Mallet Finger — Management and Fixation

Definition and Mechanism

A mallet finger is a disruption of the terminal extensor tendon at its insertion on the dorsal base of the distal phalanx, at the DIP joint. The hallmark is loss of active DIP extension with preserved passive extension. The classic mechanism is a sudden forced flexion force applied to an actively extended fingertip — the ball-strike injury that gives it the nickname baseball finger. A direct blow to the dorsum of the DIP or a laceration can also produce it.

The lesion may be:

• Tendinous (soft-tissue) mallet — rupture of the terminal tendon itself
• Bony mallet — avulsion of a fragment of the dorsal base of the distal phalanx with the tendon still attached to it

Doyle Classification

Indications for Treatment

Non-operative (the mainstay)

• All closed soft-tissue (tendinous) mallets — Doyle Type I
• Most bony mallets, including those with a substantial fragment, provided the joint is congruent (no volar subluxation)
• Delayed presentation — even weeks to months old — still warrants a trial of continuous splinting

Operative indications (selective)

• A large bony fragment involving more than approximately one third of the articular surface WITH volar (palmar) subluxation of the distal phalanx — the subluxated, unstable joint is the real indication
• Open injuries — Doyle Types II and III (laceration or tissue loss)
• A subset of failures of a genuine, concordant trial of splinting
• Selected paediatric transepiphyseal fractures that are significantly displaced

Relative / cautious indications

• A fragment involving approximately one third or more of the surface WITHOUT subluxation is increasingly managed non-operatively, because the evidence shows fragment size alone does not dictate outcome
• Avoid operating simply for cosmesis of a dorsally prominent fragment

Evidence Base

• Cochrane systematic review: randomised trial evidence for treating mallet finger is limited and insufficient to determine the single best treatment; no trial has shown surgery to be superior to conservative splinting for the typical closed injury.
• Wehbe and Schneider (1984): in a landmark review of mallet fractures, the size of the fracture fragment did not correlate with the clinical result, supporting conservative management of most bony mallets.
• Crawford (1984): the molded polyethylene splint (the basis of the Stack-type splint) holds the DIP in extension while allowing skin care, improving patient concordance — the principle that underpins modern non-operative management.
• Operative series: extension-block (Ishiguro) pinning and ORIF are reported to give good reduction and outcome in bony mallets with volar subluxation, but they are reserved for the minority with an unstable joint.

The Extensor Mechanism over the Finger

The extensor tendon flattens over the dorsum of the finger into the extensor expansion (hood). At the level of the proximal phalanx it splits into a central slip (inserting on the base of the middle phalanx) and two lateral bands that pass distally on either side of the PIP.

The two lateral bands converge over the dorsum of the middle phalanx to form the terminal (extensor) tendon, which inserts on the dorsal base of the distal phalanx. It is the terminal tendon that is disrupted in a mallet finger.

Stabilising Ligaments of the Expansion

• Triangular ligament — transverse fibres linking the two lateral bands dorsally over the middle phalanx; keeps the bands from drifting volarly
• Transverse retinacular ligament — passes from the lateral bands volar to the PIP axis, anchoring the bands and limiting PIP hyperextension
• Oblique retinacular ligament (ORL) — runs from the flexor sheath at the proximal phalanx, passes volar to the PIP axis, and joins the terminal tendon; it links DIP extension to PIP extension (Landsmeer's linkage)

Extensor Tendon Zones (Doyle)

Why a Mallet becomes a Swan-Neck

When the terminal tendon fails, the DIP cannot extend and sits flexed. With the terminal insertion no longer tensioned, the lateral bands and the extensor force are redirected proximally to the central slip, driving the PIP into hyperextension. Loss of the check-rein effect of the oblique retinacular and transverse retinacular ligaments compounds this. The net result is the swan-neck posture: DIP flexion lag with PIP hyperextension. This is the classic late sequela of an untreated or chronic mallet.

The Distal Phalanx as a Fixation Target

The distal phalanx is small, with a thin dorsal cortex and the nail apparatus draped over its volar surface. This makes fixation demanding:

• Limited bone stock for screws or wires
• The germinal matrix of the nail lies volar to the dorsal base — at risk from dorsally placed hardware or a proximal incision
• The tuft is cancellous and does not hold fine hardware well

These constraints explain why percutaneous pinning (which needs only a small footprint of purchase) is often preferred over screw fixation, and why hardware problems dominate the complication list for this tiny bone.

Positioning and Preparation

Patient position: Supine with the hand resting on a radiolucent hand table. The forearm is pronated for a dorsal or midaxial approach to the DIP. Image intensifier is essential for any bony mallet fixation to confirm fragment reduction and joint congruity throughout.

Anaesthesia: Digital block or local infiltration (with or without epinephrine) is usually sufficient for percutaneous pinning; WALANT is well suited. Open fixation and open mallet repair may use a digital block or regional/general anaesthesia.

Consent: Specifically counsel on residual extension lag, swan-neck deformity, the risk of pin-tract infection and wire migration or breakage, nail deformity from nail-matrix injury, DIP stiffness and arthritis, and the prolonged splintage period.

A. Extension-Block (Ishiguro) Percutaneous Pinning

Indications

A closed bony mallet with volar subluxation of the distal phalanx, where the dorsal fragment is large enough to capture but the joint needs reduction. This is the most common operative technique for Doyle Type IVc.

Technique

1. Confirm the lesion: flex and extend the DIP under image; confirm the dorsal fragment and the volar subluxation of the distal phalanx on a true lateral view.
2. Flex the PIP to approximately 90 degrees. This positions the terminal tendon and dorsal fragment so that a block wire can control them.
3. Insert the block wire: pass a fine K-wire (typically 0.045 inch or 1.0 mm) percutaneously into the dorsal distal aspect of the head of the middle phalanx, angled distally at roughly 40 to 45 degrees. This wire acts as an extension block — it stops the dorsal fragment being driven dorsally and proximally when the DIP is extended.
4. Extend the DIP: as the distal phalanx is brought up into extension, the fragment is levered down against the block wire and the joint is reduced.
5. Confirm reduction: check the articular surface and the restoration of joint congruity on fluoroscopy.
6. Transfix the DIP: drive a second longitudinal K-wire from the tip of the distal phalanx across the DIP joint to hold full extension and maintain the reduction. Take care to avoid the nail matrix.
7. Finish: bend and cut the wires outside the skin, cap them, and protect the finger in a splint.

B. Open Reduction and Internal Fixation of a Large Fragment

Indications

A large, single, capturable dorsal fragment with volar subluxation where percutaneous methods cannot secure the reduction — for example a fragment too large or comminuted for Ishiguro pinning.

Technique

1. Approach: use a dorsal curvilinear (S-shaped) or lazy-S incision centred over the DIP, or a midaxial incision. Protect the nail matrix — if the incision extends proximal to the eponychial fold, elevate the germinal matrix carefully and avoid damaging it.
2. Expose the fracture: evacuate the haematoma and clear the fracture bed; identify the dorsal fragment still attached to the terminal tendon, and the dorsal base of the distal phalanx.
3. Reduce the fragment: bring the DIP into extension and anatomically reduce the fragment against the dorsal base. Hold it with a fine reduction clamp.
4. Fix the fragment — choose by fragment size and bone quality:
   • One or two 1.0 to 1.2 mm K-wires for a small or comminuted fragment
   • A small headless or mini-fragment lag screw for a single large fragment
   • A pull-out suture or wire (Bunnell tie-over) grasping the terminal tendon and exiting through the pulp, tied over a padded button, for a fragment too small for hardware
5. Protect the repair: add a longitudinal DIP transfixion K-wire for about six weeks to unload the fixation while the tendon and bone heal.
6. Closure and splintage: close the skin; apply a protective splint with the DIP extended and the PIP free.

C. Open (Laceration) Mallet Repair — Doyle Types II and III

Technique

1. Wound management: lavage and debride the wound; manage tetanus and antibiotic cover as for any open hand injury.
2. Assess the tendon ends: the terminal tendon is often retracted only a few millimetres; the skin laceration usually lies at the same level.
3. Repair the tendon: appose the tendon ends with a 4-0 or 5-0 non-absorbable suture using a modified Kessler or figure-of-eight configuration, taking care to avoid bulk that would limit skin closure.
4. Stabilise the DIP: pass a longitudinal K-wire across the DIP in full extension to protect the repair for about six weeks.
5. Skin closure and splintage: close the skin and apply a splint; begin active PIP motion from day one to prevent stiffness.

Splinting Protocol (Non-operative and Post-operative)

Continuous phase (first six to eight weeks)

• The DIP is held in slight hyperextension continuously, day and night, in a Stack, custom thermoplastic or aluminium-foam splint.
• The PIP is left free and is moved actively from day one.
• Skin care is performed with the DIP supported flat on a table so the tip never flexes — any flexion restarts the clock.

Weaning phase (next two to six weeks)

• Transition to night and activity splinting (for example during sport or heavy use).
• A graded wean: begin with short periods out of the splint while monitored, increasing the time as active extension is maintained.

After K-wire fixation

• The finger is protected in a splint with the DIP extended.
• The DIP transfixion wire (and block wire, if used) is removed at about six weeks under sterile technique.
• After wire removal, begin active DIP flexion and extension; buddy-tape for protection during the weaning phase.

Return to Function

• Desk and light activity: within days (splinted)
• Driving: once the patient has safe control of the splinted hand
• Manual work: around six weeks, once the joint is stable and any wires are out
• Contact sport: only with a protective splint in situ, typically after about eight weeks or once the fragment is stable

Hand Therapy Indications

• Residual extension lag at the end of continuous splinting — a further extension period
• PIP stiffness or a developing swan-neck posture — figure-of-eight or PIP-extension-control splinting
• Pin-site issues or wire-related discomfort — early review and pin care
• Chronic or neglected mallet — prolonged supervised splinting programme

Special Case: Chronic and Neglected Mallet

• Many mallet fingers present late, sometimes weeks to months after injury.
• A trial of continuous extension splinting for at least eight weeks is still worthwhile — a proportion will gain useful, even complete, extension even when treatment is delayed.
• If a residual lag and a swan-neck posture persist despite genuine concordant splinting, options include prolonged splinting, a figure-of-eight splint, or, for the symptomatic swan-neck, reconstructive surgery such as a superficialis tenodesis of the PIP.
• Counsel the patient that a small, functionally insignificant extension lag is an acceptable outcome and is often better than the risks of late surgery.

Special Case: Paediatric Mallet (Doyle Type IVa)

• In children the lesion is frequently a transepiphyseal fracture (a Salter-Harris pattern) rather than a tendon rupture, because the tendon is stronger than the physis.
• Manage with closed reduction and splinting if significantly displaced; take care to avoid crossing the growth plate with hardware where possible.
• Union and remodelling potential are excellent; counsel parents accordingly.