INTRODUCTION AND PATHOANATOMY

The mallet finger deformity, characterized by an inability to actively extend the distal interphalangeal joint (DIPJ), is the most common closed tendon injury of the hand. While acute injuries are highly amenable to conservative management via strict immobilization, the chronic mallet finger presents a significantly more complex reconstructive challenge.

Chronicity in the context of a mallet finger is generally defined as an injury presenting or persisting beyond 4 to 12 weeks. The raw text from Hutaifortho's Operative Orthopaedics emphasizes that a mallet finger caused by the avulsion of the extensor tendon from the distal phalanx can often be satisfactorily treated by splinting even 12 weeks after the initial injury. Prolonged splinting—sometimes extending well beyond the standard 6 to 8 weeks—may yield successful outcomes, though the duration is frequently limited by patient compliance and tolerance of the orthosis.

When conservative measures fail, or when a patient presents late with a severe extensor lag but preserved passive DIPJ extension, secondary surgical repair is indicated. The pathoanatomy of a chronic mallet finger involves the interposition of disorganized, non-functional scar tissue between the retracted proximal terminal extensor tendon and its insertion at the dorsal base of the distal phalanx. Over time, this attenuation leads to a biomechanical imbalance. The proximal retraction of the extensor mechanism concentrates extension forces at the proximal interphalangeal joint (PIPJ), which, if left untreated, can stretch the volar plate and precipitate a secondary swan neck deformity.

CLINICAL EVALUATION AND INDICATIONS

Thorough preoperative evaluation is paramount to determining the appropriate surgical candidate for a secondary mallet repair.

Clinical Assessment

1. Extensor Lag: Measure the degree of active extension deficit at the DIPJ using a goniometer. A droop of greater than 30 to 40 degrees is typically functionally limiting and cosmetically displeasing.
2. Passive Range of Motion (ROM): Crucial Step. The examiner must passively extend the DIPJ. Secondary soft-tissue repair is only indicated if full, or near-full, passive extension is achievable. If the joint is fixed in flexion (contracture), a soft-tissue reconstruction will fail, and the patient will require either a preliminary serial casting/splinting protocol to regain passive extension or a salvage procedure such as DIPJ arthrodesis.
3. Swan Neck Deformity: Assess the PIPJ for hyperextension. A flexible swan neck deformity may resolve once the terminal tendon is repaired and tension is restored to the distal mechanism.

Radiographic Evaluation

Standard posteroanterior (PA), true lateral, and oblique radiographs of the affected digit are mandatory.
* Rule out arthritis: Degenerative joint disease at the DIPJ is a contraindication to soft-tissue repair.
* Assess for subluxation: Ensure the distal phalanx is concentrically reduced.
* Identify bony fragments: While this guide focuses on tendinous avulsions, chronic bony mallet injuries with large intra-articular fragments may require different reconstructive strategies.

Indications for Secondary Repair

• Failure of a strict, prolonged splinting regimen (up to and exceeding 12 weeks).
• Severe, functionally limiting DIPJ droop.
• Preserved passive extension of the DIPJ.
• Absence of advanced osteoarthritis at the DIPJ.
• A motivated patient capable of adhering to a strict postoperative rehabilitation protocol.

⚠️ Surgical Warning: Patient Selection

Do not attempt a secondary soft-tissue repair on a stiff, contracted DIPJ. The reconstructed tendon will not have the power to overcome a fixed volar capsular contracture, leading to immediate recurrence of the lag and surgical failure. Arthrodesis is the procedure of choice for the stiff, chronic mallet finger.

PREOPERATIVE PLANNING AND ANESTHESIA

Anesthesia Options

Secondary repair can be performed under various anesthetic modalities:
* Wide Awake Local Anesthesia No Tourniquet (WALANT): Utilizing a mixture of lidocaine and epinephrine allows for intraoperative assessment of tendon tension and active ROM. This is increasingly becoming the gold standard for extensor tendon surgery.
* Regional Block: A digital or wrist block with a forearm or finger tourniquet is a traditional and highly effective alternative.
* General Anesthesia: Rarely indicated unless the patient is highly anxious or multiple complex procedures are being performed simultaneously.

Equipment Required

• Loupe magnification (2.5x to 3.5x).
• 0.045-inch Kirschner wires (K-wires) and a wire driver.
• Fine tenotomy scissors and delicate tissue forceps.
• 4-0 monofilament nylon or wire for the tendon repair.
• 5-0 monofilament nylon for skin closure.
• Small metal or thermoplastic splints for postoperative immobilization.

SURGICAL TECHNIQUE: STEP-BY-STEP MASTERCLASS

The goal of secondary repair is to excise the non-functional intercalated scar tissue, advance the healthy proximal tendon, and secure it to the distal stump or bone under appropriate tension, protected by temporary transarticular fixation.

1. Incision and Exposure

Precision in the surgical approach is critical to avoid devascularizing the delicate dorsal skin flap and to prevent iatrogenic injury to the nail matrix.

• Incision Design: Make a small V-shaped or U-shaped incision over the dorsum of the DIPJ. The convexity of the incision should face distally.
• Landmarks: The distal tip of the V or U must be no closer than 5 mm proximal to the nail base (eponychial fold).
• Rationale: This 5 mm buffer is absolute. Violating this space risks irreversible injury to the germinal matrix, which will result in permanent, cosmetically devastating nail deformities (e.g., ridging, split nail).

💡 Clinical Pearl: Flap Elevation

The dorsal skin over the DIPJ is exceptionally thin and relies on a fragile subdermal plexus. When elevating the V- or U-shaped flap, use skin hooks rather than forceps to minimize crush injury to the edges.

2. Dissection and Flap Elevation

• Develop the flap gently in the plane directly between the extensor tendon mechanism and the subcutaneous fat.
• Elevate the flap proximally to fully expose the terminal extensor tendon, the DIPJ capsule, and the intervening pseudotendon (scar tissue).
• Maintain meticulous hemostasis using bipolar electrocautery to avoid thermal necrosis of the skin flap or the tendon.

3. Tendon Preparation and Scar Resection

In a chronic mallet finger, the gap between the retracted tendon and its insertion is bridged by an attenuated, disorganized scar.

• Identification: Carefully trace the terminal tendon distally until you identify the junction where normal, organized tendinous fibers transition into amorphous scar tissue.
• Transection: Sever the tendon transversely just proximal to the joint line, at the junction of healthy tendon and scar.
• Distal Stump: Leave the distal insertion of the tendon (or scar) attached to the dorsal base of the distal phalanx. This provides a robust anchor for the subsequent repair.
• Resection: Resect a sufficient amount of the intervening scar and attenuated tendon. The exact amount resected is determined by the tension required to close the gap when the finger is held in maximal hyperextension.

⚠️ Surgical Warning: Over-Tensioning

While resecting scar tissue is necessary, avoid excessive shortening of the extensor mechanism. Over-tensioning the terminal tendon can severely restrict DIPJ flexion and may inadvertently limit PIPJ flexion due to the interconnected nature of the extensor hood.

4. Transarticular Joint Fixation

To protect the delicate tendon repair from the massive mechanical advantage of the flexor digitorum profundus (FDP), the DIPJ must be rigidly immobilized.

• Positioning: Manually reduce the DIPJ into neutral or slight hyperextension (0 to 5 degrees). Avoid extreme hyperextension, which can cause dorsal skin blanching and subsequent necrosis.
• K-wire Insertion: Drive a 0.045-inch K-wire longitudinally across the DIPJ.
• Technique: The wire can be introduced antegrade through the distal phalanx (starting just volar to the nail bed) and driven proximally across the joint into the middle phalanx. Ensure the wire engages the subchondral bone of the middle phalanx for rigid stability.
• Verify the position of the K-wire with intraoperative fluoroscopy to ensure it is centrally located and does not violate the PIPJ. Cut the pin outside the skin and bend it to prevent migration.

5. Tendon Repair (Surgical Technique 66-22)

With the joint securely pinned in extension, the tendon ends will approximate with minimal tension.

• Suture Selection: Utilize a 4-0 monofilament nylon or a 4-0 monofilament wire.
• Pull-out Roll Stitch: Execute a pull-out roll stitch (often referred to as a Bunnell or modified Kessler pull-out technique). Pass the suture through the proximal healthy tendon, cross the joint line, and secure it to the distal stump/insertion site. The pull-out technique allows the suture to be removed later, minimizing retained foreign bodies directly under the thin dorsal skin.
• Alternative - Dermotenodermal Suture: As an alternative to a formal tendon weave, a dermotenodermal suture technique (tenodermodesis) can be employed. This involves passing a 4-0 nylon suture through the skin, the proximal tendon, the distal tendon stump, and back out through the skin. This effectively plicates the skin, tendon, and capsule as a single unit.
• Simplicity: As noted in standard operative texts, no additional core or epitendinous sutures are required. The transarticular K-wire provides the primary mechanical stability; the suture merely maintains tissue apposition during biologic healing.

6. Closure and Dressing

• Skin Closure: Close the V- or U-shaped skin flap with interrupted 5-0 monofilament nylon sutures. Ensure the skin edges are perfectly everted and not under excessive tension. If the skin blanches upon tying the sutures, the joint may be hyperextended too far, or too much tissue was resected.
• Dressing: Apply a non-adherent dressing (e.g., Xeroform or Adaptic) over the incision and the pin site.
• Immobilization: Maintain the finger in extension and apply a sterile compressive dressing. Support the entire digit with a volar splint (aluminum foam or custom thermoplastic) for postoperative comfort and to absolutely avoid reinjury or accidental pin bending during the immediate recovery period.

POSTOPERATIVE CARE AND REHABILITATION

The success of a secondary mallet finger repair relies as much on the rigorous postoperative rehabilitation protocol as it does on the surgical execution. The healing tendon is exceptionally vulnerable to stretching for several months.

Phase 1: Immediate Postoperative Period (Weeks 0 to 2)

• The patient remains in the initial surgical dressing and volar splint.
• Elevation and strict edema control are emphasized.
• Suture Removal: The skin sutures are removed at 10 to 14 days postoperatively.
• The transarticular 0.045-inch K-wire is left in place and protected by a small, custom-fitted metal or thermoplastic splint.

Phase 2: Intermediate Protection (Weeks 2 to 6)

• The DIPJ is maintained in strict extension by the K-wire.
• Pin site care is performed daily (e.g., cleaning with chlorhexidine or half-strength hydrogen peroxide) to prevent superficial tracking infections.
• Active ROM of the metacarpophalangeal (MCP) and PIP joints is encouraged to prevent stiffness in the rest of the digit.
• K-wire Removal: The transarticular K-wire is removed in the clinic at 4 to 6 weeks postoperatively. This is typically done without anesthesia.

Phase 3: Splinting and Weaning (Weeks 6 to 8+)

• Following K-wire removal, the tendon repair remains fragile. The DIPJ must be protected with a splint for a total of 8 weeks from the date of surgery.
• After 8 weeks, the patient may begin gentle, active flexion of the DIPJ.
• Weaning: The splint is gradually weaned during the day but must be worn continuously at night and during high-risk activities for an additional 2 to 4 weeks.
• If any extensor lag begins to recur during the weaning phase, the patient must immediately revert to full-time splinting for an additional 2 to 3 weeks.
• Normal activities, including heavy gripping and sports, are progressively resumed only after 10 to 12 weeks, provided there is no recurrent lag.

COMPLICATIONS AND PITFALLS

Surgeons undertaking secondary repair of chronic mallet fingers must be prepared to manage several potential complications:

1. Skin Necrosis: The most devastating early complication. Caused by overly aggressive flap elevation, excessive joint hyperextension, or tight skin closure. Prevention: Respect the subdermal plexus, use skin hooks, and pin the joint in neutral, not extreme hyperextension.
2. Nail Matrix Deformity: Caused by placing the incision too far distally. Prevention: Strictly adhere to the rule of keeping the incision at least 5 mm proximal to the eponychial fold.
3. Pin Tract Infection: Common with exposed K-wires. Management: Oral antibiotics and local pin care. If deep infection or osteomyelitis is suspected, the pin must be removed prematurely, and the patient placed in a strict external splint.
4. Recurrent Extensor Lag: Often due to premature K-wire removal, patient non-compliance with the splinting protocol, or failure to resect adequate scar tissue intraoperatively. Management: Reinstitute strict splinting. If it fails, arthrodesis is the salvage pathway.
5. DIPJ Stiffness: A mild loss of terminal flexion is an expected and acceptable trade-off for correcting the extensor lag. Severe stiffness, however, can impair grip. Prevention: Avoid over-tensioning the tendon repair and encourage early PIPJ/MCPJ motion.

CONCLUSION

The secondary repair of a chronic mallet finger is a highly precise surgical intervention reserved for patients who have failed exhaustive conservative management and present with a severe, flexible extensor lag. By meticulously resecting the intercalated scar, advancing the healthy tendon, and providing rigid transarticular K-wire fixation, the surgeon can restore the biomechanical integrity of the terminal extensor mechanism. Strict adherence to the 8-week postoperative immobilization protocol is the final, non-negotiable requirement for achieving a successful, durable clinical outcome.