Mallet Finger

Patients present after a forced flexion injury (ball strike, stubbed finger, occupational trauma) with pain over the dorsal DIP and inability to actively extend the fingertip. The DIP rests in flexion, typically 20-45 degrees, depending on injury severity. Passive extension is usually preserved (the patient can extend the DIP by pushing it with the other hand) - this is the diagnostic discriminator from a fixed joint deformity.

Examination:

• •Inspect the resting DIP posture: characteristic flexion drop with extensor lag (the "mallet deformity")
• •Test active DIP extension against gravity (no resistance): clear loss is diagnostic. Quantify the extension lag in degrees
• •Test passive extension - usually full and free; document any restriction
• •Palpate the dorsal DIP for tenderness, soft-tissue swelling, and bony deformity. A palpable step suggests bony mallet
• •Check for open wounds (Doyle II/III) - these are usually operative even if tendinous
• •Document any associated PIP hyperextension (secondary swan-neck), especially in chronic / untreated cases

Differentials include central slip rupture (boutonniere deformity, with PIP flexion and DIP hyperextension), volar plate rupture of the DIP (rare; hyperextension mechanism), septic arthritis (warm tender DIP, systemic features), and felon (pulp space infection, fluctuant fingertip).

Plain radiographs (PA and TRUE LATERAL of the DIP joint, with the finger isolated to avoid overlap) are first-line and essential. The lateral view assesses for an avulsion fragment, fragment size as a percentage of articular surface, and any volar subluxation of the distal phalanx. Sub-optimal lateral views overlap fragments and miss subluxation - insist on a true lateral.

Key radiographic checks:

• •Presence of a bony fragment at the dorsal base of the distal phalanx
• •Fragment size as a percentage of the articular surface (Doyle IVB under 50%, IVC over 50%)
• •Volar subluxation of the distal phalanx (Doyle IVC)
• •Salter-Harris physeal injury in skeletally immature patients (Doyle IVA)

MRI and ultrasound are rarely indicated. Ultrasound can confirm tendinous mallet without a bony fragment, but the clinical picture (clear extensor lag with passive extension preserved and no fragment on X-ray) is usually sufficient. CT may be used in surgical planning for complex bony mallets but is not routine.

Routine bloods are not indicated. Document hand dominance, occupation, and sport for advice on splinting compliance.

Management is driven by injury type and Doyle subtype (BSSH guidance).

Closed tendinous mallet (Doyle I) and Doyle IVB (bony mallet under 50% articular surface, no volar subluxation): conservative.

• •Continuous DIP extension splinting for 6-8 weeks. UK options include the stack splint (commonest), thermoplastic custom splint (better fit, fewer skin issues), or aluminium foam splint. PIP must be free; only the DIP is splinted
• •Critical: the DIP must NOT flex even momentarily during splint changes for skin care. Splint compliance is the single largest determinant of outcome - a single flexion event resets the clock
• •After 6-8 weeks: gradual weaning over 2-4 weeks with daytime free, night splint continued. Resume normal activity at 10-12 weeks
• •Late presentations (within 8-12 weeks of injury) can still be managed conservatively with extension splinting, with somewhat reduced outcomes

Open mallet (Doyle II/III), bony mallet with over 50% articular surface or volar subluxation (Doyle IVC), paediatric Salter-Harris (Doyle IVA), failed conservative management: surgical referral.

• •Doyle II/III: tendon repair with or without primary skin closure
• •Doyle IVC: ORIF (typically extension-block K-wire fixation, with or without supplementary wire to reduce the fragment). The Ishiguro extension-block technique is the UK standard
• •Doyle IVA: surgical reduction of the physeal injury
• •Chronic mallet with persistent functional deformity: tenodermodesis (Brooks-Graner), spiral oblique retinacular ligament reconstruction, or DIP arthrodesis depending on patient demand and pattern

Missed or neglected mallet: even after weeks-to-months delay, a trial of extension splinting can produce useful improvement. Surgical reconstruction is the option for established mallet with significant functional impairment.

Referral pathway: all open injuries to ED / hand surgery same-day. Bony mallets with operative criteria to fracture clinic / hand surgery within 7-10 days. Closed tendinous mallets are managed in primary care or fracture clinic with structured splinting and hand-therapy review at 6-8 weeks.

Conservative pathway (tendinous mallet, Doyle IVB):

• •Weeks 0-6 (or 0-8): continuous DIP extension splinting. The PIP joint is left free and active PIP and MCP ROM is encouraged from day 1
• •Skin care: splint removed once daily for cleaning, with the DIP held in extension by the contralateral hand. A single moment of DIP flexion resets the splinting clock
• •Weeks 6-8: gradual weaning - daytime free, splint at night and during sport / risk activity for a further 2-4 weeks
• •Weeks 8-12: progressive DIP active and passive ROM, gentle resisted extension, and grip strengthening. Hand therapy referral is appropriate for failed self-management or stiffness
• •Return to non-contact sport: 8 weeks; contact sport: 10-12 weeks; manual work: 8-10 weeks depending on demand

Post-operative (ORIF of Doyle IVC):

• •Weeks 0-6: K-wire in situ with extension splinting; PIP and MCP ROM from day 1
• •Week 6: K-wire removal; commence gentle DIP ROM with continued night-time extension splinting
• •Weeks 6-12: progressive DIP ROM and strengthening
• •Return to sport: 10-12 weeks for non-contact, 12-16 weeks for contact

Expected outcomes:

• •Conservative management of tendinous mallet: 5-10 degree residual extensor lag is common and acceptable. Patients should be counselled accordingly
• •Operative management of Doyle IVC: extensor lag rare, but DIP stiffness and dorsal skin complications are recognised
• •Patient compliance with splinting is the single largest predictor of outcome

Persistent extensor lag over 30 degrees, swan-neck deformity, or functional impairment beyond 3 months should prompt referral for reconstructive options.

• •BSSH Mallet Finger Patient Information - UK hand-surgery framework: closed tendinous mallets and Doyle IVB managed in continuous extension splinting for 6-8 weeks; Doyle IVC and open injuries require surgical assessment.
• •Doyle classification (1993, refined 2003) - UK and international framework: Type I closed tendinous, Type II open tendinous, Type III open with skin loss, Type IV bony with subtypes IVA-IVC. Drives operative-vs-conservative decisions.
• •Handoll Cochrane Review (2004, updated) - No clear superiority of splint type (stack vs thermoplastic vs aluminium foam); compliance is the dominant outcome determinant.
• •Ishiguro et al. (1997) - Original description of extension-block K-wire fixation for Doyle IVC mallets. Persists as the standard UK operative technique.
• •BOA Standards for Trauma (BOASTs) - UK trauma standards covering hand injury principles, including time-critical aspects of open injuries and paediatric Salter-Harris pathways.

• •Doyle classification drives management. Doyle I (closed tendinous) and Doyle IVB (under 50% fragment, no subluxation) are conservative. Doyle IVC (over 50% fragment or volar subluxation) and Doyle II/III (open) are surgical.
• •A TRUE LATERAL of the DIP joint is essential - it determines fragment size and detects volar subluxation. Poor laterals miss Doyle IVC.
• •Splint compliance is the single largest determinant of outcome. The DIP must not flex even briefly during splint changes; a single flexion event resets the splinting clock.
• •Mallet finger left untreated can develop a secondary swan-neck deformity from compensatory PIP hyperextension. Counsel patients and stress compliance.
• •Late presentations (within 8-12 weeks of injury) can still benefit from extension splinting. Don't discount conservative management just because the patient presents late.
• •Stack splint, thermoplastic custom splint, and aluminium foam splint all give equivalent outcomes if compliance is good. Patient choice and fit matter more than splint type.