Mallet Finger

Extensor Apparatus

• Terminal Tendon: Formed by the confluence of the two lateral bands. Inserts into the dorsal lip of the distal phalanx.
• Central Slip: Inserts into the middle phalanx.
• Triangular Ligament: Prevents lateral bands from subluxing volarly.
• Oblique Retinacular Ligament (ORL): Links PIPJ extension to DIPJ extension.

The terminal tendon is wide and wafer thin (less than 1mm).

Swan Neck Mechanism

• Loss of distal anchor (Mallet) causes the extensor force to retract proximally.
• This increases tension on the Central Slip (hyperextending the PIPJ).
• If the Volar Plate at the PIPJ is lax, the PIPJ hyperextends.
• The Lateral Bands subluxate dorsally, locking the PIPJ in extension.
• Result: PIPJ Hyperextension + DIPJ Flexion.

This must be treated by correcting the DIPJ lag.

Blood Supply

• The dorsal skin of the DIPJ is supplied by tiny vascular branches.
• It is very susceptible to pressure necrosis from splints.
• Germinal Matrix: Lies immediately deep to the extensor tendon insertion. Nails are often damaged in Type IV injuries.

Care must be taken during K-wire insertion to avoid the germinal matrix.

Doyle Classification

• Type I: Closed tendinous injury. (Most common).
• Type II: Open injury (Laceration).
• Type III: Open injury with loss of skin/tendon substance.
• Type IV: Mallet Fracture.
  • IVa: Pediatric (Salter-Harris Physeal injury).
  • IVb: Adult, less than 30% articular surface.
  • IVc: Adult, greater than 30% articular surface / Subluxed.

Type IVc is the most debated category regarding surgical management.

Wehbe & Schneider

• Based on size of fragment and degree of subluxation.
• Rarely used clinically; the decision is binary (Stable vs Unstable).

Subluxation is the key determinant of instability.

Radiology

• Views: PA and True Lateral.
• Findings:
  • Avulsion: Triangular fragment from dorsal base of P3.
  • Subluxation: Volar subluxation of P3 relative to P2 head. (Surgical Indication).
  • Apposition: Gap between fragment and bone.

A "True Lateral" is essential to assess joint congruency.

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Conservative (Splinting)

• Indication: Type I, II, III, IVb (Stable).
• Protocol:
  • Initial: 6-8 weeks CONTINUOUS extension. (Reset clock if flexed).
  • Weaning: 2-4 weeks night splinting + sports/heavy use.
  • Type: Stack Splint (off the shelf) or Custom Thermoplastic.
• Outcome: 80-90% success. 5-10 degree lag is common but functional.

Patient education is the single most important factor in success.

Surgical Management

• Indication: Volar Subluxation, Large Fragment (greater than 30-50%), Open Injury, Failed Splinting (intolerant).
• Techniques:
  • Extension Block Pinning (Ishiguro): K-wire into P2 head blocks the fragment. P3 is extended to reduce it.
  • Open Reduction (ORIF): Screw/Hook plate. (High complication rate - comminution).
  • Tenodermodesis: For chronic tendon mallet (excise scar + plicate skin/tendon).

Surgical risks often outweigh the benefits for small fragments.

Ishiguro Extension Block Pinning

• Concept: Uses the P2 head as a backstop.
• Step 1: Flex DIPJ. Insert 1.0mm K-wire into distal P2 head, aimed dorsally.
• Step 2: Extend DIPJ. The fragment hits the wire and is reduced onto the P3 base.
• Step 3: Insert a second longitudinal K-wire across DIPJ to lock flexion.
• Pros: Percutaneous. No dissection.
• Cons: Pin track infection. Wire migration.

The blocking wire must be placed dorsal to the fracture fragment.

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Tenodermodesis (Brooks-Graner)

• Indication: Chronic tendinous mallet.
• Technique: Excise elliptical wedge of skin and tendon/scar from dorsal DIPJ.
• Repair: Close skin and tendon as one layer (Dermodesis).
• Splint: K-wire fixation for 6 weeks.

This salvage procedure sacrifices some DIPJ flexion for extension.

Outcomes by Treatment Type

Conservative Management (Splinting):

• Success Rate: 80-90% achieve good/excellent results
• Residual Lag: Average 5-10 degrees (functionally acceptable)
• Patient Satisfaction: High, especially with compliant patients
• Return to Work: 85% return to pre-injury occupation

Surgical Management:

• Success Rate: 70-80% (higher complication rate offsets benefits)
• Complications: Nail deformity (15%), infection (5-10%), stiffness (20%)
• Indication: Reserved for subluxed joints or failed splinting

Factors Affecting Outcome:

• Compliance: Single most important variable
• Delay to Treatment: Late presentation still responds to splinting
• Age: Younger patients heal faster, elderly have thinner skin (necrosis risk)
• Comorbidities: Diabetes, smoking impair tendon healing

Compliance is the single most important predictor of outcome.

Prognostic Factors

Key Prognostic Principles:

• Bony mallet heals better than tendinous (bone-to-bone vs tendon-to-bone)
• Persistent X-ray gap does NOT correlate with function - treat the patient, not the X-ray
• Swan Neck corrects when mallet is treated early

Remember: Treat the patient, not the X-ray.

Long-Term Outcomes

5-Year Follow-Up Data:

• Function: 90% full function (grip, pinch, dexterity)
• Pain: Rare - if present, suspect OA or Swan Neck
• Cosmesis: Minor droop (5-10 degrees) is common and accepted
• Re-injury: Low risk once healed; may need protective splint for contact sports

Return to Activity:

• Desk Work: 1-2 weeks (with splint)
• Manual Work: 8-12 weeks
• Non-Contact Sport: 10-12 weeks
• Contact Sport: 12-16 weeks (protective splinting recommended initially)

When to Refer Back:

• Progressive lag despite compliance
• Swan Neck development
• Persistent pain at 8-12 weeks
• Significant functional limitation

Most patients return to full function with minimal residual lag.