INTRODUCTION TO LESSER TOE DEFORMITIES
Lesser toe deformities are among the most common pathologies encountered in foot and ankle surgery, frequently presenting as a combination of sagittal and axial plane malalignments. While sagittal plane deformities (such as hammer toes, claw toes, and mallet toes) are widely recognized and treated with interphalangeal joint arthroplasty or arthrodesis, residual axial plane deformities—specifically varus or valgus deviation of the digit—often require targeted osseous correction.
For residual deformity in the axial plane, an osteotomy at the proximal metaphysis of the proximal phalanx provides powerful and reliable realignment. By altering the mechanical axis of the digit at its base, surgeons can correct complex multiplanar deformities that soft tissue balancing alone cannot resolve. This masterclass details the pathoanatomy of lesser toe deformities, differentiates between hammer and claw toe etiologies, and provides a comprehensive, step-by-step guide to the closing wedge osteotomy of the proximal phalanx, highlighting the renowned Kilmartin and Kane technique.
PATHOANATOMY AND BIOMECHANICS
To effectively correct lesser toe deformities, the orthopedic surgeon must possess a profound understanding of forefoot biomechanics. The stability and alignment of the lesser toes depend on a delicate equilibrium between the extrinsic musculature (extensor digitorum longus [EDL], flexor digitorum longus [FDL], and flexor digitorum brevis [FDB]) and the intrinsic musculature (lumbricals and interossei).
The Intrinsic-Extrinsic Balance
The intrinsic muscles of the foot, specifically the interossei and lumbricals, pass plantar to the transverse metatarsal ligament and the axis of rotation of the metatarsophalangeal (MTP) joint, but dorsal to the axis of rotation of the proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints.
* Normal Function: They act to flex the MTP joint and extend the PIP and DIP joints.
* Pathologic State: When intrinsic function is compromised (the "intrinsic-minus" foot), the extrinsic extensors (EDL) overpower the MTP joint, driving it into hyperextension. Concurrently, the extrinsic flexors (FDL, FDB) overpower the interphalangeal joints, driving them into flexion.
Clinical Pearl: The Kelikian push-up test is essential during clinical evaluation. By applying upward pressure on the plantar aspect of the metatarsal head, the surgeon can determine if the MTP and PIP deformities are flexible (passively correctable) or fixed. Fixed deformities require osseous resection or osteotomy, whereas flexible deformities may be managed with soft tissue transfers (e.g., Girdlestone-Taylor procedure).
DIFFERENTIATING HAMMER TOE AND CLAW TOE DEFORMITIES
While often used interchangeably by novices, "hammer toe" and "claw toe" represent distinct clinical entities with different etiologies, pathoanatomies, and treatment algorithms.
Hammer Toe Deformity
A hammer toe is primarily a sagittal plane deformity characterized by abnormal flexion at the PIP joint.
* Joint Involvement: The flexion deformity at the PIP joint may be fixed (not passively correctable to neutral) or flexible. The DIP joint usually remains supple but may develop a compensatory extension or flexion deformity.
* MTP Joint Status: If the PIP flexion contracture is severe and chronic, the MTP joint may secondarily deform into extension. However, MTP extension is not an obligatory finding in early hammer toes.
* Distribution: Typically involves only one or two digits (most commonly the second toe, especially in the presence of a hallux valgus deformity that causes mechanical crowding).
* Etiology: Usually mechanical, related to ill-fitting footwear, a long second ray, or secondary to hallux valgus (crossover toe deformity).
Claw Toe Deformity
A claw toe is a complex, multi-joint deformity that is highly indicative of an underlying systemic or neurologic abnormality.
* Joint Involvement: Characterized by obligatory hyperextension at the MTP joint, combined with flexion deformities at both the PIP and DIP joints.
* Distribution: Frequently involves all the lesser toes simultaneously.
* Etiology: Claw toes are classically caused by neuromuscular diseases that lead to intrinsic muscle wasting. Conditions such as Charcot-Marie-Tooth disease, diabetic peripheral neuropathy, poliomyelitis, and spinal dysraphism must be ruled out. The loss of intrinsic muscle stabilization allows the extrinsic muscles to dictate the position of the digit, resulting in the classic clawed appearance.
Surgical Warning: Performing isolated PIP arthroplasties on a patient with true claw toes without addressing the hyperextended MTP joints and the underlying neuromuscular imbalance will inevitably lead to catastrophic recurrence and patient dissatisfaction.
INDICATIONS FOR PROXIMAL PHALANX CLOSING WEDGE OSTEOTOMY
The closing wedge osteotomy of the proximal phalanx is specifically indicated for:
1. Residual Axial Deformity: Varus or valgus malalignment of the toe that persists after MTP joint release and PIP joint correction.
2. Crossover Toe Deformity: As an adjunct to lateral collateral ligament reconstruction and medial capsular release at the MTP joint.
3. Congenital Curly Toe: In pediatric or young adult patients where the deformity is rigid and causes painful keratotic lesions.
4. Post-Traumatic Malunion: Following fractures of the proximal phalanx that have healed in angular deformity.
Contraindications
- Active infection (local or systemic).
- Severe peripheral vascular disease (inadequate perfusion to heal the osteotomy or survive the surgical insult).
- Inadequate bone stock (severe osteopenia or cystic changes at the metaphyseal base).
- Purely flexible deformities that can be corrected with soft tissue balancing alone.
PREOPERATIVE PLANNING
Thorough preoperative planning is mandatory. Weight-bearing anteroposterior (AP), lateral, and oblique radiographs of the foot must be obtained.
* Radiographic Assessment: Evaluate the MTP joint for subluxation or dislocation. Assess the length of the metatarsals (a long second metatarsal may require a concurrent Weil osteotomy). Measure the degree of varus or valgus angulation at the proximal phalanx to determine the size of the wedge to be resected.
* Vascular Assessment: Palpate dorsalis pedis and posterior tibial pulses. If pulses are diminished, non-invasive vascular studies (Ankle-Brachial Index, toe pressures) are required before proceeding with forefoot surgery.
SURGICAL TECHNIQUE: CLOSING WEDGE OSTEOTOMY (KILMARTIN AND KANE)
The technique described by Kilmartin and Kane is the gold standard for addressing axial deviations of the proximal phalanx. It utilizes a metaphyseal osteotomy, which benefits from the robust healing potential of cancellous bone, and employs a "greenstick" fracture technique to maintain inherent stability.
1. Anesthesia and Positioning
- The procedure is typically performed under regional anesthesia (ankle block or popliteal block) with intravenous sedation, or general anesthesia depending on patient preference and concurrent procedures.
- The patient is positioned supine on the operating table. A bump may be placed under the ipsilateral hip to internally rotate the leg to a neutral position.
- A calf or ankle tourniquet is applied and inflated to 250 mm Hg after exsanguination with an Esmarch bandage to ensure a bloodless surgical field.
2. Incision and Dissection
- Make a 3-cm "lazy-S" incision over the dorsal aspect of the proximal phalanx. The incision should extend from the midpoint of the proximal phalanx medially, curving proximally toward the MTP joint.
- Rationale for Lazy-S: A straight longitudinal incision over the joint can lead to dorsal scar contracture, exacerbating MTP extension. The lazy-S mitigates this risk.
- Deepen the incision directly to the bone. The dissection must pass medial and plantar to the extensor tendon apparatus, carefully retracting it laterally to avoid iatrogenic injury.
- Identify and protect the dorsal neurovascular bundles, which run along the medial and lateral borders of the digit.
3. Capsular Exposure
- Divide the periosteum and joint capsule to expose the base of the proximal phalanx only.
- Crucial Step: Do not extend the capsular incision proximally onto the metatarsophalangeal joint unless a concurrent MTP release is planned. Preserving the MTP capsule maintains the stability of the joint and prevents iatrogenic subluxation.
4. Executing the Osteotomy
The goal is to remove a medially or laterally based wedge of bone (depending on the deformity) at the metaphyseal flare. For a toe in varus, a lateral closing wedge is performed; for a toe in valgus, a medial closing wedge is performed.
- Identify the metaphyseal-diaphyseal junction, where the flare of the base of the phalanx meets the tubular shaft.
- Instrumentation: While a microsagittal saw can be used, many master surgeons prefer a 2-mm or 3-mm high-speed burr. The burr allows for precise, controlled bone removal without the risk of the saw blade skipping or causing thermal necrosis if irrigated properly.
- The First Cut: Make the first osteotomy cut parallel with the articular base of the phalanx. Pass the burr or saw through the dorsal, plantar, and medial cortices.
- Preserving the Hinge: It is imperative to leave the contralateral cortex (e.g., the lateral cortex for a medial closing wedge) intact. This intact cortex acts as a tension band and hinge, providing immense inherent stability to the osteotomy.
- The Second Cut: Make the second, more distal cut. This cut should be parallel with the distal end of the toe (perpendicular to the deviated shaft). Ensure that this distal cut converges with the proximal cut at the intact cortex, creating a perfect wedge (see Fig. 83-11 in standard texts).
Surgical Pitfall: Over-resection of the wedge will lead to overcorrection and a secondary deformity in the opposite direction. It is safer to resect a conservative wedge, assess the alignment, and remove more bone if necessary. If the hinge cortex is inadvertently breached, the osteotomy becomes infinitely more unstable and will require rigid internal fixation.
5. Closure and Fixation
- Gently manipulate the toe to close the osteotomy gap. The intact cortex should bend, creating a "greenstick" fracture that perfectly apposes the cancellous surfaces of the wedge.
- Fixation: While the greenstick osteotomy is inherently stable, internal fixation is highly recommended to prevent displacement during the healing phase.
- Fixation is typically achieved using a 0.045-inch or 0.062-inch Kirschner wire (K-wire).
- If a concurrent PIP joint resection arthroplasty is being performed for a hammer toe, the same K-wire used to stabilize the PIP joint can be driven proximally across the basilar osteotomy and into the metatarsal head.
- Drive the K-wire axially from the tip of the toe, across the DIP and PIP joints, across the closed osteotomy site, and into the base of the proximal phalanx. Depending on MTP stability, the wire may be advanced across the MTP joint into the metatarsal.
6. Wound Closure
- Deflate the tourniquet and achieve meticulous hemostasis.
- Irrigate the wound copiously with sterile saline.
- Close the periosteum and subcutaneous tissues with 4-0 absorbable sutures (e.g., Vicryl).
- Close the skin with 4-0 or 5-0 non-absorbable monofilament sutures (e.g., Nylon) using a horizontal mattress or simple interrupted technique.
- Apply a sterile, non-adherent dressing, followed by a compressive forefoot wrap. The toe should be splinted in the corrected position using the dressing.
POSTOPERATIVE PROTOCOL
The success of a proximal phalanx osteotomy relies heavily on strict adherence to postoperative protocols.
- Weight-Bearing Status: Patients are typically allowed heel-weight bearing or flat-foot weight bearing in a rigid, postoperative shoe immediately following surgery. Forefoot loading and toe-off must be strictly avoided.
- Pin Care: If the K-wire protrudes through the skin at the tip of the toe, pin site care is initiated at the first postoperative visit (usually 10-14 days). The pin is protected with a pin cap to prevent snagging.
- Suture Removal: Skin sutures are removed at 14 to 21 days, provided the incision is fully healed.
- Pin Removal: The K-wire is typically removed in the clinic at 4 to 6 weeks postoperatively, once clinical and radiographic evidence of osteotomy consolidation is observed.
- Rehabilitation: Following pin removal, patients are transitioned to a wide-toe-box shoe. Active and passive range of motion exercises for the MTP and DIP joints are initiated to prevent debilitating stiffness.
COMPLICATIONS AND MANAGEMENT
While generally safe and highly effective, the closing wedge osteotomy of the proximal phalanx carries specific risks that the surgeon must be prepared to manage.
1. Vascular Compromise ("White Toe")
The most feared complication in lesser toe surgery is vascular compromise. If the toe appears blanched and capillary refill is absent after tourniquet deflation and deformity correction, immediate action is required.
* Management: Remove all restrictive dressings. Place the foot in a dependent position. Apply warm saline compresses. If the toe remains ischemic, the K-wire must be removed, and the toe allowed to return to a slightly deformed position to relieve tension on the neurovascular bundles. Papaverine or topical nitroglycerin may be applied to relieve vasospasm.
2. Nonunion and Delayed Union
Because the osteotomy is performed in the well-vascularized metaphyseal bone, nonunion is rare, especially if the greenstick hinge is preserved.
* Management: If delayed union occurs, prolonged immobilization in a rigid shoe is usually sufficient. True nonunion may require revision surgery with bone grafting and rigid internal fixation (e.g., mini-fragment plates or screws).
3. Malunion and Recurrence
Malunion typically results from inaccurate wedge resection or failure of fixation. Recurrence of the deformity is often due to failure to address the underlying soft tissue imbalances (e.g., unaddressed MTP subluxation or intrinsic minus foot).
* Management: Mild malunions are often asymptomatic and require only shoe modification. Severe, painful malunions require revision osteotomy.
4. Pin Tract Infection
Superficial pin tract infections are common with percutaneous K-wires.
* Management: Most resolve rapidly with a short course of oral antibiotics (e.g., Cephalexin) and enhanced local pin care. Deep infections tracking to the bone require immediate pin removal and potentially surgical debridement.
CONCLUSION
The closing wedge osteotomy of the proximal phalanx is an indispensable technique in the armamentarium of the foot and ankle surgeon. By mastering the Kilmartin and Kane technique, understanding the critical differences between hammer and claw toe pathoanatomy, and executing precise osseous and soft-tissue balancing, surgeons can reliably restore the biomechanical axis of the lesser toes, alleviating pain and preventing long-term recurrence.
