Boutonniere Deformity

Normal Extensor Anatomy (Zone III)

• Central Slip: Inserts into the dorsal base of the Middle Phalanx. Extends the PIPJ.
• Lateral Bands: Run laterally. Join distally to form Terminal Tendon.
• Triangular Ligament: Connects the two lateral bands dorsally over the Middle Phalanx. Prevents them falling volar.
• Transverse Retinacular Ligament: Connects lateral bands to the volar plate. Pulls them volar.

The interplay between the Triangular and Transverse ligaments is critical for stability.

Pathomechanics

1. Rupture: Central slip ruptures / avulses.
2. Loss of Extension: PIPJ extension is weakened (though lateral bands can still extend it weakly initially).
3. Ligament Failure: The Triangular Ligament attenuates or tears.
4. Subluxation: The Transverse Retinacular Ligament pulls the Lateral Bands volarly.
5. Axis Shift: Lateral bands drop below the axis of rotation of the PIPJ. They become PIPJ flexors.
6. Concentration: All extensor force is transmitted to the DIPJ leading to Hyperextension.

The lateral bands become shortening flexors of the PIPJ and heaving extensors of the DIPJ.

Burton Classification

• Stage I: Supple. Passive correction of PIPJ is possible.
• Stage II: Fixed deformity. Contracture of lateral bands.
• Stage III: Fixed deformity + Arthritis.

Stage I is treatable with splinting. Stage II requires surgical release or serial casting.

Nalebuff Classification (Rheumatoid)

Specifically addresses rheumatoid Boutonniere:

• Mild: PIPJ flexion lag less than 15°. Flexible deformity.
• Moderate: PIPJ flexion contracture 15-40°. Some limitation.
• Severe: PIPJ flexion contracture greater than 40°. Fixed deformity.

Important for RA patients where bilateral involvement is common and treatment goals differ from traumatic cases.

Etiologic Classification

• Traumatic:
  • Closed rupture (Zone III)
  • Open laceration
  • Bony avulsion of central slip insertion
• Inflammatory:
  • Rheumatoid arthritis (most common)
  • Psoriatic arthritis
  • SLE
• Post-Surgical:
  • After Swan neck reconstruction
  • After failed PIP arthroplasty

The etiology influences treatment choice and prognosis.

Examination

• Deformity: Look for PIP flexion and DIP hyperextension.
• Open: Check for dorsal laceration.
• Tenderness: Dorsal base of Middle Phalanx.
• Boyes Test: Test for tightness of oblique retinacular ligament.

Early changes can be subtle. Compare with the other hand.

Elson's Test

• Position: Place PIPJ in 90 degrees flexion over table edge.
• Action: Ask patient to extend finger against resistance.
• Normal: Central slip is tight. Patient feels significant power. DIPJ is loose (floppy) because lateral bands are slackened by PIP flexion.
• Rupture: Central slip is gone. Lateral bands are pulled tight to bypass the PIPJ. DIPJ becomes rigid/extended forcefully. Patient has weak PIP extension.

Key Finding: A rigid DIPJ during resisted PIP extension = Central Slip Rupture.

Radiology

• Views: AP and Lateral.
• Findings:
  • Avulsion: May see bony fleck from dorsal base of P2.
  • Joint: Assess for OA (Stage III).
  • Subluxation: Volar subluxation of middle phalanx may be visible.
  • Soft Tissue: Swelling dorsal to PIPJ.

Bony avulsion is treated similarly to tendinous rupture (Splinting), unless huge displaced fragment.

Ultrasound

• Role: Can visualise the integrity of the central slip dynamically.
• Findings: Discontinuity of the tendon fibers.
• Utility: Useful if exam is equivocal (swelling masking the slip).

Ultrasound is operator dependent.

MRI

• Role: Gold standard for soft tissue, but rarely needed.
• Indication: Diagnosis of equivocal cases in high demand athletes.
• Findings: Edema and disruption of the central slip insertion.
• Protocol: Axial and sagittal T2-weighted sequences show the central slip best.

MRI is expensive and usually unnecessary if clinical acumen is high.

Conservative Management (Stage I)

• Goal: Restore central slip continuity + Move lateral bands dorsal.
• Splint: PIPJ in FULL extension (block extension).
• DIPJ: LEFT FREE. Must be flexed actively.
• Mechanism: Active DIP flexion while PIP is extended pulls the lateral bands distally and dorsally (via Triangular ligament), reducing them.
• Duration: 6 weeks continuous.
• Follow-up: Weekly review to ensure compliance and splint fit.

This is known as the "Safety Splint" position.

Surgical Management

• Indication: Open injury, Bony avulsion (large), Failed splinting (Stage II/III).
• Techniques:
  • Direct Repair: For acute open injuries.
  • Reconstruction: Terminal tendon tenotomy (Fowler), Lateral band relocation (Littler), Central slip reconstruction (Matev).
  • Salvage: Arthrodesis (Fusion) for Stage III.
  • PIP Arthroplasty: Rarely indicated; reserved for rheumatoid patients.

Surgery is difficult because restoring the delicate balance of the extensor mechanism is hard.

Acute Repair

• Approach: Dorsal zig-zag incision centered over PIPJ.
• Repair: 4-0 non-absorbable mattress suture into central slip.
• Fixation: K-wire across PIPJ in extension for 3-4 weeks.
• Triangular Ligament: Must be repaired to prevent lateral band subluxation.
• Closure: Skin closure over buried sutures.

Do not overtighten the central slip, or you will cause a DIPJ extension lag. The goal is merely to appose the tendon ends, not to create tension.

Chronic Reconstruction

• Modified Littler: Isolate lateral bands, release them from volar tissues, sew them together dorsally over the P2.
• Fowler Tenotomy: Release the terminal tendon distally to increase slack in lateral bands, allowing them to shift dorsal and extend the PIPJ.
• Matev Reconstruction: Central slip reconstruction using a slip of the lateral band.
• Staged Approach: First release contracture, then reconstruct tendon.

Chronic reconstruction is notoriously unreliable. For Stage II (Fixed), release of the volar plate and check-rein ligaments is needed first. Serial casting may convert a Stage II to a Stage I, making reconstruction easier.