Hereditary motor sensory neuropathies

1. High-Yield Summary

Hereditary motor sensory neuropathies (HMSN), historically and clinically designated Charcot-Marie-Tooth (CMT) disease, represent a genetically heterogeneous group of length-dependent peripheral neuropathies that collectively constitute the most common inherited neuromuscular disorder encountered in orthopaedic practice:

• Genetic & Electrophysiologic Bifurcation: Affecting approximately 1 in 2,500 individuals, HMSN is divided electrodiagnostically into demyelinating types (HMSN I / CMT1, upper extremity motor nerve conduction velocity <38 m/s, most commonly a 1.4-Mb duplication of PMP22 on chromosome 17p11.2) and axonal types (HMSN II / CMT2, preserved conduction velocity >38 m/s with reduced compound muscle action potential amplitudes, classically associated with MFN2 mutations).
• Pathomechanics of Cavovarus Deformity: Progressive musculoskeletal deformity follows an insidious, selective muscular imbalance: denervation and weakness of the tibialis anterior (TA) is overpowered by a strong peroneus longus (PL), driving acute plantarflexion of the first metatarsal (forefoot cavus); denervation of the peroneus brevis (PB) is overpowered by a strong tibialis posterior (PT), driving hindfoot varus and adduction. Secondary intrinsic muscle wasting causes clawing of the digits and plantar fascial contracture.
• The Coleman Block Test as Surgical Pivot: The Coleman block test is the definitive clinical maneuver determining surgical strategy. If the hindfoot varus corrects to neutral or physiologic valgus when the first ray drops off the lateral block, the deformity is flexible and forefoot-driven, indicating joint-preserving reconstruction. If varus persists, the deformity is rigid and hindfoot-driven, mandating bony realignment or arthrodesis.
• Joint-Preserving Reconstructive Algorithm: For flexible and semi-rigid deformities without advanced osteoarthritis, joint-preserving surgery is the standard of care. The systematic sequence includes: (1) plantar fascia release and gastrocnemius recession; (2) first metatarsal dorsal closing-wedge osteotomy; (3) tendon transfers (peroneus longus to brevis, posterior tibial tendon transferred to the lateral cuneiform); and (4) lateralizing calcaneal osteotomy (Dwyer or sliding translational osteotomy).
• Salvage Arthrodesis & Pharmacologic Safeguards: Triple arthrodesis is strictly reserved for fixed, non-braceable deformities with end-stage peritalar osteoarthritis, given long-term adjacent-segment ankle arthrosis rates of 40% to 75% at 20 to 30 years. Systemically, neurotoxic pharmaceuticals—specifically vincristine—are absolutely contraindicated, as accidental exposure can trigger catastrophic, rapid axonal necrosis and irreversible quadriparesis.

2. Anatomy

Muscular Imbalance Mechanics & Vector Forces

The progression of the cavovarus foot in HMSN is governed by a predictable, length-dependent motor denervation pattern that disrupts the reciprocal balance between agonist and antagonist muscle groups across the foot and ankle:

• Tibialis Anterior versus Peroneus Longus (Sagittal Plane Driver): The tibialis anterior (deep peroneal nerve, L4-L5) undergoes early neurogenic atrophy and weakness. Its physiological antagonist, the peroneus longus (superficial peroneal nerve, S1), maintains preserved motor innervation until late stages. Inserting onto the plantar base of the first metatarsal and the medial cuneiform, the unopposed contraction of the peroneus longus forcefully plantarflexes the first ray. This plantarflexed first ray acts as a rigid anterior-medial pillar during stance phase, forming the primary apex-dorsal driver of forefoot cavus.
• Peroneus Brevis versus Tibialis Posterior (Coronal Plane Driver): The peroneus brevis (superficial peroneal nerve, L5-S1), the primary dynamic evertor of the subtalar joint inserting on the fifth metatarsal tuberosity, atrophies early. Conversely, the tibialis posterior (tibial nerve, L4-L5), inserting broadly across the navicular tuberosity, cuneiforms, and cuboid, retains robust strength. The unopposed adduction and inversion vector of the tibialis posterior tilts the calcaneus into rigid varus and locks the transverse tarsal (Chopart) joint complex into supination.
• Intrinsic Foot Muscular Atrophy & Extrinsic Substitution: Progressive denervation of the intrinsic pedis musculature (lumbricals, interossei, and flexor digitorum brevis; medial and lateral plantar nerves) results in loss of active metatarsophalangeal (MTP) joint flexion and interphalangeal (IP) joint extension. In an effort to clear the foot during swing phase, the long toe extensors (extensor hallucis longus [EHL] and extensor digitorum longus [EDL]) dynamically substitute for the weak tibialis anterior, hyperextending the MTP joints. The long flexors (flexor hallucis longus [FHL] and flexor digitorum longus [FDL]) subsequently flex the IP joints against resistance, producing rigid claw toes, cock-up hallux deformity, and subluxation of the plantar fat pad anterior to the metatarsal heads.
• Plantar Fascial Contracture & The Windlass Mechanism: Unopposed plantar forces and chronic elevation of the longitudinal arch induce progressive thickening, fibrosis, and contracture of the central and medial bands of the plantar aponeurosis. This static tethering prevents sagittal plane flattening of the arch during loading, locking the midfoot in rigid cavus.

Neurovascular Danger Zones

Surgical reconstruction of the cavovarus foot involves extensive soft-tissue releases, tendon harvesting, and osteotomies that traverse narrow anatomical corridors with critical neurovascular structures at risk:

• Sural Nerve Danger Zone: Descends along the posterolateral border of the Achilles tendon, passes 1.0 to 1.5 cm inferior to the tip of the lateral malleolus, and courses anteriorly along the lateral calcaneal wall above the peroneal tendons. The sural nerve is directly endangered during lateral calcaneal osteotomies (Dwyer closing wedge or sliding lateral osteotomy) and lateral percutaneous pin or screw insertion. Transection or traction neuropraxia leads to painful neuromas and dysesthesia along the lateral hindfoot and fifth digit. Dissection along the lateral calcaneus must remain strictly subperiosteal beneath full-thickness flaps.
• Superficial Peroneal Nerve (SPN) Danger Zone: Pierces the crural fascia approximately 10 to 12 cm proximal to the lateral malleolus, dividing into the medial and intermediate dorsal cutaneous nerves. Its branches cross directly superficial to the extensor retinaculum and course across the dorsal midfoot and tarsometatarsal joints. These cutaneous branches are vulnerable during dorsal closing-wedge osteotomy of the first metatarsal, midfoot osteotomies, and anterior tendon anchoring corridors. Incisions over the first metatarsal must be placed strictly medial or dorsomedial, utilizing blunt dissection through the subcutaneous plane.
• Deep Peroneal Nerve (DPN) & Dorsalis Pedis Artery: Traverse the anterior compartment beneath the superior and inferior extensor retinacula, descending between the EHL and EDL tendons over the talonavicular and tarsometatarsal joints. The neurovascular bundle is at extreme risk during anterior routing of the posterior tibial tendon through the interosseous membrane and during fixation into the lateral or middle cuneiform. A wide, tension-free window in the interosseous membrane proximal to the syndesmosis is mandatory to prevent compressive impingement of the deep peroneal nerve and anterior tibial vessels.
• Tibial Nerve & Tarsal Tunnel Danger Zone: Courses behind the medial malleolus beneath the flexor retinaculum, dividing into the medial plantar, lateral plantar, and inferior calcaneal (Baxter) nerves. The medial neurovascular bundle is threatened during medial soft-tissue releases, harvesting of the posterior tibial tendon, and complete oscillating saw cuts through the medial cortex of the calcaneus during sliding or closing-wedge osteotomies. The medial calcaneal cortex must be completed using manual osteotomes under direct tactile control with a protective subperiosteal retractor placed along the medial wall.

Internervous Planes & Surgical Corridors

Safe operative exposure of the cavovarus foot relies on anatomical internervous planes that minimize denervation and tissue necrosis:

• Lateral Calcaneal Corridor: Utilized for lateralizing calcaneal osteotomies and subtalar exposure. The plane lies between the sural nerve (posterolateral sensory distribution) and the intermediate dorsal cutaneous branch of the superficial peroneal nerve (anterolateral sensory distribution). Elevation of a single, full-thickness subperiosteal sleeve down to the osseous lateral calcaneal wall protects the peroneal tendon sheath and sural nerve arborizations.
• Medial Midfoot Corridor: Utilized for posterior tibial tendon harvesting and talonavicular capsulotomy. The interval is bounded anteriorly by the saphenous nerve and great saphenous vein and posteriorly by the posterior tibial neurovascular bundle within the tarsal tunnel. Incisions are centered directly over the navicular tuberosity, remaining subperiosteal along the insertion of the posterior tibial tendon.
• Dorsal Cuneiform Corridor: Utilized for transosseous anchoring of tendon transfers. The corridor is situated between the lateral branch of the deep peroneal nerve (medially) and the intermediate dorsal cutaneous branch of the superficial peroneal nerve (laterally). Subcutaneous tissues are retracted together with the extensor digitorum brevis belly.
• Crural Interosseous Membrane Window: Created 4 to 6 cm proximal to the ankle joint syndesmosis. The interosseous membrane is incised longitudinally over a length of 4 to 5 cm between the tibia and fibula, maintaining direct subperiosteal proximity to the posterior and lateral tibial cortex to safeguard the anterior tibial vascular arcade.

Critical Bony Landmarks & Topography

Accurate skeletal correction requires orientation based on fixed osseous landmarks:

• Lateral Calcaneal Wall & Peroneal Tubercle: The retrotrochlear eminence and peroneal tubercle guide the trajectory of calcaneal osteotomies, which must pass 1.0 to 1.5 cm posterior to the posterior facet of the subtalar joint at an angle 45 degrees oblique to the plantar aspect of the heel.
• First Metatarsal Base & Medial Cuneiform: The first tarsometatarsal (Lisfranc) joint marks the proximal limit for the dorsal closing-wedge osteotomy. The osteotomy is positioned 1.0 cm distal to the joint line to preserve subchondral bone stock for staple or plate purchase.
• Navicular Tuberosity & Sustentaculum Tali: Mark the medial apex of the midfoot and hindfoot, guiding posterior tibial tendon detachment and medial joint line verification.
• Fifth Metatarsal Tuberosity: Serves as the primary insertion of the peroneus brevis and represents a frequent site of secondary avulsion or stress fractures due to chronic lateral border weightbearing.

3. Pathogenesis

Molecular Genetics & Cellular Pathobiology

Hereditary motor sensory neuropathies encompass an expanding spectrum of monogenic disorders characterized by mutations in genes encoding structural myelin proteins, gap junctions, axonal transport machinery, or mitochondrial fusion regulators:

• Peripheral Myelin Protein 22 (PMP22, Chromosome 17p11.2): A 1.4-Mb tandem duplication on chromosome 17p11.2 containing the PMP22 gene accounts for more than 70% of demyelinating HMSN I cases and approximately 50% of all CMT presentations (designated CMT1A). PMP22 is a 22-kDa tetraspan glycoprotein localized in compact peripheral myelin. Gene duplication leads to PMP22 overexpression, protein misfolding within the endoplasmic reticulum, induction of the unfolded protein response (UPR), and impaired Schwann cell differentiation. Reciprocal heterozygous deletion of the identical 1.4-Mb region results in hereditary neuropathy with liability to pressure palsies (HNPP). Point mutations within PMP22 cause severe demyelinating phenotypes (CMT1E or Dejerine-Sottas syndrome).
• Mitofusin 2 (MFN2, Chromosome 1p36.22): Mutations in MFN2 represent the primary cause of autosomal dominant axonal neuropathy (CMT2A2). Mitofusin 2 is a nuclear-encoded GTPase embedded in the outer mitochondrial membrane, orchestrating mitochondrial fusion, tethering to the endoplasmic reticulum, and kinesin-mediated anterograde mitochondrial axonal transport. MFN2 dysfunction leads to mitochondrial fragmentation, bioenergetic depletion, and progressive dying-back degeneration of the longest peripheral axons.
• Gap Junction Beta 1 / Connexin 32 (GJB1, Chromosome Xq13.1): Encodes connexin 32, a transmembrane protein forming non-compact myelin gap junctions at the nodes of Ranvier and Schmidt-Lanterman incisures. Mutations produce X-linked CMT (CMTX1), resulting in impaired radial metabolic transport across the myelin sheath. Hemizygous males manifest moderate-to-severe childhood-onset sensorimotor neuropathy with intermediate conduction velocities (30 to 40 m/s), whereas heterozygous females exhibit milder, late-onset phenotypes due to variable X-inactivation.
• Myelin Protein Zero (MPZ, Chromosome 1q22): Encodes P0, an immunoglobulin superfamily structural adhesion molecule representing more than 50% of total compact peripheral myelin protein. Point mutations disrupt homophilic adhesion, producing diverse phenotypes ranging from classical demyelinating CMT1B to axonal CMT2I/J and severe congenital hypomyelinating neuropathy.

Demyelinating versus Axonal Biologic Profiles

The cellular pathogenesis dictates distinctive histopathological and neurophysiological profiles between demyelinating and axonal variants:

• Demyelinating Biology (HMSN I / CMT1): Primary Schwann cell dysfunction initiates repetitive cycles of segmental demyelination and remyelination. Proliferating Schwann cells encircle denuded axons in multiple concentric, lamellated layers, creating pathognomonic “onion bulb” formations visible on cross-sectional nerve histology. The loss of myelin thickness and nodal architecture markedly slows salutatory conduction, yielding uniform, symmetrical reduction in motor nerve conduction velocity (<38 m/s, often 15 to 25 m/s). Clinical disability correlates directly with secondary length-dependent axonal loss rather than the degree of conduction slowing itself.
• Axonal Biology (HMSN II / CMT2): Primary disruption involves neurofilament assembly, axonal transport systems, or mitochondrial energetics within the perikaryon or axon. Histology reveals profound loss of large myelinated fibers, axonal sprouting clusters, and Wallerian-like degeneration without onion bulb formation. Conduction velocities remain normal or mildly decreased (>38 m/s, typically 40 to 52 m/s), but compound muscle action potential (CMAP) and sensory nerve action potential (SNAP) amplitudes are markedly attenuated, reflecting progressive distal axonal depletion.

Biomechanical Progression of the Cavovarus Deformity

The progression of the cavovarus foot follows a three-stage biomechanical sequence driven by the “tripod effect” described by Paulos and Coleman:

• The Tripod Concept: The human foot functions mechanically as a three-legged tripod formed by the calcaneal tuberosity posteriorly, the first metatarsal head medially, and the fifth metatarsal head laterally. In HMSN, hyperactive peroneus longus traction drives the first metatarsal into plantarflexion, lowering the anteromedial leg of the tripod relative to the other two points.
• Stage 1 (Forefoot-Driven Compensatory Flexible Varus): During early stance phase, the rigidly plantarflexed first metatarsal head strikes the ground prematurely. To bring the lateral border of the foot and the fifth metatarsal head down to achieve a plantigrade weightbearing platform, the subtalar joint must invert. The hindfoot is forced into secondary compensatory varus. At this stage, the subtalar and transverse tarsal joints remain fully supple; unloading the first ray completely restores the calcaneus to its normal physiologic valgus orientation.
• Stage 2 (Soft-Tissue Adaptation & Semi-Rigid Varus): With persistent ambulation on an inverted foot, adaptive contracture develops within the medial and plantar soft tissues. The plantar fascia, spring ligament complex, superficial deltoid ligament, and posterior tibial tendon shorten and fibrose. Concurrently, the lateral peritalar stabilizers—the calcaneofibular ligament (CFL) and anterior talofibular ligament (ATFL)—are subjected to chronic tensile elongation, leading to lateral mechanical instability. The hindfoot becomes semi-rigid and can no longer be fully reduced by forefoot manipulation alone.
• Stage 3 (Rigid Structural Bony Deformity): Asymmetric joint loading across the peritalar complex induces secondary osseous remodeling. The subtalar articular facets develop adaptive wedging, marginal osteophytes, and subluxation. The talonavicular joint locks into adduction and dorsal subluxation, while the calcaneocuboid joint compresses along its medial margin. The deformity becomes fixed, rigid, and irreversible without direct osseous osteotomy or joint arthrodesis.

4. Natural History

Epidemiology & Demographics

Hereditary motor sensory neuropathies affect approximately 1 in 2,500 individuals globally (prevalence: 40 per 100,000), showing no racial, geographic, or ethnic predilection. CMT1A constitutes roughly 50% of all diagnosed peripheral neuropathies, CMTX1 accounts for 10% to 15%, and CMT2A accounts for approximately 5%. The inheritance pattern is autosomal dominant in the vast majority (70% to 80%), followed by X-linked dominant (10% to 15%) and autosomal recessive (<5% to 10%). Autosomal forms demonstrate equal male-to-female ratios; CMTX1 manifests earlier and with greater functional severity in hemizygous males compared to heterozygous carrier females.

Disease Trajectory & Functional Deterioration

Clinical onset classically manifests within the first to second decade of life. Early childhood presentations (ages 5 to 10 years) are marked by motor clumsiness, poor athletic performance, frequent tripping, and difficulty finding properly fitting footwear due to high arches. The functional progression follows a symmetrical, distal-to-proximal, length-dependent trajectory:

• Lower Extremity Wasting: Neurogenic atrophy of the anterior and lateral leg musculature creates the classic “stork leg” or “inverted champagne bottle” lower leg morphology, sharply demarcated from preserved proximal thigh musculature.
• Gait Alteration: Weakness of the tibialis anterior produces dynamic foot drop, compensated by a high-stepping (steppage) gait with exaggerated hip and knee flexion to prevent toe drag. Heel-walking becomes impossible.
• Upper Extremity Involvement: Approximately 10 to 15 years following the onset of lower extremity symptoms, fine motor impairment develops in the hands. Atrophy of the thenar musculature (abductor pollicis brevis), first dorsal interosseous, and lumbricals produces weakness in pinch strength, difficulty buttoning clothing, handling keys, and writing. A postural or kinetic tremor (Roussy-Lévy phenotype) frequently supervenes.
• Mobility Preservation: Life expectancy is normal. More than 80% of individuals with CMT1A maintain ambulatory capacity throughout adulthood, though approximately 30% to 50% ultimately require orthotic assistance (AFOs) or mobility aids in the fifth to seventh decades. Severe autosomal recessive variants (CMT4) and congenital hypomyelinating forms (HMSN III) exhibit accelerated deterioration, often causing wheelchair dependence by adolescence.

Late Skeletal Arthrosis & Secondary Pathologies

Uncorrected cavovarus alignment shifts peak ground reaction forces onto the lateral border of the foot, generating severe secondary orthopaedic complications:

• Lateral Column Stress Fractures: Excessive mechanical load focused on the fifth metatarsal leads to recurrent stress fractures of the fifth metatarsal diaphysis and base (Jones fracture), as well as stress fractures of the cuboid and distal fibula.
• Chronic Lateral Ankle Instability: Prolonged calcaneal varus stretches the lateral ligamentous complex (calcaneofibular and anterior talofibular ligaments), producing chronic rotational ankle instability and recurrent subtalar subluxation events.
• Peritalar & Ankle Osteoarthritis: Decades of asymmetric articular shear produce end-stage degeneration of the subtalar, talonavicular, and calcaneocuboid joints. In advanced stages, asymmetric medial tibiotalar joint loading leads to secondary ankle osteoarthritis.
• Neuropathic Ulceration & Osteomyelitis: Sensory loss combined with rigid skeletal deformities yields high focal plantar pressures beneath the first and fifth metatarsal heads, the fifth metatarsal tuberosity, and over the dorsal PIP joints of claw toes. Intractable hyperkeratotic callosities break down into deep neuropathic ulcers that can progress to osteomyelitis and require partial ray resection.

5. Clinical Presentation

History

A systematic clinical history must document the temporal onset, functional deficits, and systemic manifestations of peripheral neuropathy:

• Chief Complaints & Walking Impairments: Inquire about childhood clumsiness, frequent unprovoked lateral ankle sprains, “giving way” sensations, difficulty running, and tripping over small surface irregularities. Patients often report shoe-fitting problems, including rapid lateral heel wear and pressure pain over the dorsal aspects of the toes.
• Upper Extremity Symptoms: Screen specifically for loss of manual dexterity: difficulty opening twist jars, buttoning shirts, turning keys, fastening jewelry, or using chopsticks. Inquire about kinetic hand tremors and upper limb fatigue.
• Sensory & Pain Characteristics: Assess for numbness, tingling, and temperature insensitivity in a distal-to-proximal distribution. Deep, aching pain is usually mechanical, originating from overloaded lateral column joints, plantar fasciitis, or tendonitis, rather than true burning dysesthetic neuropathic pain.
• Family Pedigree & Medication Review: Construct a three-generation family tree. Specifically inquire whether relatives possess “high arches,” underwent early foot surgery, or used canes or braces. Review medications to rule out accidental exposure to neurotoxic agents (e.g., vincristine, taxanes, platinum salts, nitrofurantoin, amiodarone).

Physical Examination

Physical examination must integrate comprehensive neurovascular staging with dynamic orthopaedic joint testing:

• Coleman Block Test (Dynamic Hindfoot Flexibility):
  – Technique: The patient stands barefoot with the heel and lateral border of the foot elevated on a 2.5- to 4.0-cm wooden block, allowing the first, second, and third metatarsal heads to hang freely in space off the medial edge.
  – Positive Finding (Flexible Varus): Unloading the first ray eliminates the tripod effect, allowing the hindfoot varus to spontaneously correct into neutral or 3 to 5 degrees of physiologic valgus. This confirms that the deformity is forefoot-driven, indicating joint-preserving soft-tissue and osteotomy procedures [Diagnostic Accuracy: Sensitivity 91%, Specificity 88% for successful peritalar joint preservation].
  – Negative Finding (Rigid Varus): The hindfoot remains locked in varus despite complete elimination of first ray ground contact. This indicates fixed hindfoot pathology requiring calcaneal osteotomy or peritalar arthrodesis.
• Silfverskiöld Test (Equinus Differentiation):
  – Technique: Maximum passive ankle dorsiflexion is measured with the knee in full extension (0 degrees) versus 90 degrees of flexion, while maintaining the subtalar joint strictly locked in neutral to prevent compensatory midfoot dorsiflexion.
  – Interpretation: Ankle dorsiflexion limited to <0 degrees in extension that normalizes to >10 degrees with knee flexion indicates isolated gastrocnemius tightness (indicating Strayer recession). Inability to dorsiflex beyond neutral regardless of knee position confirms combined gastrocnemius-soleus contracture (indicating Achilles tendon lengthening).
• Motor Power Grading (MRC Scale 0–5):
  – Anterior Compartment: Tibialis anterior (typically MRC grade 1 to 3), extensor hallucis longus, and extensor digitorum longus.
  – Lateral Compartment: Peroneus brevis is severely paretic (MRC 0 to 2); peroneus longus is typically preserved (MRC 4 to 5).
  – Posterior Compartment: Tibialis posterior is typically preserved (MRC 4 to 5); gastrocnemius, soleus, FHL, and FDL maintain normal or near-normal power (MRC 4 to 5).
  – Upper Extremity: Test thenar abduction (abductor pollicis brevis), first dorsal interosseous finger abduction, and grip strength.
• Sensory & Reflex Mapping:
  – Sensory Modalities: Assess vibratory perception (128-Hz tuning fork over the medial malleolus and first MTP joint), proprioceptive position sense at the hallux IP joint, light touch (Semmes-Weinstein 5.07 / 10-g monofilament), and pinprick in a length-dependent stocking-glove pattern.
  – Deep Tendon Reflexes: Achilles tendon reflexes (S1) are universally absent (0/4) early; patellar reflexes (L3-L4) diminish or disappear in advanced disease; brachioradialis and triceps reflexes are reduced in CMT1.
• Spine & Upper Extremity Inspection:
  – Hands: Inspect for thenar and hypothenar flattening, guttering of the dorsal interosseous spaces, intrinsic minus posture (“claw hand”), and action tremor.
  – Spine: Perform the Adam forward bend test and scoliometer screening. Neuromuscular scoliosis occurs in 10% to 26% of patients with HMSN, typically manifesting as progressive thoracic curves requiring spinal monitoring.

6. Imaging and Diagnostic Studies

Weightbearing Radiography & Angular Measurements

Radiographic assessment requires standardized, bilateral, full weightbearing radiographs of the foot and ankle, complemented by dedicated hindfoot alignment projections:

• Standard Radiographic Projections: Full weightbearing AP, lateral, and oblique views of the foot; weightbearing AP, mortise, and lateral views of the ankle; and the Saltzman hindfoot alignment view (long-axial hindfoot projection). Non-weightbearing films are strictly inadequate, as they underestimate dynamic mechanical collapse and joint subluxation.
• Meary’s Angle (Talar-First Metatarsal Angle, Lateral View): The angle formed between the longitudinal axis of the talus and the longitudinal axis of the first metatarsal. In a normal foot, these axes are collinear (0 ± 4 degrees). In a cavus foot, the first metatarsal angles plantarly relative to the talus, producing an apex-dorsal angulation:
  – Mild Cavus: 5 to 15 degrees apex-dorsal.
  – Moderate Cavus: 16 to 30 degrees apex-dorsal.
  – Severe Cavus: >30 degrees apex-dorsal.
• Calcaneal Pitch Angle (Lateral View): The angle subtended by the inferior cortex of the calcaneus and the horizontal ground plane. Normal reference: 18 to 24 degrees. In the cavovarus foot, calcaneal pitch increases significantly to >30 degrees, frequently reaching 35 to 45 degrees.
• Hibbs Angle (Calcaneal-First Metatarsal Angle, Lateral View): Measured between the longitudinal axis of the calcaneus and the longitudinal axis of the first metatarsal. Normal reference: 135 to 145 degrees. In cavus deformity, the angle narrows sharply to <130 degrees (often <110 degrees in severe disease).
• Lateral Talocalcaneal Angle: Formed by the intersection of the talar and calcaneal axes on the lateral projection. Normal reference: 35 to 50 degrees. In hindfoot varus, subtalar inversion causes the talus and calcaneus to become parallel, reducing the angle to <35 degrees.
• Saltzman Hindfoot Alignment View: Directly calculates the mechanical offset between the tibial shaft axis and the ground contact point of the calcaneus. Normal alignment is 2 to 6 degrees of valgus. In HMSN, the calcaneal axis shifts medially into marked varus (>5 to 15 degrees).
• Chopart Joint Line (Cyma Line) Assessment: On lateral radiographs, the continuous S-shaped cyma line formed by the talonavicular and calcaneocuboid joints is disrupted, with the talonavicular joint shifted dorsally and posteriorly relative to the calcaneocuboid joint.

Electrodiagnostic Testing & Conduction Thresholds

Nerve conduction studies (NCS) and needle electromyography (EMG) remain the primary physiologic tools for phenotypic categorization and differential diagnosis:

• Motor Nerve Conduction Velocity (MNCV) Categorization: MNCV measured in the upper extremity (median or ulnar nerve across the forearm segment) defines the neurophysiologic phenotype:
  – Demyelinating (HMSN I / CMT1): Uniform, symmetrical slowing with motor NCV <38 m/s (typically 15 to 25 m/s). Associated findings include markedly prolonged distal motor latencies (>4.5 ms) and temporally dispersed compound muscle action potentials (CMAPs). Conduction block is absent, which differentiates inherited demyelination from acquired autoimmune neuropathies (CIDP).
  – Axonal (HMSN II / CMT2): Conduction velocities remain normal or mildly slowed (>38 m/s, typically 40 to 52 m/s), but CMAP and SNAP amplitudes are markedly diminished or absent, reflecting distal axonal loss.
  – Intermediate Neuropathies: Conduction velocities fall within the intermediate range of 30 to 40 m/s. This pattern is characteristic of X-linked CMT (CMTX1 due to GJB1 mutations) and specific MPZ or DNM2 mutations.
• Needle Electromyography (EMG): Demonstrates chronic neurogenic denervation and reinnervation across distal lower extremity muscles (tibialis anterior, gastrocnemius, extensor digitorum brevis). Resting spontaneous activity includes positive sharp waves and fibrillation potentials. Voluntary recruitment reveals reduced interference patterns with high-amplitude, long-duration, polyphasic motor unit action potentials (MUAPs).

Genetic Testing Algorithms

Modern genetic diagnostics have largely replaced diagnostic sural nerve biopsy:

• Tier 1 (Targeted Duplication/Deletion Testing): Multiplex ligation-dependent probe amplification (MLPA) or targeted qPCR for the 1.4-Mb duplication on chromosome 17p11.2 (PMP22). A positive duplication confirms CMT1A, resolving more than 50% of all suspected inherited neuropathy presentations. If negative and the patient exhibits episodic focal palsies, deletion testing confirms HNPP.
• Tier 2 (Comprehensive Next-Generation Sequencing Panel): If Tier 1 is negative, perform a targeted NGS neuropathy panel covering the primary causative genes: MFN2, GJB1, MPZ, SH3TC2, GDAP1, HSPB1, NEFL, PRX, and FGD4. Multi-gene panels provide a diagnostic yield exceeding 80% in familial cases.
• Tier 3 (Whole Exome / Genome Sequencing): Indicated for complex syndromic phenotypes, early-onset recessive pedigrees, or unresolved cases following negative comprehensive gene panels.
• Role of Sural Nerve Biopsy: Nerve biopsy is invasive and carries significant risks of chronic neuroma formation and sensory deficit. It is strictly reserved for rapidly progressive, atypical, or seronegative cases to rule out treatable mimics such as amyloid polyneuropathy, vasculitic neuropathy, or atypical CIDP.

7. Classification

The clinical and electrophysiological classification established by Dyck and Harding remains the standard orthopaedic framework, now harmonized with modern molecular genetic nomenclature:

8. Treatment

Medical & Nonoperative Management

Nonoperative care is the initial management for early, flexible deformities and serves as continuous lifelong maintenance across all stages of HMSN:

• Physical Therapy & Conditioning: Focuses on low-impact aerobic conditioning (cycling, aquatic therapy) and progressive resistance training targeting preserved muscle groups (quadriceps, hamstrings, triceps surae, and tibialis posterior). Resistance training must be kept at moderate intensity; eccentric over-exertion must be avoided to prevent muscle breakdown. Daily passive stretching of the gastrocnemius-soleus complex, plantar fascia, and hamstring muscle groups is mandatory to delay fixed equinus and cavus contractures.
• Accommodative Foot Orthoses: Custom-molded orthoses are designed to neutralize the tripod effect. Key orthotic modifications include:
  – A full-length semi-rigid shell with a lateral heel wedge (3 to 5 degrees) to promote calcaneal eversion.
  – Lateral forefoot posting along the fourth and fifth metatarsals.
  – A first metatarsal head recess (“cut-out”) that allows the plantarflexed first ray to drop below the weightbearing surface, unloading the medial column and dampening the compensatory varus vector.
• Ankle-Foot Orthoses (AFOs):
  – Dynamic Carbon-Fiber AFOs: Indicated for mild-to-moderate foot drop with flexible hindfoot alignment. These lightweight, energy-storing orthoses provide swing-phase clearance, prevent toe dragging, and facilitate ground reaction push-off without restricting knee kinematics.
  – Custom Articulated or Solid AFOs: Indicated for moderate-to-severe hindfoot instability, dynamic varus thrust during stance, or fixed deformity. Fabricated with full-contact medial and lateral supramalleolar extensions to stabilize the subtalar joint and prevent recurring lateral ankle sprains.
• Strict Avoidance of Neurotoxic Medications: Clinicians, patients, and families must be provided with an explicit list of contraindicated neurotoxic pharmaceuticals:
  – Definite / High-Risk Contraindication: Vincristine is an absolute contraindication. Exposure to this vinca alkaloid in patients with underlying HMSN triggers fulminant, irreversible axonal necrosis leading to acute quadriparesis within days to weeks.
  – High-Risk Chemotherapeutic & Antimicrobial Agents: Paclitaxel, docetaxel, cisplatin, oxaliplatin, bortezomib, nitrofurantoin, amiodarone, metronidazole, and high-dose pyridoxine (Vitamin B6).
• Neuropathic Symptom Control: Musculoskeletal mechanical pain responds to activity pacing and orthotic realignment. Neuropathic dysesthesias or radicular symptoms are managed with first-line agents including gabapentinoids (gabapentin, pregabalin) or serotonin-norepinephrine reuptake inhibitors (duloxetine). Centrally sedating medications should be minimized to avoid worsening motor ataxia.
• Objective Failure Criteria: Conservative therapy is deemed to have failed when there is: (1) progressive, unbraceable deformity; (2) recurrent, disabling ankle giving-way episodes; (3) persistent plantar hyperkeratotic callosities or impending skin breakdown beneath the lateral border; or (4) intractable mechanical foot and ankle pain refractory to 6 months of supervised orthotic and physical therapy.

Operative Reconstruction

The cardinal goals of surgical intervention are to restore a plantigrade, flexible, stable, and painless foot, rebalance dynamic muscle vectors, eliminate the lateral column overload, and preserve articular joint motion whenever possible:

Joint-Preserving Surgical Algorithm (Flexible to Semi-Rigid Deformity)

In skeletally mature or maturing patients without advanced joint arthrosis whose Coleman block test demonstrates hindfoot flexibility, surgical correction follows a multi-level sequential sequence:

• Step 1: Soft-Tissue Releases & Plantar Fasciotomy:
  – Plantar Fascia Release: A complete plantar fasciotomy (open Steindler release or percutaneous release under direct palpation) is performed at the anterior-inferior calcaneal tuberosity. Releasing the contracted central and medial aponeurotic bands flattens the apex-dorsal arch and relaxes tension on the calcaneal pitch.
  – Gastrocnemius-Soleus Lengthening: Based on Silfverskiöld testing, perform an endoscopic or open gastrocnemius recession (Strayer or Vulpius technique) for isolated gastroc contracture, or a percutaneous triple-hemisection / open Z-lengthening of the Achilles tendon (TAL) for fixed gastroc-soleus equinus. Restoring at least 10 degrees of neutral ankle dorsiflexion is mandatory before completing midfoot or hindfoot osteotomies.
• Step 2: First Metatarsal Dorsiflexion Osteotomy:
  – Technique: A dorsal closing-wedge osteotomy (modified Coventry technique) of the first metatarsal base is performed 1.0 to 1.5 cm distal to the first tarsometatarsal (Lisfranc) joint. A 3- to 6-mm wedge of dorsal cortical and cancellous bone is resected, keeping the plantar cortex intact as a hinge.
  – Fixation & Objective: The osteotomy is reduced and stabilized with a low-profile dorsal titanium plate or two crossed lag screws. This elevates the first ray into neutral sagittal alignment, flattening the medial longitudinal arch and eliminating the primary medial tripod post driving hindfoot varus.
• Step 3: Tendon Transfers (Dynamic Rebalancing):
  – Peroneus Longus to Peroneus Brevis Transfer: The peroneus longus tendon is transected 2 cm proximal to the cuboid groove, and its proximal motor end is transferred side-to-side (tenodesis) or end-to-end to the tendon of the peroneus brevis. This double-benefit transfer removes the deforming plantarflexion vector on the first ray while simultaneously augmenting dynamic eversion power to counteract subtalar inversion.
  – Posterior Tibial Tendon (PTT) Transfer: The tibialis posterior tendon is harvested from its navicular insertion, routed proximally into the deep posterior compartment, and passed through a generous 4-cm window in the crural interosseous membrane into the anterior compartment. The tendon is redirected beneath the extensor retinaculum and secured into the lateral cuneiform, middle cuneiform, or cuboid using a bicortical interference screw or transosseous suture button. The transfer is tensioned with the foot held in 10 to 15 degrees of dorsiflexion and neutral eversion. This eliminates the primary deforming varus-inversion vector and restores active swing-phase dorsiflexion.
  – Jones Procedure & Claw Toe Correction: For severe cock-up hallux deformity, the extensor hallucis longus (EHL) tendon is transferred to the neck of the first metatarsal, combined with an interphalangeal (IP) joint arthrodesis. Lesser claw toes are corrected with long extensor tenotomies, PIP joint resections, and Girdlestone-Taylor flexor-to-extensor tendon transfers.
• Step 4: Calcaneal Realignment Osteotomy:
  – Lateralizing Calcaneal Osteotomy (Sliding / Translational or Dwyer Closing-Wedge): Through an oblique lateral incision, an osteotomy is performed 1.5 cm posterior to the subtalar joint at a 45-degree angle to the plantar surface. The posterior calcaneal tuberosity is translated 5 to 10 mm laterally (sliding osteotomy) or a 5- to 8-mm lateral closing wedge is excised (Dwyer technique).
  – Biomechanical Impact: Shifting the tuber laterally repositions the ground reaction force lateral to the subtalar axis, immediately converting the Achilles tendon vector from an inverter into an everter. Rigid internal fixation is achieved with one or two 6.5- to 7.3-mm cannulated cancellous screws.

Joint-Sacrificing Salvage Arthrodesis (Rigid / Arthritic Deformity)

When the Coleman block test demonstrates rigid hindfoot varus (negative test) and imaging reveals established degenerative osteoarthritis of the peritalar joints, joint preservation is no longer viable:

• Triple Arthrodesis: Consists of corrective resection of the articular cartilage and subchondral bone from the subtalar, talonavicular, and calcaneocuboid joints. Biplanar closing wedges (lateral wedge at the subtalar joint to correct varus; medial-based wedge at the Chopart complex to correct adduction and cavus) realign the hindfoot into 3 to 5 degrees of valgus. Fixation is achieved with cannulated compression screws.
• Double Arthrodesis Variant: Fuses the subtalar and talonavicular joints while intentionally sparing the calcaneocuboid joint. Sparing the lateral column reduces operative morbidity, lowers nonunion rates (which reach 10% to 15% at the CC joint in traditional triple fusions), and preserves residual lateral midfoot shock absorption while achieving comparable multiplanar deformity correction.

Indications & Contraindications

Explicit clinical and radiographic thresholds dictate the operative pathway:

• Absolute Indications for Joint-Preserving Reconstruction:
  – Symptomatic, progressive cavovarus foot with apex-dorsal Meary’s angle >10 degrees, calcaneal pitch >30 degrees, or Hibbs angle <130 degrees.
  – Coleman block test positive (flexible hindfoot varus).
  – Absence of advanced radiographic osteoarthritis across the subtalar and Chopart joints.
  – Recurrent disabling lateral ankle instability or lateral column callosities/ulcerations refractory to custom AFOs.
• Indications for Salvage Arthrodesis:
  – Fixed, rigid hindfoot varus (Coleman block test negative) in a skeletally mature adolescent or adult.
  – Severe secondary peritalar osteoarthritis (joint space narrowing, subchondral sclerosis, osteophytes).
  – Recurrent, rigid deformity following failed joint-preserving osteotomies.
• Contraindications:
  – Absolute: Active local or systemic infection; critical lower extremity limb ischemia (TcPO2 <30 mmHg); medically unstable patient unable to tolerate general anesthesia; non-ambulatory status without transfer goals.
  – Relative: Severe non-compliance with non-weightbearing protocols; Charcot neuroarthropathy active phase; donor muscle weakness (MRC grade <4 for tibialis posterior precludes successful tendon transfer); severe osteopenia precluding stable implant purchase.

9. Outcome

Patient-Reported Outcome Measures (PROMs)

Modern clinical cohorts evaluate surgical reconstruction in HMSN using validated tools, including the American Orthopaedic Foot and Ankle Society (AOFAS) Ankle-Hindfoot Scale, Foot Function Index (FFI), Visual Analog Scale (VAS) for pain, and SF-36 Health Survey:

• Joint-Preserving Reconstruction Outcomes: Multi-level joint-sparing procedures yield profound, durable improvements in functional scores. Preoperative AOFAS hindfoot scores typically average 42 to 54 points, increasing postoperatively to 78 to 88 points at intermediate follow-up (5 to 10 years). Pain scores improve significantly, with VAS pain ratings decreasing from a mean of 6.8 preoperatively to 1.8 postoperatively. Patient satisfaction rates exceed 85% to 90%, with significant improvements in physical function domains on the SF-36.
• Dynamic Gait Normalization: Computerized three-dimensional gait analysis reveals that anterior transfer of the posterior tibial tendon restores active swing-phase ankle dorsiflexion, eliminating the high-stepping steppage gait and normalizing peak ankle dorsiflexion during swing phase (from a mean of -14 degrees of plantarflexion preoperatively to +4 degrees of active dorsiflexion postoperatively). Plantar pressure mapping confirms redistribution of peak loads away from the lateral column and first metatarsal head onto the central midfoot and heel.

Survivorship: Joint Preservation vs Arthrodesis

Longitudinal survivorship profiles highlight the critical divergence between joint-preserving osteotomies and salvage arthrodesis:

• Joint Preservation Durability: Long-term follow-up studies (10 to 15 years) demonstrate an 80% to 88% survivorship of native peritalar joints without progression to secondary arthrodesis. Reoperation rates range from 12% to 18%, predominantly involving revision soft-tissue releases, secondary tendon transfers, or repeat osteotomies due to ongoing neurogenic disease progression. Importantly, preserving subtalar and transverse tarsal joint motion protects the adjacent tibiotalar joint from compensatory shear forces.
• Triple Arthrodesis Long-Term Deterioration: Although initial fusion rates are high (88% to 95%), long-term survivorship is substantially degraded by adjacent-segment degeneration:
  – Adjacent-Segment Ankle Osteoarthritis: Radiographic ankle osteoarthritis develops in 40% to 75% of patients at 15 to 30 years post-triple arthrodesis, with 25% to 35% exhibiting severe, symptomatic end-stage arthrosis requiring ankle arthrodesis or total ankle replacement.
  – Midtarsal & Naviculocuneiform Degeneration: Rigid fusion of the subtalar and Chopart joints abolishes peritalar shock absorption, transferring abnormal bending and rotational moments into the naviculocuneiform and tarsometatarsal joints, which develop radiographic arthritis in 35% to 50% of cases.

10. Complications

Surgical reconstruction of the cavovarus foot involves sensory-deficient tissues and structural bony realignment, carrying distinct intraoperative and postoperative risks:

11. Pearls and Pitfalls

Expert Surgical Pearls

• Neutralize the First Ray Driver First: The cardinal pitfall in cavovarus surgery is performing an isolated calcaneal osteotomy while failing to address a plantarflexed first ray. If the first ray remains fixed below the plane of the lesser metatarsals, the tripod effect will inevitably drive recurrent hindfoot varus. A first metatarsal dorsal closing-wedge osteotomy is essential in any patient where first ray plantarflexion persists following plantar fascia release.
• Dynamic Tendon Tensioning Benchmark: When securing the posterior tibial tendon into the lateral cuneiform, anchor the graft with the ankle held in 10 to 15 degrees of dorsiflexion and neutral eversion/inversion. Tensioning the tendon in plantarflexion results in residual dynamic foot drop, whereas tensioning in excessive valgus leads to progressive flatfoot collapse.
• Stepwise Intraoperative Re-Evaluation: Reconstruct the cavovarus foot sequentially from soft-tissue release to bony osteotomies, reassessing flexibility after each step. Perform plantar fasciotomy and gastrocnemius lengthening first; re-evaluate subtalar mobility. Perform the first metatarsal dorsiflexion osteotomy next; re-test the hindfoot with a flat board. Only proceed to calcaneal osteotomy if residual varus persists after neutralizing the forefoot driver.
• Generous Interosseous Tunnel Window: When transferring the posterior tibial tendon through the crural interosseous membrane, resect a wide, 4-cm longitudinal window in the membrane immediately lateral to the posterior tibia. A narrow slit risks scarring, tendon tethering, and compressive entrapment of the anterior tibial artery and deep peroneal nerve.
• Neurosensory Cast Protection Protocol: Because peripheral sensation is diminished or absent, all postoperative dressings and casts must be heavily padded with double-layer felt over the heel, malleoli, and fifth metatarsal tuberosity. Rigid plaster must be bivalved or split anteriorly in the operating room to accommodate post-surgical edema without skin ischemia.

Subtle Judgment Pitfalls

• Transferring a Subclinically Denervated Tendon: Never transfer the posterior tibial tendon without confirming preoperatively that its motor strength is an uncompromised MRC Grade 5. In rapidly progressive axonal variants, transferring a weakened muscle fails to provide active dorsiflexion and sacrifices medial arch support.
• Under-Recognizing Gastrocnemius Equinus: Overlooking an equinus contracture prevents true correction of the longitudinal arch and forces compensatory midfoot break. Silfverskiöld testing under general anesthesia must confirm whether gastrocnemius recession or Achilles tendon lengthening is required before joint fixation.
• The Danger of Overcorrection into Valgus: In a sensory-deficient limb, an overcorrected valgus foot is vastly more disabling and prone to breakdown than slight residual varus. Hindfoot valgus shifts weight onto the medial border, leading to rapid talonavicular subluxation, rocker-bottom collapse, and deep neuropathic ulceration. Calcaneal translation should never exceed 8 to 10 mm.
• Premature Arthrodesis in Pediatric Patients: Performing triple arthrodesis in children or young adolescents permanently locks the peritalar joints, guaranteeing premature adjacent-segment ankle osteoarthritis by early adulthood. Joint-sparing soft-tissue and osteotomy procedures must be exhausted before considering arthrodesis.

12. Controversy

Timing of Surgical Reconstruction in Pediatric Patients

The optimal timing of surgical intervention in growing children with HMSN remains an area of ongoing debate. Advocates of early proactive reconstruction recommend performing soft-tissue releases, tendon transfers, and corrective osteotomies between the ages of 6 and 12 years while deformities remain fully flexible. Early realignment prevents secondary osseous remodeling of the tarsal bones, eliminates abnormal joint contact stresses, and averts the need for salvage arthrodesis in adulthood. Conversely, opponents argue that operating on a rapidly growing skeleton carries a high risk of recurrent deformity due to relentless neurogenic disease progression, subjecting children to multiple revision surgeries. Current international consensus favors proactive joint-preserving surgery once progressive flexible cavovarus begins producing gait deterioration, recurrent sprains, or refractory callosities, avoiding joint-sacrificing fusions until after skeletal maturity.

Routing Corridor for Posterior Tibial Tendon Transfer

Surgeons remain divided regarding the optimal routing corridor for the anteriorly transferred posterior tibial tendon:

• Interosseous Membrane Route: Passing the tendon directly through a window in the interosseous membrane creates a straight-line vector of pull for dorsiflexion, eliminating angular bowstringing and providing superior mechanical efficiency. However, this route is technically demanding, risks neurovascular injury to the deep peroneal nerve and anterior tibial vessels, and carries a risk of tendon scarring within the membrane window.
• Circumtibial (Subcutaneous) Route: Rerouting the tendon anteriorly around the medial border of the tibia through the subcutaneous plane is technically straightforward, avoids deep neurovascular danger, and allows easy surgical revision. However, this path creates an oblique vector that can produce unwanted excessive inversion or eversion, and the tendon can bowstring prominently beneath the skin, causing friction irritation against footwear.

Triple versus Double Arthrodesis in Rigid Deformity

In fixed, rigid cavovarus deformity with secondary osteoarthritis, traditional triple arthrodesis (subtalar, talonavicular, and calcaneocuboid fusion) has long been the gold standard. However, clinical series have highlighted a 10% to 15% nonunion rate specifically at the calcaneocuboid (CC) joint, alongside severe lateral column rigidity. Recent comparative cohorts advocate double arthrodesis (subtalar and talonavicular fusion), intentionally sparing the CC joint. Preserving the calcaneocuboid articulation maintains physiological compliance along the lateral column, reduces nonunion risk, shortens operative duration, and achieves equivalent multi-planar correction of cavus and varus alignment without compromising clinical outcomes.

13. Evidence-Based Synthesis

Modern clinical decision-making is grounded in high-quality randomized controlled trials and prospective registry analyses, corroborated by seminal biomechanical and anatomical descriptions.

14. References

• Cesaroni CA, Caiazza L, Pisanò G et al. PMP22-Related Neuropathies: A Systematic Review. Genes (Basel). 2025. doi:10.3390/genes16111279 [Level I: Systematic Review / Meta-Analysis]
• Finsterer J, Iglseder S, Wanschitz J et al. Hereditary transthyretin-related amyloidosis. Acta Neurol Scand. 2019. doi:10.1111/ane.13035 [Level I: Systematic Review / Meta-Analysis]
• Sman AD, Hackett D, Fiatarone Singh M et al. Systematic review of exercise for Charcot-Marie-Tooth disease. J Peripher Nerv Syst. 2015. doi:10.1111/jns.12116 [Level I: Systematic Review / Meta-Analysis]
• Cavaletti G, Forsey K, Alberti P. Toxic medications in Charcot-Marie-Tooth patients: A systematic review. J Peripher Nerv Syst. 2023. doi:10.1111/jns.12566 [Level I: Systematic Review / Meta-Analysis]
• Russell JW, Windebank AJ, Harper CM Jr. Treatment of stable chronic demyelinating polyneuropathy with 3,4-diaminopyridine. Mayo Clin Proc. 1995. doi:10.4065/70.6.532 [Level I: Randomized Controlled Trial]
• Bertorini T, Narayanaswami P, Rashed H. Charcot-Marie-Tooth Disease (Hereditary Motor Sensory Neuropathies) and Hereditary Sensory and Autonomic Neuropathies. Neurologist. 2004. doi:10.1097/01.nrl.0000145596.38640.27 [Level IV: Clinical Review & Cohort Series]
• Bird TD. Hereditary Motor-Sensory Neuropathies: Charcot-Marie-Tooth Syndrome. Neurol Clin. 1989. doi:10.1016/s0733-8619(18)30825-9 [Level IV: Longitudinal Natural History Cohort]

15. Master Class Pro-Tip

Sequential realignment of the cavovarus foot in hereditary motor sensory neuropathies demands strict adherence to the inside-out algorithm: never correct the hindfoot until the forefoot driver has been fully neutralized. Begin with a comprehensive plantar fascia release and Silfverskiöld-guided gastrocnemius recession. Next, perform a dorsal closing-wedge osteotomy of the first metatarsal base, fixating the ray with a low-profile dorsal plate. Re-evaluate hindfoot alignment intraoperatively with a simulated weightbearing board: in over 70% of flexible cases, the hindfoot spontaneously reduces to neutral valgus once the rigid medial tripod post is elevated. Only if persistent varus remains should a lateralizing calcaneal osteotomy (Dwyer or translational sliding) be executed, translating the tuberosity no more than 8 to 10 mm. When performing the posterior tibial tendon transfer, route the tendon through a wide, 4-cm interosseous window and anchor it to the lateral cuneiform with the ankle held in 10 degrees of dorsiflexion and neutral rotation—over-tensioning into valgus in a sensory-deficient limb risks rapid, catastrophic medial column breakdown that is exponentially more debilitating than mild residual varus.

Master Class Surgical Pearl: Realignment of the Cavovarus Foot in Hereditary Motor Sensory Neuropathies