Operative Management of Tarsal Malunions: A Comprehensive Surgical Guide

Introduction to Tarsal Malunions

Malunion of the lesser tarsal bones—specifically the navicular, cuboid, and the three cuneiforms—presents a complex reconstructive challenge for the orthopaedic surgeon. Unlike isolated fractures of the talus or calcaneus, injuries to the midtarsal region are frequently the result of violent, high-energy trauma, such as motor vehicle collisions, industrial crush injuries, or falls from significant heights. Consequently, these injuries rarely occur in isolation; they typically involve multiple bones, severe comminution, and concomitant subluxation or dislocation of one or more midtarsal (Chopart) or tarsometatarsal (Lisfranc) joints.

When these severe injuries heal in a non-anatomic position, the resulting malunion drastically alters the biomechanics of the foot. The primary goal of reconstructive surgery in this region is not necessarily the restoration of perfect radiographic anatomy, but rather the creation of a stable, pain-free, and plantigrade foot that can tolerate normal weight-bearing forces.

Clinical Pearl: In the management of lesser tarsal malunions, functional alignment supersedes perfect anatomical restoration. The primary objective is to eliminate painful plantar pressure points and restore the weight-bearing axis of the foot.

Pathoanatomy and Biomechanics

Understanding the pathoanatomy of tarsal malunions is critical for preoperative planning. The midfoot acts as the keystone of the longitudinal and transverse arches. When violent trauma disrupts this architecture, a predictable pattern of displacement often occurs.

Deformity Patterns

In a typical midtarsal crush injury or fracture-dislocation, the distal fragments (or the distal tarsal rows) are driven and displaced dorsalward. This displacement is exacerbated by the pull of the extrinsic toe extensors and the tibialis anterior. Conversely, the proximal fragments are often driven plantarward.

This multiplanar displacement creates a classic clinical presentation:
* Dorsal Prominence: The dorsally displaced distal fragments overlap the proximal bones, creating a hard, bony prominence on the dorsum of the foot. This bossing frequently leads to difficulty with shoe wear and chronic skin irritation.
* Plantar Mass: The proximal fragments, driven inferiorly, form a rigid mass on the sole of the foot. This disrupts the normal plantar contour, leading to focal pressure areas, intractable plantar keratoses, and severe pain during the stance phase of gait.

Kinematic Consequences

The midtarsal joints (talonavicular and calcaneocuboid) work in concert with the subtalar joint to allow inversion and eversion, adapting the foot to uneven terrain. Malunion in this region invariably leads to a significant, if not complete, loss of these lateral movements. Even if the articular surfaces are not directly involved in the fracture, the altered spatial relationship of the tarsal bones restricts the normal excursion of the midfoot joints.

Clinical Evaluation and Decision Making

The Role of Conservative Management

A critical tenet in the management of tarsal malunions is the timing of surgical intervention. Unless the deformity is exceptionally severe, threatening skin viability, or causing intolerable pain at rest, early operative intervention for an established malunion is generally not advisable.

Surgical Warning: Resist the temptation to operate immediately on a newly consolidated tarsal malunion. A mandatory trial of weight-bearing and conservative management for 6 to 12 months is strongly recommended.

During this 6- to 12-month period, the foot undergoes significant remodeling. Soft tissues adapt, and the patient may spontaneously accommodate to the altered biomechanics through the use of custom orthotics, rigid-sole shoes, or rocker-bottom modifications. Surgery is indicated only when this exhaustive conservative trial fails to relieve painful plantar pressure or when dorsal bossing precludes normal shoe wear.

Preoperative Imaging

Standard weight-bearing radiographs (anteroposterior, lateral, and oblique views) are the starting point. However, plain films severely underestimate the three-dimensional complexity of tarsal malunions.

A fine-cut Computed Tomography (CT) scan with 3D reconstructions is mandatory. The CT scan allows the surgeon to:
1. Assess the degree of articular cartilage damage in the midtarsal and subtalar joints.
2. Quantify the exact degree of dorsal/plantar translation and angular deformity.
3. Evaluate bone stock for potential hardware placement and identify areas requiring structural bone graft.

Surgical Anatomy and Approaches

Access to the lesser tarsals requires meticulous handling of the thin dorsal soft tissue envelope. The choice of approach depends on the specific bones involved.

The Dorsomedial Approach

Used for addressing the navicular, medial cuneiform, and the medial column.
* Incision: A longitudinal incision is made centered over the talonavicular joint, extending distally to the first tarsometatarsal joint, placed just lateral to the tibialis anterior tendon.
* Deep Dissection: The extensor hallucis longus (EHL) and the dorsalis pedis artery/deep peroneal nerve bundle are identified and retracted laterally. The tibialis anterior is retracted medially.
* Exposure: Subperiosteal dissection exposes the dorsal aspect of the navicular and cuneiforms. Care must be taken to preserve the plantar blood supply.

The Dorsolateral Approach

Used for addressing the cuboid and the lateral column.
* Incision: A longitudinal incision is made over the dorsolateral aspect of the foot, centered over the calcaneocuboid joint.
* Deep Dissection: The sural nerve is identified and protected in the subcutaneous tissue. The extensor digitorum brevis (EDB) muscle belly is elevated from its origin on the calcaneus and reflected distally to expose the calcaneocuboid joint and the cuboid.

Operative Techniques: Step-by-Step

The surgical strategy for tarsal malunions falls into two broad categories: joint-sparing corrective osteotomy and midtarsal arthrodesis.

1. Corrective Osteotomy (Joint-Sparing)

Occasionally, if the articular surfaces of the midtarsal joints are pristine and the malunion is strictly extra-articular, lateral movements of the foot can be partially preserved by performing an osteotomy through the old fracture site.

• Indications: Young patients, isolated extra-articular malunion, preserved joint space on CT, and flexible adjacent joints.
• Technique: The old fracture line is identified and recreated using an oscillating saw and osteotomes. The fragments are mobilized, and the dorsal/plantar overlap is corrected.
• Limitations: Even with successful extra-articular osteotomy, lateral movements are usually permanently diminished due to soft tissue contractures and capsular scarring. Therefore, this technique is rarely applicable in severe crush injuries.

2. Midtarsal Arthrodesis (The Gold Standard)

Because lateral movements are often already partially or completely lost, and traumatic arthritis is either present or inevitable, partial or total resection and arthrodesis of one or more tarsal joints is the most frequent requirement.

Clinical Pearl: Arthrodesis that entirely eliminates lateral midfoot motion does not add much to the patient's existing disability, especially in young people, provided the foot is rendered plantigrade and pain-free.

Step 1: Joint Preparation and Resection

• The involved joints (e.g., naviculocuneiform, calcaneocuboid) are exposed.
• Using a combination of osteotomes, rongeurs, and curettes, the remaining articular cartilage and subchondral bone are aggressively resected down to bleeding cancellous bone.
• To correct the dorsal prominence and plantar mass, a wedge resection may be necessary. A dorsally based wedge is often removed to correct a plantarflexed proximal fragment, allowing the foot to be brought up into a neutral, plantigrade position.

Step 2: Preservation of the Subtalar Joint

A critical biomechanical principle must be observed: When the subtalar joint is not involved in the post-traumatic arthrosis, its motion must be preserved.
* The surgeon should limit the fusion strictly to the midtarsal joints (Chopart and distal).
* Fusing an uninvolved subtalar joint unnecessarily stiffens the hindfoot and drastically increases the risk of adjacent segment disease at the ankle joint.

Step 3: Structural Restoration and Bone Grafting

Because violent trauma often results in bone loss or severe comminution, restoring the length of the medial or lateral column is vital to prevent secondary deformities (e.g., acquired flatfoot or cavovarus deformity).
* If a void is created after correcting the overlap and angulation, a structural tricortical iliac crest bone graft (ICBG) or a robust allograft must be intercalated into the defect.
* Copious cancellous autograft (harvested from the proximal tibia or calcaneus) should be packed into all interstices to promote union.

Step 4: Internal Fixation

Rigid internal fixation is paramount to maintain the corrected alignment and achieve arthrodesis.
* Medial Column: Typically stabilized using robust, low-profile dorsal bridging plates. Alternatively, large fragment (4.5mm or 6.5mm) partially threaded cannulated screws can be used as "home run" screws from the cuneiforms into the navicular or talus.
* Lateral Column: The calcaneocuboid joint is best stabilized with a dedicated locking plate. If length has been restored with a structural graft, a bridging plate provides superior biomechanical stability compared to isolated screw fixation.
* Compression: Whenever possible, eccentric drilling or compression devices should be utilized to compress the arthrodesis sites before final plate fixation.

Postoperative Rehabilitation Protocol

The success of a midtarsal reconstruction relies heavily on strict adherence to postoperative protocols. The reconstructed midfoot is highly susceptible to hardware failure and nonunion if loaded prematurely.

Phase 1: Maximum Protection (Weeks 0-6)

• The patient is placed in a well-padded, short-leg splint in the operating room.
• Strict non-weight-bearing (NWB) status is enforced.
• At 2 weeks, sutures are removed, and the patient is transitioned to a rigid fiberglass cast or a locked CAM boot, remaining strictly NWB.

Phase 2: Progressive Loading (Weeks 6-12)

• At 6 weeks, clinical and radiographic evaluations are performed. If there is evidence of early consolidation and no hardware complication, the patient may begin progressive partial weight-bearing (PWB) in a CAM boot.
• Physical therapy is initiated, focusing on active range of motion of the ankle and toes, as well as isometric strengthening of the extrinsic foot musculature.

Phase 3: Maturation and Orthotic Support (Weeks 12+)

• Once radiographic union is confirmed (often requiring a follow-up CT scan at 12 weeks), the patient is transitioned to regular footwear.
• A custom-molded, rigid-sole orthotic with a well-contoured arch support is highly recommended for the first year postoperatively to protect the arthrodesis mass from excessive bending moments.

Complications and Pitfalls

Nonunion

The midfoot has a notoriously tenuous blood supply, particularly the navicular. Nonunion rates in midtarsal arthrodesis can approach 10-15%.
* Prevention: Meticulous joint preparation, use of autologous bone graft, and rigid fixation.
* Management: Asymptomatic nonunions may be observed. Symptomatic nonunions require revision surgery with hardware exchange and biological augmentation (e.g., bone morphogenetic protein, BMP-2).

Hardware Prominence

Due to the thin dorsal soft tissue envelope, dorsal plates and screw heads frequently become prominent and irritate the skin or extensor tendons once the postoperative edema subsides.
* Prevention: Use low-profile, anatomically contoured plates. Countersink screw heads where possible.
* Management: Routine hardware removal is not recommended, but targeted removal may be performed after 12-18 months if the arthrodesis is solidly united and the hardware is causing focal pain.

Adjacent Segment Disease

Fusing the midtarsal joints alters the kinematics of the foot, placing increased stress on the adjacent tarsometatarsal (Lisfranc) and subtalar joints. Over time, this can lead to accelerated osteoarthritis in these adjacent segments.
* Prevention: Preserve the subtalar joint whenever possible. Ensure the foot is fused in a perfectly plantigrade position; a foot fused in varus or equinus will rapidly destroy the adjacent joints.

Conclusion

The operative management of tarsal malunions is a formidable undertaking reserved for patients who have failed an extensive trial of conservative management. By thoroughly understanding the pathoanatomy of the dorsal prominence and plantar mass, the surgeon can execute a precise midtarsal arthrodesis. While lateral midfoot motion is inevitably sacrificed, the restoration of a stable, plantigrade, and pain-free foot provides a profound improvement in the patient's quality of life and functional capacity.