Operative Management of Pes Planus and Tarsal Coalition: A Comprehensive Surgical Guide

Comprehensive Introduction and Patho-Epidemiology

The surgical management of pes planus (flatfoot) and tarsal coalition represents a highly intricate cornerstone of reconstructive foot and ankle surgery, demanding a profound understanding of three-dimensional hindfoot kinematics. Historically, the literature—ranging from the seminal, foundational works of Evans, Grice, and Kidner to the modern, rigorously quantified biomechanical analyses of Mosca, Sangeorzan, and Cowell—has dictated a progressive, stepwise approach to these complex deformities. We have evolved from isolated, often doomed, soft-tissue plications to comprehensive, multi-planar osseous realignments that respect the center of rotation of angulation (CORA) of the peritalar joints. Pes planus is not a singular, monolithic diagnosis but rather a dynamic spectrum of peritalar subluxations. It ranges from the benign, asymptomatic pediatric flexible flatfoot to the rigid, profoundly debilitating adult-acquired flatfoot deformity (AAFD), now more accurately termed progressive collapsing foot deformity (PCFD).

The patho-epidemiology of pes planus is multifactorial, encompassing genetic, mechanical, and degenerative etiologies. In the pediatric population, flexible pes planus is nearly ubiquitous in infancy, resolving in the majority of children by the first decade of life as ligamentous laxity decreases and neuromuscular control matures. However, a persistent subset of patients—frequently those with underlying collagenopathies such as Marfan syndrome, Ehlers-Danlos syndrome, or generalized benign joint hypermobility—will retain a symptomatic, structurally deficient medial longitudinal arch. In the adult population, the etiology shifts dramatically toward degenerative tendinosis and ligamentous attenuation. The incidence of AAFD/PCFD is highest among women in their fifth and sixth decades, strongly correlated with obesity, hypertension, diabetes mellitus, and seronegative arthropathies. The chronic, repetitive microtrauma to the posterior tibial tendon (PTT) and the spring ligament complex ultimately overwhelms the intrinsic repair mechanisms, leading to macroscopic failure and architectural collapse.

Conversely, tarsal coalition presents as a distinct patho-epidemiological entity, classically characterized as a "peroneal spastic flatfoot." This condition manifests as a rigid, painful hindfoot secondary to anomalous mesenchymal segmentation during embryogenesis. The failure of normal joint cavitation between the 8th and 12th weeks of fetal development results in a syndesmotic, synchondrotic, or synostotic bridge between adjacent tarsal bones. The true incidence of tarsal coalition is estimated to be between 1% and 13% in the general population, with a significant proportion remaining asymptomatic throughout life. Inheritance is generally considered to be autosomal dominant with variable, incomplete penetrance. Calcaneonavicular (CN) and talocalcaneal (TC) coalitions account for over 90% of all cases, presenting at distinct developmental windows corresponding to the ossification of the respective coalitions: CN coalitions typically become symptomatic between ages 8 and 12, whereas TC coalitions (predominantly involving the middle facet) ossify and present later, between ages 12 and 16.

The modern paradigm shift in the surgical management of both pes planus and tarsal coalition emphasizes the preservation of peritalar motion whenever biologically and mechanically feasible. The historical reliance on early, preemptive arthrodesis has been largely supplanted by joint-sparing osteotomies and aggressive soft-tissue reconstructions. Arthrodesis is now judiciously reserved for end-stage, rigid deformities complicated by advanced osteoarthritis. This masterclass text delineates the evidence-based surgical indications, the intricate biomechanical principles governing the hindfoot, and the exhaustive, step-by-step operative techniques required to successfully correct these profound architectural collapses while minimizing the risk of catastrophic iatrogenic complications.

Detailed Surgical Anatomy and Biomechanics

A masterful command of the kinematic chain of the hindfoot is paramount for any reconstructive foot and ankle surgeon. The talocalcaneonavicular (TCN) joint functions as the acetabulum pedis or coxa pedis, a dynamic, multi-articulating socket that dictates the positioning of the midfoot and forefoot relative to the leg. The talus, devoid of any direct tendinous insertions, acts as an intercalary bone, passively responding to the kinetic forces exerted upon the calcaneus and navicular. Normal peritalar motion is a complex, triplanar coupling: subtalar inversion is obligatorily coupled with talonavicular and calcaneocuboid (Chopart's joint) locking, transforming the foot into a rigid lever for terminal stance and push-off. Conversely, subtalar eversion unlocks Chopart's joint, allowing the midfoot to become a supple shock absorber during initial heel strike.

The structural integrity of this system relies on a delicate interplay between static and dynamic stabilizers. The primary static stabilizers include the spring ligament complex, the plantar fascia, the long and short plantar ligaments, and the deltoid ligament complex. The spring ligament (plantar calcaneonavicular ligament) is arguably the most critical static restraint against talar head plantarflexion and medial subluxation. It is composed of three distinct anatomical bands: the superomedial, the inferior, and the third (medioplantar) calcaneonavicular ligaments. The superomedial band is the thickest and most frequently attenuated in progressive collapsing foot deformity. The dynamic stabilizers are spearheaded by the posterior tibial tendon (PTT), which acts as the primary invertor of the hindfoot and elevator of the medial longitudinal arch. The PTT works in direct antagonism to the peroneus brevis and is synergistically assisted by the flexor digitorum longus (FDL), the flexor hallucis longus (FHL), and the intrinsic plantar musculature.

In the pathogenesis of pes planus, the failure of these stabilizers leads to a highly predictable, sequential cascade of multi-planar collapse. The initial insult typically involves PTT tendinosis and spring ligament attenuation. As these medial restraints fail, the calcaneus is allowed to evert beneath the talus, initiating the first stage of deformity: Hindfoot Valgus. This valgus alignment shifts the mechanical axis of the Achilles tendon laterally, converting it from a secondary invertor into a deforming evertor force. Subsequently, the talar head loses its medial and plantar support, plantarflexing and medially rotating, while the navicular subluxates dorsolaterally. This represents the second stage: Midfoot Abduction, clinically visualized as the "too many toes" sign. Finally, to maintain a plantigrade foot and keep the medial column on the ground, the forefoot supinates relative to the hindfoot. Over time, soft tissue contractures and osseous adaptations render this compensatory Forefoot Supinatus a fixed, rigid deformity.

Tarsal coalitions drastically alter this normal biomechanical environment by physically tethering the peritalar joints, thereby abolishing the normal coupling mechanism. When the subtalar or talonavicular joint is locked by a coalition, the physiologic forces of walking are abnormally transmitted to adjacent, non-tethered joints. This leads to altered contact pressures, microtrauma, and accelerated degenerative joint disease, particularly at the talonavicular and calcaneocuboid articulations. The classic "peroneal spasticity" observed in these patients is not a true upper motor neuron spasticity, but rather an adaptive, reflex muscle guarding. The peroneal muscles contract in a sustained, tonic fashion to splint the painful, inflamed peritalar joints, holding the foot in a rigid, pronated, and valgus position to minimize motion through the arthritic or synchondrotic segments.

Exhaustive Indications and Contraindications

Surgical intervention for pes planus and tarsal coalition is strictly reserved for patients who have demonstrably failed a comprehensive, meticulously documented regimen of conservative management. Non-operative modalities must include, at a minimum, customized rigid or semi-rigid orthoses (e.g., University of California Biomechanics Laboratory [UCBL] orthoses, supramalleolar orthoses [SMO], or Arizona braces), targeted physical therapy focusing on eccentric PTT strengthening and Achilles stretching, non-steroidal anti-inflammatory drugs (NSAIDs), and activity modification. The transition from conservative to operative management hinges on a nuanced clinical assessment differentiating a flexible, reducible deformity from a rigid, arthritic one.

Joint-sparing procedures, such as the medializing calcaneal osteotomy (MDCO), lateral column lengthening (LCL), and medial cuneiform plantarflexing osteotomy (Cotton procedure), are indicated exclusively for flexible deformities where the peritalar joints are free of advanced degenerative changes. The goal of these procedures is to shift the mechanical axis, restore the functional length of the osseous columns, and recreate the windlass mechanism. Conversely, joint-sacrificing procedures, such as isolated subtalar arthrodesis, talonavicular arthrodesis, or the definitive triple arthrodesis, are indicated when the deformity is rigid, when the deformity cannot be manually reduced to a plantigrade position, or when severe osteoarthritis is present on radiographic evaluation.

For tarsal coalitions, the decision to resect the coalition versus proceeding directly to arthrodesis depends primarily on the patient's age, the anatomical extent of the coalition, and the presence of secondary osteoarthritic changes. Resection with interpositional grafting is the gold standard for younger patients with localized coalitions (typically less than 50% of the posterior facet for TC coalitions) and preserved adjacent joint cartilage. Arthrodesis is mandated if the coalition is massive, if prior resection has failed, or if the patient exhibits advanced degenerative changes in the Chopart or subtalar joints.

Pre-Operative Planning, Templating, and Patient Positioning

Meticulous pre-operative planning is the bedrock of successful deformity correction. The clinical evaluation must begin with a comprehensive gait analysis, observing the patient for the presence of an antalgic gait, early heel rise, and the dynamic "too many toes" sign. The single-heel rise test is mandatory: an inability to perform a single-heel rise, or the failure of the calcaneus to invert during the rise, indicates severe dysfunction or rupture of the PTT. The flexibility of the hindfoot must be assessed with the patient seated and prone. Furthermore, the reducibility of the forefoot supinatus is evaluated using the Silfverskiöld test (to differentiate gastrocnemius tightness from Achilles contracture) and the Hubscher maneuver (Jack's test) to assess the integrity of the windlass mechanism. A fixed forefoot supinatus that does not reduce when the hindfoot is placed in neutral will doom any hindfoot correction to failure, as the patient will be forced to walk on the lateral border of the foot, necessitating a concurrent medial column procedure.

Radiographic evaluation requires strict, weight-bearing (simulated functional) imaging. The standard series includes weight-bearing anteroposterior (AP), lateral, and Harris axial heel views. On the AP view, the surgeon must quantify the talonavicular coverage angle (normal is <7 degrees); uncovering greater than 30% strongly dictates the need for a lateral column lengthening. Kite's angle (the talocalcaneal angle) is assessed for divergence. On the lateral view, Meary's angle (the longitudinal axis of the talus intersecting the first metatarsal) should be 0 degrees; in pes planus, it intersects plantarly, indicating a collapse at the talonavicular or naviculocuneiform joints. The calcaneal pitch is evaluated for loss of inclination. Advanced imaging is indispensable in the modern era. Weight-bearing computed tomography (WBCT) is rapidly becoming the gold standard for three-dimensional assessment of the acetabulum pedis and for precise mapping of tarsal coalitions. For coalitions, CT identifies the "C-sign" for TC coalitions and the "anteater nose" sign for CN coalitions, allowing the surgeon to calculate the exact percentage of joint involvement. Magnetic resonance imaging (MRI) is utilized to assess the macroscopic integrity of the PTT, the spring ligament complex, and the presence of subchondral bone marrow edema indicative of early degenerative changes.

Pre-operative templating involves utilizing digital software to plan osteotomy angles, calculate the exact millimeter of translation required for an MDCO, and determine the precise trapezoidal dimensions of the structural graft needed for an Evans procedure. Over-lengthening the lateral column by even 2-3 millimeters can result in catastrophic lateral column overload and calcaneocuboid subluxation. Templating ensures the surgeon has the correct size allografts, specialized compression plates, and cannulated screw systems available in the operative suite.

Patient positioning in the operating room must facilitate simultaneous access to the medial, lateral, and posterior aspects of the foot and ankle. The patient is typically positioned supine. A critical maneuver is the placement of a large gel bump under the ipsilateral hemipelvis. This internally rotates the lower extremity, bringing the lateral border of the foot directly anterior, which is essential for the Ollier approach or the lateral calcaneal incision. A radiolucent triangle or a sterile ramp is placed under the calf to allow for unobstructed lateral fluoroscopic imaging. A well-padded thigh tourniquet is applied, and the limb is prepped and draped beyond the knee to allow for the assessment of the tibial tubercle and patella during intraoperative alignment checks. The fluoroscopy C-arm is positioned on the contralateral side of the table, draped sterilely, and must be capable of swinging freely to obtain exact AP, lateral, and axial intraoperative views.

Step-by-Step Surgical Approach and Fixation Technique

Lateral Column Lengthening (Evans and Mosca Procedures)

Originally described by Evans and later refined by Mosca to preserve the calcaneocuboid articulation, lateral column lengthening corrects midfoot abduction and hindfoot valgus by physically elongating the lateral border of the foot. This tensioning of the plantar fascia and spring ligament through the "windlass" mechanism indirectly elevates the medial longitudinal arch and pulls the navicular medially, reducing the talonavicular joint.

The surgical approach utilizes an oblique incision over the sinus tarsi, extending from the distal tip of the lateral malleolus toward the base of the fourth metatarsal (the classic Ollier approach). The surgeon must meticulously dissect through the subcutaneous tissues, carefully identifying and retracting the sural nerve and the peroneal tendons inferiorly, and the intermediate dorsal cutaneous branch of the superficial peroneal nerve superiorly. The extensor digitorum brevis (EDB) muscle belly is identified, sharply elevated off the calcaneus, and reflected distally to expose the calcaneocuboid (CC) joint and the anterior process of the calcaneus.

The osteotomy placement is critical. A Keith needle is placed into the CC joint under fluoroscopy. The osteotomy is initiated exactly 1.5 cm proximal to the CC joint line, running strictly parallel to the articular surface. Using an oscillating saw equipped with a thin blade, the surgeon cuts the lateral cortex, proceeding medially. It is imperative to leave the medial calcaneal cortex intact to act as a resilient periosteal hinge; completing the cut through the medial cortex destabilizes the anterior process and risks graft extrusion. A lamina spreader or a specialized distraction pin system is inserted into the osteotomy. Gentle, progressive distraction is applied. The surgeon must clinically observe the foot: as the lateral column lengthens, the midfoot abduction corrects, and the medial arch spontaneously reconstitutes.

A tricortical structural graft is then harvested from the ipsilateral iliac crest, or, more commonly in modern practice, a precisely sized, freeze-dried allograft wedge (typically 8 to 12 mm in width) is utilized. The graft is meticulously shaped into a trapezoid to fit the distracted defect perfectly. It is impacted into place, and the lamina spreader is removed, allowing the native tissue tension to compress the graft. While the graft is often stable under this compression, rigid internal fixation utilizing a cervical spine locking plate, a dedicated Evans step-plate, or a fully threaded cortical screw is highly recommended to prevent catastrophic graft extrusion or micromotion leading to nonunion.

Medializing Calcaneal Osteotomy (Koutsogiannis Procedure)

For patients presenting with flexible hindfoot valgus without severe, unyielding midfoot abduction, a medial displacement calcaneal osteotomy (MDCO) is the workhorse procedure. By physically translating the calcaneal tuberosity medially, the mechanical axis of the Achilles tendon is shifted medial to the subtalar joint axis. This profoundly alters the biomechanics, converting the Achilles from a deforming evertor into a powerful, dynamic invertor of the hindfoot, thereby unloading the medial soft tissue structures.

The surgical approach involves an oblique lateral incision positioned posterior to the peroneal tendons and the sural nerve, angled at approximately 45 degrees to the plantar aspect of the foot, mirroring the planned osteotomy cut. Dissection is carried down sharply to the periosteum of the calcaneal tuberosity. The surgeon must maintain a strict subperiosteal plane to avoid injury to the sural nerve laterally and the medial neurovascular bundle medially. Hohmann retractors are placed superiorly and inferiorly over the calcaneal tuberosity to protect the surrounding soft tissues.

Using a sagittal saw, the osteotomy is performed at a 45-degree angle to the plantar surface of the foot. The trajectory must be carefully planned to ensure the cut is entirely posterior to the posterior facet of the subtalar joint, preventing iatrogenic intra-articular damage. The saw blade is passed through the lateral cortex and cancellous bone. The medial cortex is then carefully completed using a broad, thin osteotome to avoid plunging into the medial neurovascular structures. Once the osteotomy is complete, a periosteal elevator is inserted into the cut, and the posterior tuberosity is manually translated medially by 10 to 15 mm (which equates to approximately 50% of the calcaneal width).

Fixation is achieved by securing the translated osteotomy with one or two large-fragment (6.5 mm or 7.3 mm) cannulated, partially threaded screws. Guide wires are driven from the posterior-inferior aspect of the heel, crossing the osteotomy site perpendicular to the cut, and directed toward the anterior process of the calcaneus or the base of the calcaneocuboid joint. Fluoroscopy confirms the medial translation on the axial Harris heel view and verifies that the screws do not violate the subtalar joint on the lateral view. The screws are advanced over the wires to achieve rigid, interfragmentary compression.

Modified Kidner Procedure and Medial Soft Tissue Reconstruction

The presence of an accessory navicular (os tibiale externum) drastically alters the insertion footprint and the vector of the posterior tibial tendon. The tendon frequently inserts into the accessory ossicle rather than the primary navicular tuberosity, weakening its mechanical advantage, causing localized prominence, and predisposing the patient to early PTT tendinosis and flatfoot. The Modified Kidner procedure aims to excise the offending ossicle and restore the physiological tension and insertion of the PTT.

A medial longitudinal incision is centered directly over the prominent navicular tuberosity, extending proximally along the course of the PTT. The superficial fascia is incised, and the PTT is identified as it courses posterior to the medial malleolus and inserts into the accessory bone. A longitudinal incision is made directly in line with the fibers of the PTT over the accessory navicular. Using a #15 scalpel and small, sharp osteotomes, the surgeon carefully "shells out" the accessory navicular from within the tendon substance. It is crucial to preserve the continuity of the plantar fibers of the PTT, which continue distally to insert onto the cuneiforms and metatarsal bases.

Once the accessory navicular is excised, the primary navicular tuberosity is exposed. The prominent medial flare of the primary navicular is aggressively resected using a sagittal saw or a high-speed burr until it is completely flush with the medial cuneiform. This prevents post-operative shoe wear irritation. The medial aspect of the navicular is then decorticated to expose a bleeding cancellous bone bed, which is essential for tendon-to-bone healing.

The PTT is then advanced anteriorly and inferiorly to restore its arch-supporting function. Modern fixation utilizes biocomposite or titanium suture anchors. One or two double-loaded suture anchors are placed into the plantar-medial aspect of the decorticated primary navicular. The sutures are passed through the substance of the PTT using a locking Krackow or Mason-Allen configuration. The foot is held in strict inversion and slight plantarflexion as the sutures are tied, firmly securing the tendon against the bleeding bone bed under physiological tension.

Triple Arthrodesis for Rigid Deformity

When the peritalar deformity becomes rigid, irreducible, and complicated by advanced osteoarthritis (Stage III/IV AAFD), joint-sparing osteotomies are strictly contraindicated. In these scenarios, arthrodesis becomes the gold standard. A triple arthrodesis involves the systematic fusion of the subtalar, talonavicular (TN), and calcaneocuboid (CC) joints to realign the hindfoot and eliminate painful motion.

The procedure requires a dual-incision technique. A lateral Ollier approach is utilized to access the subtalar and CC joints, while a medial utility approach (extending from the medial malleolus to the medial cuneiform) is used to access the TN joint. Meticulous soft tissue handling is required to prevent wound necrosis, maintaining a broad skin bridge between the two incisions.

Joint preparation is the most critical phase of the operation. All articular cartilage must be completely denuded from the TN, CC, and subtalar joints. The surgeon utilizes a combination of sharp osteotomes, ring curettes, and a high-speed burr to remove the cartilage down to the subchondral bone. The subchondral bone is then aggressively punctated or "fish-scaled" using a small osteotome or drill to expose rich, bleeding cancellous bone. Failure to adequately prepare the joints, particularly the notoriously difficult talonavicular joint, is the leading cause of nonunion.

The correction of the deformity must follow a strict sequence. First, the hindfoot valgus is corrected at the subtalar joint by translating the calcaneus medially and rotating it out of valgus. Second, the talonavicular joint is reduced by plantarflexing the talus (correcting the Meary's angle) and rotating the navicular medially (correcting the uncovering). The CC joint usually aligns passively once the TN and subtalar joints are reduced. Fixation begins at the subtalar joint, utilizing one or two 7.3 mm cannulated screws driven from the calcaneal tuberosity up into the talar dome. The TN joint is then compressed and fixed using two 4.5 mm or 5.0 mm screws, or a specialized TN compression plate. Finally, the CC joint is secured with a single 4.5 mm screw or nitinol compression staples. Intraoperative fluoroscopy must confirm the restoration of the cyma line and the absolute rigid compression of all three arthrodesis sites.

Tarsal Coalition Resection Techniques

Tarsal coalitions restrict normal peritalar motion, leading to adaptive shortening of the peroneal tendons and a rigid, painful flatfoot. Resection is the primary treatment for symptomatic calcaneonavicular (CN) and talocalcaneal (TC) middle facet coalitions in younger patients without secondary arthritis.

Calcaneonavicular Coalition Resection:
The patient is positioned supine with a bump under the hip. A lateral Ollier incision is made. The EDB muscle belly is elevated proximally to expose the abnormal bony or cartilaginous bridge between the anterior process of the calcaneus and the lateral aspect of the navicular. Using a sagittal saw and rongeurs, the surgeon must resect a generous, rectangular block of bone—at least 1.5 cm to 2.0 cm wide—to completely eradicate the coalition. The resection is only considered complete when normal, pristine articular cartilage is visualized on the talar head medially and the cuboid distally. To prevent the notorious complication of recurrence and re-ossification, an interpositional material must be placed into the defect. The most robust technique involves mobilizing the EDB muscle belly, passing a heavy suture through its distal end, and drawing it deep into the resection cavity, securing it with drill holes or a suture anchor into the calcaneus or navicular.

Talocalcaneal (Middle Facet) Coalition Resection:
This procedure is significantly more hazardous due to the proximity of critical neurovascular structures. A medial longitudinal incision is made inferior to the medial malleolus, following the course of the PTT. The PTT is retracted dorsally, while the flexor digitorum longus (FDL) and the posterior tibial neurovascular bundle are carefully mobilized and retracted plantarward using blunt mini-Hohmann retractors. The flexor hallucis longus (FHL) runs directly plantar to the sustentaculum tali and is at extreme risk during this resection. The coalition replaces the normal middle facet, appearing as a continuous bridge between the medial talus and the sustentaculum tali. Using a high-speed burr and small, curved osteotomes, the surgeon resects the coalition from medial to lateral. The resection is complete only when the normal cartilage of the posterior facet is visualized laterally, and normal, uninhibited subtalar motion is restored intraoperatively. The resulting defect is massive and must be packed tightly with a robust autologous fat graft (harvested from the K