Boutonniere Injury

A boutonniere deformity is flexion of the proximal interphalangeal joint and hyperextension of the distal interphalangeal joint of a finger, caused by disruption of the central slip of the extensor tendon at its insertion on the dorsal base of the middle phalanx. The lateral bands then slip volar to the axis of the joint and act as flexors of the proximal joint and extensors of the distal joint.

• Acute causes: a forced flexion of the extended proximal interphalangeal joint (a blow to the tip of a finger in a ball sport), volar dislocation of the joint, a dorsal laceration, burns and an avulsion fracture of the base of the middle phalanx. Chronic causes: rheumatoid arthritis (the commonest non-traumatic cause), psoriatic arthritis and Dupuytren disease.
• The deformity often does not appear for 1 to 3 weeks after the injury, because the triangular ligament holds the lateral bands dorsal at first, so the injury is commonly missed or labelled as a sprain.
• The long finger, ring finger and little finger are most often affected, and young active men and ball players are the commonest patients.

• Acute: swelling and tenderness over the dorsal proximal interphalangeal joint, pain, and loss of full active extension of the proximal joint (a lag of 10 to 30 degrees at first), with reduced ability to extend against resistance.
• Established: a finger with the proximal joint bent, the distal joint hyperextended (the "buttonhole" posture), and the nail facing a different direction, which becomes fixed over weeks to months.
• Elson test: the patient flexes the proximal interphalangeal joint to 90 degrees over a table edge and tries to extend it against resistance. Weak extension of the proximal joint with a rigid, extended distal joint (because the lateral bands are tight) indicates a central slip injury.
• Differential diagnosis: simple sprain, volar plate injury, proximal interphalangeal joint dislocation, mallet finger (distal joint flexion), swan neck deformity (the opposite posture), fracture of the middle phalanx base, pilon fracture, rheumatoid synovitis, trigger finger and Dupuytren contracture.
• Red flags: open wound, a displaced avulsion fracture, joint instability or subluxation, signs of infection, and rheumatoid disease.
• Complications: fixed deformity, stiff and painful finger, loss of grip, proximal interphalangeal arthritis and functional loss.

• Clinical. Examine every dorsal proximal interphalangeal injury as a possible central slip injury until proved otherwise. Test active extension, Elson test, joint stability and passive correction of the deformity.
• X-ray (anteroposterior, lateral and oblique) shows an avulsion fragment from the base of the middle phalanx, joint subluxation, and arthritis.
• Ultrasound can show the central slip disruption. MRI is used when uncertain. For open wounds, explore for tendon laceration.
• In chronic cases, check inflammatory markers and rheumatoid serology if there is polyarticular disease.

• Acute closed central slip injury (the main window is the first 2 to 6 weeks):
  • Splint the proximal interphalangeal joint in full extension (0 degrees) continuously, using a volar or dorsal splint or a cast, for 6 weeks, leaving the distal joint free. A loose joint extension should not be allowed even for hygiene. A pin through the joint is sometimes used.
  • The patient must keep the distal interphalangeal joint moving, with active and passive flexion, 20 to 30 times several times daily, which draws the lateral bands dorsally.
  • After 6 weeks, begin supervised active flexion, with night extension splinting for a further 2 to 4 weeks and a protective splint during sport for 4 to 6 weeks.
  • Pain: paracetamol 1 g orally 6 hourly, with ibuprofen 400 mg 8 hourly with food for 1 to 2 weeks if no contraindication.
• Open injuries and laceration: surgical exploration and repair of the central slip with suture, followed by splinting and a controlled mobilisation programme. Antibiotic cover (cefalexin 500 mg orally 6 hourly for 5 days) and tetanus review for contaminated wounds.
• Avulsion fracture: fixation if the fragment is displaced (above 2 mm), involves more than one third of the articular surface, or the joint is subluxed (screw, wire, or suture anchor).
• Established flexible deformity (after 6 weeks):
  • Serial casting or a dynamic extension splint (a spring or dynamic splint) for 6 to 8 weeks, then night splinting for 3 months.
  • Surgical options if conservative care fails and there is functional loss: central slip reconstruction with extensor tendon flaps, lateral band release (tenotomy of the terminal tendon over the middle phalanx, which restores distal flexion), and repair of the triangular ligament.
• Fixed deformity: capsular release and tendon reconstruction, proximal interphalangeal joint arthrodesis (in 20 to 40 degrees of flexion, depending on the digit) or arthroplasty, and amputation in a stiff, painful finger rarely.
• Rheumatoid arthritis: disease modifying drugs under rheumatology, splinting, and surgery for functional loss.
• Prognosis: acute injuries treated early with correct splinting recover in about 70 to 90%. Late treated or fixed deformities have poor outcomes with residual stiffness.
• Special groups:
  • Children: avulsion through the growth plate occurs, so X-ray carefully and refer.
  • Athletes: splint for sport and delay return to ball contact until 8 to 12 weeks.
  • Elderly: accept limited goals, and avoid prolonged immobilisation of other joints.
  • Pregnancy: splint and paracetamol. Avoid NSAIDs after 20 weeks.
  • Diabetes: watch for infection and stiffness.
• Follow up: review at 1 week to check splint fit, at 3 weeks, and at 6 weeks. Refer to hand surgery for any open injury, displaced avulsion, joint subluxation, a fixed or progressive deformity, or rheumatoid disease.