fixed contracture: serial casting or dynamic extension splinting over 3 to 6 months, then release of the volar plate and lateral band mobilisation if splinting fails.
• Joint destruction: arthrodesis in 30 to 40 degrees of flexion or arthroplasty.
• Cefazolin 2 g IV before incision (3 g if over 120 kg).

Rheumatoid deformity: control synovitis with methotrexate 7.5 to 25 mg orally once weekly with folic acid 5 mg orally once weekly (on a different day), monitoring blood count, liver enzymes and creatinine every 2 to 4 weeks at first. Add surgery when function is lost.

Complications: stiffness, recurrent deformity, pin tract infection, joint arthritis and loss of motion.

Follow up weekly for 2 weeks, then at 6 and 12 weeks. Counsel on strict adherence to splinting and early treatment of finger jams.