Cavovarus Foot

1. Clinical Overview

Summary

The cavovarus foot is a complex three-dimensional deformity characterized by a pathologically elevated longitudinal arch (cavus), hindfoot varus angulation, and forefoot adduction. Unlike the more common and often benign flatfoot deformity, cavovarus foot is almost always pathological and represents an underlying neuromuscular imbalance in approximately 70% of cases. [1,2]

The deformity creates a rigid, tripod-like foot structure that overloads the lateral border (particularly the 5th metatarsal base) and places excessive strain on lateral ankle ligaments, predisposing to recurrent ankle sprains and progressive lateral column pathology. The mechanical inefficiency of the cavovarus foot results in early fatigue, pain, instability, and eventual degenerative changes if left untreated. [3,4]

Charcot-Marie-Tooth disease (CMT), the most common inherited peripheral neuropathy with a prevalence of 1 in 2,500, accounts for approximately one-third to two-thirds of all cavovarus feet. The remaining cases are distributed among other neurologic conditions (spinal cord pathology, cerebral palsy, poliomyelitis sequelae) and truly idiopathic presentations. [5,6] The key clinical principle is that cavovarus deformity is progressive and driven by muscular imbalance: stronger motors (peroneus longus, tibialis posterior) overpower weakened antagonists (tibialis anterior, peroneus brevis), twisting the foot into its characteristic configuration. [7]

Early recognition and systematic evaluation are critical. The Coleman block test remains the cornerstone clinical examination maneuver to differentiate forefoot-driven flexible deformities (amenable to soft tissue procedures and limited osteotomies) from fixed hindfoot deformities (requiring more extensive bony reconstruction). [8] Treatment philosophy has evolved from early arthrodesis to joint-preserving reconstruction whenever possible, aiming to rebalance muscular forces and realign skeletal architecture before irreversible arthritis supervenes. [9,10]

Key Facts

The Rule of Thirds (Aetiology Distribution)

• 33-66% have Charcot-Marie-Tooth disease (CMT1A most common subtype)
• 20-33% have other neurologic causes (spinal dysraphism, cord tumor, cerebral palsy, stroke, polio sequelae)
• 10-30% are labeled idiopathic (subtle cavus, familial, no identifiable neurologic disease)
• Critical Point: Nearly 70% of high-arched feet have an underlying neurologic aetiology requiring systematic workup. [1,5,11]

Forefoot-Driven Deformity Mechanism In the majority of cavovarus feet, the deformity originates in the forefoot. Unopposed peroneus longus activity (relative to weak tibialis anterior) plantarflexes the first ray. To achieve plantigrade foot contact during stance, the hindfoot compensates by rotating into varus. This "forefoot-driven hindfoot varus" is the fundamental biomechanical principle underlying most cavovarus deformities. [12,13]

The Coleman Block Test This single examination maneuver determines surgical planning. A 1-inch (2.5 cm) wooden block is placed under the heel and lateral foot, allowing the plantarflexed first ray to drop freely. If the hindfoot corrects from varus to neutral or valgus, the deformity is forefoot-driven and flexible—correctable with first metatarsal osteotomy and soft tissue balancing. If the hindfoot remains fixed in varus despite eliminating forefoot deforming forces, primary hindfoot pathology exists requiring calcaneal osteotomy. [8,14]

Clinical Pearls

"Peek-a-Boo Heel Sign": When examining the standing patient from the anterior aspect, visualization of the medial border of the heel lateral to the tibia indicates severe hindfoot varus. This sign correlates with lateral ankle instability and lateral column overload. [15]

"Unilateral = Spinal": Any patient presenting with unilateral high-arched foot requires urgent whole-spine MRI to exclude intraspinal pathology (syrinx, ependymoma, lipoma, tethered cord). CMT and hereditary neuropathies are bilateral; unilateral presentations are neurogenic until proven otherwise. [16]

"The Tripod Analogy": Visualize the foot as a three-point support system: heel, first metatarsal head, fifth metatarsal head. If the first metatarsal "leg" is too long (plantarflexed), the tripod tilts laterally. Shortening (dorsiflexion osteotomy) or weakening the first ray (plantar fascia release, peroneus longus transfer) levels the tripod. [17]

"Address the Cause, Not Just the Deformity": Surgical correction without addressing progressive neuromuscular imbalance will fail. In CMT patients, deformity may recur if performed too early before muscle imbalance plateaus (typically late adolescence). Consider the natural history of the underlying condition when timing reconstruction. [18]

---

2. Epidemiology

Demographics

Age Distribution

• Presentation: Most commonly recognized in adolescence (ages 10-16) as CMT phenotype manifests and deformity becomes symptomatic
• Adult presentation: Later diagnosis in mild cases or slowly progressive forms; may present in 3rd-4th decade with pain and instability rather than cosmetic concerns
• Paediatric onset: Congenital cavus (rare) suggests arthrogryposis or congenital vertical talus; acquired cavus before age 3-5 warrants urgent neurologic investigation [19]

Sex Distribution

• No significant sex predilection for cavovarus deformity overall
• CMT1A (most common subtype): equal male-female distribution
• CMT1X: X-linked inheritance pattern with more severe phenotype in males [5]

Genetic Factors

• Charcot-Marie-Tooth disease: Autosomal dominant inheritance in 70% (CMT1A, duplication of PMP22 gene on chromosome 17p11.2), autosomal recessive in 20%, X-linked in 10%
• Penetrance is high but phenotypic expression variable; family members may have minimal foot deformity despite carrying the mutation
• Hereditary motor sensory neuropathy classification: CMT1 (demyelinating, slower nerve conduction) vs CMT2 (axonal, preserved conduction velocity) [6,20]

Aetiology

Neuromuscular Causes (65-70%)

Peripheral Nerve Disorders

• Charcot-Marie-Tooth disease: 33-66% of all cavovarus feet
• Hereditary sensory and autonomic neuropathies (HSAN)
• Dejerine-Sottas disease (CMT3)
• Roussy-Levy syndrome

Spinal Cord Pathology

• Spina bifida occulta with tethered cord
• Syringomyelia
• Intraspinal tumors: Ependymoma, lipoma, dermoid cyst
• Spinal cord injury: Post-traumatic, compartment syndrome sequelae

Central Nervous System Disorders

• Cerebral palsy: Hemiplegia with equinovarus component
• Stroke: Hemiparetic foot deformity
• Spinal muscular atrophy
• Friedreich's ataxia: Progressive spinocerebellar degeneration

Anterior Horn Cell Disease

• Poliomyelitis: Now rare in developed countries but significant historical cause
• Post-polio syndrome: Late progression decades after initial infection

Idiopathic Cavus (15-30%)

• No identifiable neurologic, genetic, or traumatic aetiology despite thorough investigation
• Often familial with milder phenotype
• May represent undiagnosed subtle neuropathy or polygenic inheritance pattern
• Generally non-progressive or slowly progressive [11]

Post-Traumatic (less than 5%)

• Compartment syndrome sequelae: Volkmann's ischaemic contracture of foot
• Malunited calcaneal fracture with varus malposition
• Crush injury with selective muscle group damage

Residual Congenital Deformity (less than 5%)

• Under-corrected or relapsed clubfoot (talipes equinovarus)
• Congenital vertical talus with secondary changes
• Arthrogryposis multiplex congenita

Prevalence and Incidence

Precise epidemiologic data for cavovarus foot are limited due to heterogeneous aetiology and varying definitions. Estimates suggest:

• Overall prevalence: 10-15% of the population has some degree of elevated arch, but true symptomatic pathological cavus affects less than 1-2%
• CMT prevalence: 1 in 2,500 (40 per 100,000), with foot deformity present in 50-90% of affected individuals depending on disease duration and severity [5]
• Bilateral presentation: 85-90% of neuromuscular causes present bilaterally
• Unilateral presentation: less than 10%, strongly suggests focal spinal cord pathology [16]

---

3. Pathophysiology

Muscular Imbalance: The Central Mechanism

The cavovarus deformity develops from chronic muscular imbalance around the foot and ankle. In CMT and most other neuropathies, the pattern follows the "anterior-lateral weakness, posterior-medial preservation" rule. [7,21]

Weakened Muscle Groups

1. Tibialis Anterior: Primary ankle dorsiflexor

   • Loss of dorsiflexion power leads to foot drop and compensatory recruitment of toe extensors
   • Inability to counteract peroneus longus plantarflexion of first ray

2. Peroneus Brevis: Foot evertor and lateral stabilizer

   • Weakness allows unopposed tibialis posterior inversion
   • Contributes to hindfoot varus and lateral ankle instability

3. Intrinsic Foot Muscles: Lumbricals and interossei

   • Atrophy causes loss of metatarsophalangeal (MTP) flexion and interphalangeal (IP) extension
   • Results in claw toe deformity (MTP hyperextension, IP flexion)
   • Extensor substitution pattern emerges

Preserved or Relatively Strong Muscle Groups

1. Peroneus Longus: Plantarflexor of first ray, foot evertor

   • Insertion on base of first metatarsal and medial cuneiform
   • Unopposed action pulls first ray into plantarflexion, creating cavus arch
   • The SINGLE most important deforming force in most cavovarus feet [12]

2. Tibialis Posterior: Primary invertor, hindfoot stabilizer

   • Overpowers weak peroneus brevis
   • Pulls hindfoot into varus
   • May contribute to forefoot adduction

3. Gastrocnemius-Soleus Complex: Often preserved initially

   • Can contribute to equinus component in severe cases
   • Achilles contracture develops secondarily from chronic forefoot plantarflexion

Biomechanical Cascade

Stage 1: Forefoot Plantarflexion

• Peroneus longus overpull plantarflexes first ray
• Medial forefoot sits lower than lateral forefoot
• First metatarsal-ground contact forces forefoot into pronation relative to hindfoot

Stage 2: Compensatory Hindfoot Varus

• To achieve stable tripod foot contact (heel, 1st MT, 5th MT), hindfoot must supinate
• Calcaneus inverts and adducts relative to talus (subtalar varus)
• Ankle joint axis shifts medially, increasing varus moment arm [13]

Stage 3: Claw Toe Development

• Weak tibialis anterior recruits extensor digitorum longus (EDL) and extensor hallucis longus (EHL) as dorsiflexion substitutes
• Chronic EDL/EHL overactivity extends MTPs
• Weak intrinsics allow IP joints to flex
• Classic claw toe deformity (MTP extension, PIP/DIP flexion) [22]

Stage 4: Bony Remodeling and Fixed Deformity

• Chronic abnormal forces remodel growing skeleton in adolescents
• Talar neck deviates medially
• Calcaneal pitch increases (> 30 degrees)
• Midfoot develops fixed cavus as Lisfranc and midtarsal joints stiffen
• Articular cartilage damage begins, particularly lateral ankle and subtalar joint [23]

Three-Dimensional Deformity Components

Sagittal Plane

• Cavus: Increased longitudinal arch height
• Forefoot plantarflexion: First ray most affected
• Calcaneal pitch increase: Heel bone more vertical (normal 15-20°, cavus > 30°)

Coronal Plane

• Hindfoot varus: Calcaneal inversion relative to tibial axis
• Forefoot valgus: Pronation of forefoot relative to rearfoot
• Ankle varus tilt: Chronic lateral ligament laxity allows lateral talar tilt

Transverse Plane

• Forefoot adduction: Midfoot medial deviation
• Subtalar rotation: External rotation of heel relative to tibia
• Tibial torsional changes: Compensatory external tibial torsion may develop

Pathologic Consequences

Lateral Column Overload

• Fifth metatarsal base stress fractures (Jones fractures common)
• Lateral midfoot pain and arthritis
• Cuboid syndrome (painful cuboid subluxation) [4]

Lateral Ankle Instability

• Chronic inversion stress overloads anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL)
• Recurrent ankle sprains (85% of cavovarus patients report history of "weak ankles")
• Progressive lateral ligament attenuation and possible ankle arthritis [15]

Plantar Fascia Contracture

• "Windlass mechanism" maintains arch height through plantar fascial tension
• Chronic tightness exacerbates cavus and causes plantar heel pain
• Plantar fascia release is often a key component of surgical reconstruction [24]

Claw Toe Sequelae

• Dorsal MTP pain from shoe pressure on prominent joints
• Plantar metatarsalgia from loss of fat pad protection
• Nail dystrophy and corns at IP joints
• Painful calluses under metatarsal heads

---

4. Clinical Presentation

Symptoms

Pain Patterns

• Lateral foot pain: Most common presenting symptom (60-70% of patients)

  • Fifth metatarsal base overload
  • Lateral midfoot stress
  • Peroneal tendon irritation

• Plantar pain:

  • Metatarsalgia under 1st and 5th MT heads (callus formation common)
  • Plantar fasciitis-type heel pain from chronic fascial tension

• Ankle pain:

  • Lateral ankle discomfort from chronic instability
  • Sinus tarsi syndrome from subtalar joint irritation

• Dorsal foot pain:

  • Claw toe MTP joint prominence rubbing in shoes
  • Dorsal midfoot stress from hypermobile compensatory mechanisms

Functional Limitations

• Recurrent ankle sprains: 80-90% of symptomatic patients report multiple ankle inversion injuries
• Instability sensation: "My ankle gives out" on uneven ground
• Clumsiness and tripping: Foot drop from weak tibialis anterior causes toe-catch during swing phase
• Footwear difficulties: Inability to fit standard shoes due to high arch and claw toes
• Activity limitation: Pain with prolonged standing, walking, and athletic activities

Progression Indicators

• Increasing deformity: Worsening arch height, more prominent heel varus
• Worsening pain: Transition from activity-related to constant pain suggests arthritis development
• Stiffness: Loss of flexibility indicates fixed bony deformity and joint deterioration
• Proximal symptoms: Knee and hip pain from compensatory gait abnormalities; back pain from altered posture [25]

Signs

Inspection (Standing)

• Cavus arch: Daylight visible under medial longitudinal arch when standing
• Hindfoot varus: Calcaneal inclination medially
• Peek-a-boo heel sign: Medial heel border visible from anterior view
• Forefoot abduction: "Too many toes sign" (> 2 toes visible lateral to heel from behind suggests valgus, but absent in cavovarus)
• Calf atrophy: "Stork leg" or "inverted champagne bottle" appearance in CMT (distal leg atrophy with preserved proximal bulk)
• Claw toes: MTP hyperextension, IP flexion
• Calluses: Plantar first and fifth MT heads, lateral border of foot

Inspection (Walking)

• Foot drop: Toe-ground contact during swing phase, requires hip and knee hyperflexion compensation (steppage gait)
• Inversion bias: Heel strike occurs on lateral border
• Circumduction: Swing phase circumduction to clear toes
• Reduced push-off: Weak gastrocnemius-soleus or painful forefoot limits terminal stance power [21]

Palpation

• Tenderness: Lateral column (5th MT base), plantar fascia insertion, lateral ankle ligaments, dorsal MTP joints
• Muscle bulk: Assess calf, anterior compartment, and intrinsic foot muscle volume
• Pulses: Ensure adequate vascular supply (peripheral neuropathy may coexist with vascular disease in older patients)

Range of Motion Assessment

• Ankle dorsiflexion: Often limited (equinus contracture); measure with knee flexed (gastrocnemius relaxed) and extended
• Subtalar motion: Reduced inversion-eversion range, fixed in inverted position
• First ray mobility: Assess flexibility of first tarsometatarsal joint (hypermobile vs fixed plantarflexion)
• MTP/IP flexibility: Determine if claw toes are flexible (passively correctable) or fixed (require bony procedures)

The Coleman Block Test (CRITICAL)

1. Setup: Patient stands with lateral heel and foot on 2.5cm wooden block, first ray hanging free medially
2. Observation: Examine hindfoot alignment from behind
3. Interpretation:
   • Positive (flexible): Hindfoot corrects from varus to neutral or valgus → forefoot-driven deformity, amenable to first MT osteotomy and soft tissue balancing
   • Negative (rigid): Hindfoot remains in varus → fixed hindfoot deformity requires calcaneal osteotomy
4. Surgical Planning: Single most important test for determining operative strategy [8,14]

Neurologic Examination (MANDATORY)

• Motor strength: Test all major muscle groups in foot and ankle (graded 0-5 MRC scale)
  • Tibialis anterior (ankle dorsiflexion)
  • Extensor hallucis longus (great toe extension)
  • Extensor digitorum longus (lesser toe extension)
  • Peroneus longus and brevis (ankle eversion)
  • Tibialis posterior (ankle inversion)
  • Gastrocnemius-soleus (ankle plantarflexion)
• Sensory testing: Light touch, pinprick, vibration (128 Hz tuning fork), proprioception in "stocking" distribution
• Reflexes: Achilles and patellar tendon reflexes (reduced or absent in CMT)
• Proximal examination: Hand intrinsic wasting (CMT affects hands later than feet), proximal weakness, scoliosis (Friedreich's ataxia, syrinx)
• Cerebellar signs: Ataxia, dysmetria, nystagmus (Friedreich's ataxia) [6]

Special Tests

• Ankle anterior drawer: Assess ATFL integrity (chronic instability common)
• Ankle talar tilt: Assess CFL integrity
• Silfverskiöld test: Differentiate gastrocnemius vs gastrocnemius-soleus contracture (dorsiflexion with knee extended vs flexed)
• Windlass test: Passive great toe dorsiflexion tightens plantar fascia and raises arch (demonstrates plantar fascia contribution to cavus)

---

5. Differential Diagnosis

Primary Differentials

1. Clubfoot (Talipes Equinovarus) - Residual or Recurrent

• Distinguishing features: History of treatment in infancy, more severe equinus component, midfoot bean-shaped appearance, medial crease
• Age: Presents in infancy, but under-treated cases persist into adulthood
• Imaging: Talus-calcaneus parallelism on AP radiograph (both bones aligned rather than diverging)

2. Post-Traumatic Foot Deformity

• Distinguishing features: Clear trauma history (calcaneal fracture, compartment syndrome, Lisfranc injury)
• Timing: Acute onset following injury rather than insidious progression
• Pattern: Often unilateral; deformity corresponds to injury site

3. Isolated Plantar Fasciitis with High Arch

• Distinguishing features: Pain isolated to plantar heel, no hindfoot varus, no neurologic findings
• Age: Typically 40-60 years, degenerative process
• Response to treatment: Improves with conservative measures (stretching, orthotics, corticosteroid injection)

4. Posterior Tibial Tendon Dysfunction (PTTD) - Opposite Deformity

• Distinguishing features: Flatfoot (planovalgus) rather than cavovarus; "too many toes sign" present
• Mechanism: PTT failure causes loss of arch support (opposite to cavovarus)
• Useful for contrast: Helps reinforce cavovarus pathomechanics

5. Congenital Vertical Talus

• Distinguishing features: "Rocker-bottom" foot, rigid dorsal dislocation of navicular on talus
• Age: Presents in infancy
• Associated conditions: Often syndromic (arthrogryposis, myelomeningocele)

Underlying Aetiologies to Rule Out

When Unilateral Presentation

• Spinal cord tumor: Ependymoma, astrocytoma, lipoma (URGENT MRI spine required)
• Syringomyelia: Post-traumatic or associated with Chiari malformation
• Tethered cord: Spina bifida occulta with progressive neurologic deficit
• Stroke/hemiplegia: Spastic hemiplegic cavovarus (CNS upper motor neuron pattern)

When Bilateral Presentation

• Charcot-Marie-Tooth disease: Most common; family history, sensory loss, distal atrophy
• Friedreich's ataxia: Ataxia, dysarthria, cardiomyopathy, pes cavus in 80-90%
• Cerebral palsy: Diplegia with equinovarus components; non-progressive from birth injury
• Spinal muscular atrophy: Proximal weakness, hypotonia, anterior horn cell degeneration

---

6. Investigations

Imaging

Weight-Bearing Radiographs (ESSENTIAL)

Lateral View - Key Measurements

1. Calcaneal Pitch Angle: Angle between inferior calcaneus and floor

   • Normal: 15-25 degrees
   • Cavus: > 30 degrees (indicates elevated hindfoot)

2. Meary's Angle (Talus-First Metatarsal Angle): Long axis of talus to long axis of first metatarsal

   • Normal: 0 ± 5 degrees (aligned)
   • Cavus: Apex plantar angle > 10 degrees (downward angulation indicates midfoot break and first ray plantarflexion) [26]

3. Hibbs Angle (Talocalcaneal Angle): Angle between talus and calcaneus long axes

   • Normal: 25-50 degrees
   • Cavus: less than 20 degrees (parallel bones indicate hindfoot cavus)

4. Lateral Talometatarsal Angle: Dorsal angulation > 15 degrees indicates forefoot plantarflexion

AP (Anteroposterior) View - Key Measurements

1. AP Talocalcaneal Angle (Kite's Angle): Divergence of talus and calcaneus

   • Normal: 20-40 degrees
   • Cavus: less than 15 degrees (parallel bones indicate varus)

2. Talonavicular Coverage: Lateral uncovering suggests hindfoot varus

3. Metatarsal Break: Check for abnormal alignment or arthritis at tarsometatarsal joints

Additional Radiographic Findings

• Fifth metatarsal base: Stress fracture, sclerosis, or hypertrophy from chronic overload
• Ankle joint: Lateral talar tilt (chronic lateral ligament laxity)
• Arthritis: Joint space narrowing, subchondral sclerosis, osteophytes (subtalar, midtarsal, ankle) [27]

Advanced Imaging

MRI Spine (If Unilateral or Rapid Progression)

• Indication: Rule out intraspinal pathology (syrinx, tumor, tethered cord)
• Protocol: Whole spine T1 and T2 sequences, sagittal and axial views
• Findings to identify: Cord expansion (tumor, syrinx), tethered cord, spina bifida occulta, intraspinal lipoma [16]

MRI Foot and Ankle (Selected Cases)

• Indications:
  • Suspected peroneal tendon pathology (tears, subluxation)
  • Lateral ligament assessment prior to reconstruction
  • Osteochondral lesions of talus
  • Soft tissue masses
• Findings: Tendon tears, ligament attenuation, bone marrow edema (stress response), cartilage defects

CT Scan (Pre-operative Planning)

• Indications: Severe deformity requiring complex reconstruction, arthritis assessment, malunion evaluation
• Advantages: Superior bony detail for osteotomy planning, 3D reconstruction capabilities
• Use: Increasingly utilized for patient-specific instrumentation and 3D printed models [28]

Neurophysiology

Nerve Conduction Studies (NCS) and Electromyography (EMG)

• Indication: All patients with suspected neuromuscular aetiology

• Purpose:

  • Confirm peripheral neuropathy
  • Differentiate demyelinating (CMT1, slow conduction) vs axonal (CMT2, preserved conduction) types
  • Assess severity and distribution
  • Guide genetic testing (CMT1A vs other subtypes)

• Typical CMT1A Findings:

  • "Motor nerve conduction velocity: less than 38 m/s (markedly reduced, normal > 50 m/s)"
  • "Sensory nerve action potentials: Reduced or absent amplitude"
  • "Distal latencies: Prolonged"
  • "Chronic denervation on EMG: Fibrillations, positive sharp waves, reduced recruitment [6]"

Genetic Testing

Indications

• Confirmed peripheral neuropathy on NCS/EMG
• Family history of CMT or similar foot deformities
• Bilateral progressive cavovarus without alternative explanation

First-Line Test

• PMP22 duplication testing: Detects CMT1A (70% of CMT1 cases)
• Method: Multiplex ligation-dependent probe amplification (MLPA) or fluorescence in situ hybridization (FISH)

Extended Panel (if PMP22 negative)

• CMT gene panel (> 100 genes identified): MPZ, GJB1 (connexin-32), MFN2, GDAP1, others
• Whole exome sequencing for atypical presentations [5]

Laboratory Tests

Basic Workup (rule out acquired neuropathy)

• Complete blood count (CBC): Anemia, vitamin B12 deficiency
• Metabolic panel: Diabetes, renal function
• Thyroid function: Hypothyroidism
• Vitamin B12, folate levels
• HbA1 c: Diabetic neuropathy (unlikely to cause isolated cavovarus but assess if other risk factors)

Specialized Tests (based on clinical suspicion)

• Creatine kinase: Muscular dystrophy
• Very long chain fatty acids: Adrenoleukodystrophy
• Genetic testing: Friedreich's ataxia (frataxin gene trinucleotide repeat expansion)

Functional Assessment

Gait Analysis (Specialized centers)

• Indications: Complex cases, surgical planning in ambulatory patients with neuromuscular disease
• Parameters: Ground reaction forces, temporal-spatial parameters, kinetics, kinematics
• Findings: Lateral weight-bearing bias, reduced push-off power, toe-drag during swing [29]

Pedobarography (Plantar Pressure Mapping)

• Purpose: Quantify lateral column overload, first and fifth MT head pressures
• Application: Document pre-operative pathology, assess post-operative correction
• Findings: Elevated lateral column pressures, absence of medial arch contact, increased MT head loading [30]

---

7. Classification and Staging

Anatomical Classification (DeVries and Mizel)

Type 1: Mild Flexible

• Coleman block test positive (heel corrects)
• Forefoot-driven
• Passively correctable claw toes
• No arthritis
• Treatment: Soft tissue procedures, first MT osteotomy

Type 2: Moderate Rigid

• Coleman block test negative (heel stays in varus)
• Fixed hindfoot component
• Fixed claw toes
• Early arthritis
• Treatment: Calcaneal osteotomy, midfoot osteotomies, possible fusions

Type 3: Severe Arthritic

• Rigid deformity
• Established arthritis (subtalar, midtarsal, or ankle)
• Fixed soft tissues
• Treatment: Arthrodesis (triple arthrodesis or talocalcaneal fusion)

Pathophysiology-Based Classification

Forefoot-Driven Cavovarus (Most common)

• Primary deformity: First ray plantarflexion
• Compensatory: Hindfoot varus
• Coleman block test: Positive (corrects)
• Surgery targets: First MT, plantar fascia, peroneus longus

Hindfoot-Driven Cavovarus (Less common)

• Primary deformity: Hindfoot varus (tibialis posterior overactivity, congenital)
• Compensatory: Forefoot supination
• Coleman block test: Negative (fixed)
• Surgery targets: Calcaneal osteotomy, posterior tibial tendon

Combined Pattern (Severe cases)

• Both forefoot and hindfoot components fixed
• Coleman block test: Negative
• Surgery targets: Both first MT and calcaneal osteotomies

Functional Classification

Grade 1: Asymptomatic

• Deformity present but no pain or functional limitation
• May require only observation and orthotic management

Grade 2: Symptomatic - Non-Arthritic

• Pain, instability, or activity limitation
• No radiographic arthritis
• Joint-preserving reconstruction indicated

Grade 3: Symptomatic - Arthritic

• Pain with established degenerative changes
• Stiffness and reduced ROM
• Arthrodesis procedures required [31]

---

8. Management

Conservative Management

Indications

• Mild, asymptomatic deformity
• Patient declines surgery
• Poor surgical candidate (medical comorbidities, vascular insufficiency)
• Progressive neuromuscular disease (stabilize before definitive reconstruction)

Orthotic Management

Custom Foot Orthoses

• Lateral wedge: 3-5mm lateral heel wedge to push hindfoot out of varus (only effective if some flexibility remains)
• First metatarsal recess: Accommodate plantarflexed first ray, reduce plantar pressure
• Total contact design: Distribute pressures, support medial arch
• Metatarsal pad: Proximal to MT heads to offload forefoot pain
• Limitations: Cannot correct fixed deformity; provides symptom relief only [32]

Ankle-Foot Orthosis (AFO)

• Indication: Significant foot drop, ankle instability
• Types:
  • "Hinged AFO: Allows plantarflexion, blocks dorsiflexion (prevents drop)"
  • "Carbon fiber AFO: Lightweight, dynamic response"
  • "Custom molded AFO: Maximum control for severe deformity"
• Benefits: Improves gait efficiency, prevents tripping, reduces ankle sprains

Footwear Modifications

• High-toe-box shoes: Accommodate claw toes
• Wide forefoot: Reduce lateral border compression
• Cushioned insoles: Shock absorption
• Lateral flare: Increases lateral stability
• Lace-up or Velcro closure: Better accommodation of high arch

Physical Therapy

• Stretching: Plantar fascia, Achilles tendon, toe flexors (maintain flexibility)
• Strengthening: Tibialis anterior (foot dorsiflexion), intrinsic foot muscles (if possible)
• Proprioception training: Balance exercises to reduce ankle sprains
• Gait training: Optimize compensatory mechanisms, improve efficiency [33]

Activity Modification

• Avoid high-impact activities if painful
• Low-impact alternatives: Swimming, cycling
• Gradual return to activity after acute exacerbations

Pharmacologic

• NSAIDs: Acute pain flares (use cautiously with renal monitoring)
• Neuropathic pain medications: Gabapentin, pregabalin for painful neuropathy (CMT patients may have painful variant)

Failure of Conservative Treatment indicates surgery:

• Progressive pain despite 6 months of appropriate conservative management
• Recurrent ankle sprains with functional instability
• Worsening deformity with shoe-fitting difficulties
• Stress fractures or arthritis development

Surgical Management

Principles of Reconstruction

1. Restore plantigrade foot: Eliminate varus, achieve neutral hindfoot alignment
2. Balance muscular forces: Transfer or weaken deforming motors, strengthen weak motors
3. Preserve joints when possible: Avoid fusion in younger patients if feasible
4. Address all components: Forefoot, hindfoot, and claw toes must all be corrected
5. Customize procedure: "À la carte" approach based on flexibility, fixed vs flexible, patient age [9,10]

Pre-operative Planning

• Review Coleman block test results (determines calcaneal osteotomy need)
• Assess claw toe flexibility (determines soft tissue vs bony correction)
• Document neurologic status (progressive disease may influence timing)
• Radiographic templating for osteotomies
• Patient counseling: realistic expectations, prolonged rehabilitation (6-12 months), possible need for staged procedures

Soft Tissue Procedures

1. Plantar Fascia Release (Steindler Stripping)

• Indication: Almost all cavovarus reconstructions
• Technique:
  • Medial approach at origin on medial calcaneal tubercle
  • Release plantar fascia, abductor hallucis origin, short toe flexors from calcaneus
  • Incomplete release (preserve lateral 1/3) to avoid excessive flattening
• Effect: Releases "windlass mechanism," allows arch to flatten
• Outcomes: Reduces pain, decreases cavus by average 5-10 degrees Meary angle [24]

2. Peroneus Longus to Brevis Transfer (PL to PB)

• Indication: Forefoot-driven cavovarus with weak eversion
• Rationale: Eliminates first ray plantarflexion force, augments eversion power
• Technique:
  • Detach PL tendon from base of first MT/medial cuneiform
  • Reroute and suture to PB tendon at lateral foot
  • "Alternative: Intramuscular lengthening of PL"
• Effect: Removes deforming force, strengthens lateral stabilizers
• Caution: Ensure adequate PB strength to accept transfer [7]

3. Jones Procedure (EHL Transfer + IP Fusion)

• Indication: Flexible claw hallux with weak ankle dorsiflexion (foot drop)
• Technique:
  • Detach extensor hallucis longus tendon from distal phalanx
  • Transfer to first metatarsal neck or midshaft
  • Fuse IP joint of great toe (prevent floppy toe)
  • Fix with Kirschner wire or screw
• Effect:
  • Removes MTP extension deforming force (corrects claw toe)
  • Provides active ankle dorsiflexion (treats drop foot)
• Outcomes: Improves gait, reduces tripping, maintains hallux position [34]

4. Claw Toe Correction

Flexible Claw Toes

• Flexor to extensor transfer (Girdlestone-Taylor):
  • Transfer flexor digitorum longus (FDL) to extensor hood dorsally
  • Corrects flexible MTP hyperextension and IP flexion
  • Preserves MTP joint mobility

Fixed Claw Toes

• Proximal interphalangeal (PIP) fusion: Arthrodesis in corrected position
• Metatarsal osteotomy (Weil): Shorten metatarsal to relax extensor mechanism
• MTP fusion (severe): Reserved for arthritic or severely rigid deformities

5. Achilles Tendon Lengthening

• Indication: Equinus contracture (dorsiflexion less than 10° with knee extended)
• Techniques:
  • "Triple hemisection: Three percutaneous cuts (medial proximal, lateral middle, medial distal) with controlled lengthening"
  • "Z-plasty: Open lengthening with anatomic repair"
• Goal: Achieve 10-15 degrees dorsiflexion with knee extended [35]

Bony Procedures (Osteotomies)

1. First Metatarsal Dorsiflexion Osteotomy

• Indication: Forefoot-driven cavovarus (positive Coleman block test)
• Rationale: Elevates plantarflexed first ray, eliminates tripod imbalance
• Technique:
  • Dorsal closing wedge osteotomy at base or midshaft of first MT
  • Remove 3-5mm dorsal wedge
  • Fix with plate or dorsal screws
  • Elevates first MT by 5-10mm typically
• Effect: Corrects forefoot pronation, allows hindfoot to derotate out of varus
• Outcomes: Successful correction in 75-85% when combined with soft tissue releases [36]

2. Calcaneal Osteotomy (Dwyer Lateralizing Osteotomy)

• Indication: Fixed hindfoot varus (negative Coleman block test)
• Rationale: Shifts heel laterally, corrects varus alignment, decreases lateral ankle strain
• Technique:
  • Lateral closing wedge through posterior calcaneus (Dwyer)
  • Remove 5-10mm lateral-based wedge
  • Fix with staples or screws
  • "Alternative: Z-osteotomy for more severe deformity (allows lateral translation and lengthening)"
• Amount of correction: 5-7mm wedge corrects ~10 degrees varus
• Effect: Shifts weight-bearing axis medially, reduces lateral column overload
• Outcomes: 80-90% good/excellent results in appropriate cases [37]

3. Midfoot Osteotomies (Cole Osteotomy)

• Indication: Severe midfoot cavus (apex of deformity at midfoot rather than forefoot/hindfoot)
• Technique:
  • Dorsal closing wedge through midtarsal joints (naviculocuneiform, tarsometatarsal)
  • Removes bone from dorsal midfoot to flatten arch
  • Plate fixation
• Less commonly performed: Risk of midfoot stiffness, complex healing
• Reserved for: Severe rigid midfoot cavus unresponsive to forefoot/hindfoot procedures [38]

4. Triple Arthrodesis

• Indication:
  • Rigid deformity with established arthritis
  • Failed previous reconstruction
  • Severe neuromuscular disease with minimal ambulatory potential
  • Salvage procedure
• Joints fused: Subtalar, talonavicular, calcaneocuboid
• Goals:
  • Rigid plantigrade foot
  • Pain relief from arthritic joints
  • Stable platform for ambulation
• Technique:
  • Correct all three planes of deformity simultaneously
  • Achieve hindfoot neutral (0-5 degrees valgus), plantigrade forefoot
  • Multiple incisions (medial, lateral) or single extensile lateral incision
  • Bone graft often needed
  • Rigid internal fixation (screws, plates)
• Outcomes:
  • 70-85% patient satisfaction
  • Pain relief in 80-90%
  • Non-union risk 5-15% (higher with smoking, diabetes, neuromuscular disease)
  • Adjacent joint arthritis (ankle, midfoot) in 25-40% long-term [39,40]
• Complications: Non-union, malunion, adjacent joint arthritis, limb length discrepancy, stiffness

Surgical Algorithm

CAVOVARUS FOOT
       ↓
COLEMAN BLOCK TEST
       ↓
    ┌──────────────────┴──────────────────┐
    ↓                                     ↓
POSITIVE (Corrects)              NEGATIVE (Fixed Hindfoot)
Forefoot-Driven                  Hindfoot Component
    ↓                                     ↓
SOFT TISSUE BALANCING:           CALCANEAL OSTEOTOMY
• Plantar fascia release         (Dwyer/Z-osteotomy)
• PL to PB transfer                      +
• Jones procedure (if drop foot)  SOFT TISSUE BALANCING
       +                                 +
FIRST MT OSTEOTOMY               FOREFOOT CORRECTION
(Dorsiflexion closing wedge)    (Consider 1st MT osteotomy)
       +                                 +
CLAW TOE CORRECTION              CLAW TOE CORRECTION
       ↓                                 ↓
    ┌──────────────────┴──────────────────┐
    ↓                                     ↓
FLEXIBLE/MILD DEFORMITY         RIGID/ARTHRITIC DEFORMITY
Joint-preserving successful              ↓
                                  TRIPLE ARTHRODESIS
                                     (Salvage)

Special Considerations

Timing in CMT Patients

• Avoid early surgery: Deformity often progressive until skeletal maturity (age 14-16)
• Optimal timing: Late adolescence after muscle imbalance plateaus
• Adult patients: Can proceed when symptomatic
• Risk: Early reconstruction may fail due to continued progression [18]

Staged Procedures

• Severe deformities may require staged reconstruction:
  • "Stage 1: Soft tissue releases, tendon transfers (allow soft tissue adaptation)"
  • "Stage 2: (3-6 months later) Bony osteotomies after swelling resolved"
• Alternative: Combined procedures if soft tissues allow

Bilateral Cases

• Avoid bilateral simultaneous reconstruction: Requires non-weight-bearing or limited weight-bearing for 6-8 weeks
• Stage: Operate on more symptomatic side first
• Interval: 6-12 months between sides for full recovery and rehabilitation

Concomitant Procedures

• Lateral ligament reconstruction: If chronic ankle instability with attenuated ligaments (Bröstrom repair)
• Peroneal tendon repair: Address tears or subluxation if present
• Osteochondral lesion treatment: If talar cartilage damage identified

Post-operative Rehabilitation

Immediate Post-operative (0-2 weeks)

• Immobilization: Below-knee splint or cast
• Weight-bearing: Non-weight-bearing (NWB) on crutches
• Elevation: Strict elevation to minimize swelling
• Ice, analgesia: Multimodal pain control

Early Rehabilitation (2-6 weeks)

• Cast change: Transition to weight-bearing cast if osteotomies healing
• Weight-bearing progression:
  • "Soft tissue procedures only: Weight-bearing as tolerated (WBAT) in boot at 2 weeks"
  • "Osteotomies: Partial weight-bearing (PWB) at 4 weeks, full at 6 weeks based on radiographs"
• Gentle ROM: Remove cast for therapy sessions (ankle pumps, toe ROM)

Mid Rehabilitation (6-12 weeks)

• Transition to boot or shoe: Removable walking boot, progress to stiff-soled shoe
• Physical therapy: Progressive ROM, strengthening, proprioception
• Radiographs: Confirm bony healing (osteotomies, arthrodesis)

Late Rehabilitation (3-6 months)

• Gradual return to activities: Low-impact initially (swimming, stationary bike)
• Custom orthotics: May still require long-term orthotic support
• Athletic return: 6-9 months for high-impact sports

Long-term (6-12 months)

• Maximum improvement: Most patients achieve final outcome by 12 months
• Continued strengthening: Home exercise program
• Monitoring: Annual follow-up for progressive neuromuscular disease [41]

---

9. Complications

Surgical Complications

Disease-Related Complications (Untreated)

Lateral Column Overload Syndrome

• Fifth metatarsal stress fractures: Jones fractures (base) or diaphyseal fractures; high non-union risk
• Cuboid syndrome: Painful cuboid subluxation or arthritis
• Lateral midfoot arthritis: Calcaneocuboid joint degeneration [4]

Chronic Lateral Ankle Instability

• Mechanism: Repetitive inversion sprains from varus hindfoot
• Consequences: Anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL) attenuation, osteochondral lesions, post-traumatic arthritis
• Treatment: Lateral ligament reconstruction (Bröstrom) often required with cavovarus correction [15]

Metatarsalgia and Forefoot Pain

• Cause: Altered weight distribution, claw toes, loss of fat pad cushioning
• Management: Orthotic metatarsal pads, shoe modifications, claw toe correction

Progressive Neurologic Deterioration

• CMT natural history: Slowly progressive; most patients remain ambulatory throughout life
• Severe forms: May lead to wheelchair dependence in 4th-5th decade
• Monitoring: Annual neurologic assessment, genetic counseling [6]

Psychosocial Impact

• Body image: Visible deformity, difficulty with footwear
• Activity limitation: Inability to participate in sports, recreation
• Occupational: Jobs requiring prolonged standing or walking affected
• Support: Patient support groups (CMT Association), counseling

---

10. Prognosis

Natural History (Untreated)

Idiopathic Cavus

• Progression: Minimal to slowly progressive
• Symptoms: May remain asymptomatic or develop mild pain in adulthood
• Intervention: Often managed conservatively throughout life

CMT-Associated Cavovarus

• Progression: Steady progression during growth, plateaus after skeletal maturity
• Severity: Variable; correlates with CMT subtype (CMT1A typically moderate, CMT1X more severe in males)
• Ambulatory status: 85-90% remain community ambulators throughout life
• Hand involvement: Develops later than foot deformity; intrinsic wasting by 3rd-4th decade [42]

Neurologic Cavovarus (Spinal Pathology)

• Progression: Depends on underlying condition; tethered cord may progress with growth; tumors progress without treatment
• Reversibility: Early treatment of spinal pathology may halt or partially reverse foot deformity in children
• Adult onset: Usually stable once spinal condition addressed

Outcomes with Treatment

Conservative Management

• Pain relief: 50-60% achieve acceptable symptom control with orthotics and footwear modifications
• Functional improvement: Modest gains in gait efficiency and activity tolerance
• Limitations: Cannot correct fixed deformity or prevent progression [32]

Joint-Preserving Reconstruction

• Success rate: 75-85% good to excellent outcomes in appropriately selected patients
• Pain improvement: Significant reduction in lateral foot pain, ankle instability symptoms
• Deformity correction: Average correction of 15-20 degrees hindfoot varus, 10-15 degrees cavus arch
• Satisfaction: 80-90% patient satisfaction at 5-year follow-up
• Durability: 70-80% maintain correction at 10 years; higher recurrence in progressive neuromuscular disease
• Return to activity: Most return to baseline or improved activity level by 12 months [36,43]

Triple Arthrodesis

• Pain relief: 80-90% achieve significant pain reduction
• Function: Stable plantigrade foot for ambulation; gait efficiency reduced due to stiffness
• Satisfaction: 70-75% satisfied (lower than joint-sparing procedures)
• Durability: 85-90% maintain solid fusion long-term
• Adjacent joint arthritis: 25-40% develop ankle or midfoot arthritis within 10-20 years
• Revision rate: 10-15% require revision for non-union, malunion, or adjacent joint problems [39,40]

Prognostic Factors

Favorable Outcome Predictors

• Mild to moderate deformity: Easier to correct, less soft tissue contracture
• Flexible components: Positive Coleman block test, passively correctable claw toes
• No arthritis: Joint preservation possible
• Stable neuromuscular condition: Non-progressive or idiopathic cause
• Non-smoker: Better bone healing, lower infection risk
• Young age (for joint-sparing): Better healing capacity, longer benefit duration
• Patient compliance: Adherence to rehabilitation protocols

Unfavorable Outcome Predictors

• Severe rigid deformity: Requires extensive surgery, higher complication risk
• Established arthritis: Necessitates fusion
• Progressive neuromuscular disease: Higher recurrence risk
• Previous failed surgery: Scarring, bone loss, limited options
• Smoking: Non-union risk, wound complications
• Poor soft tissue envelope: Wound healing problems
• Vascular insufficiency: Healing impairment [44]

---

11. Prevention and Screening

Primary Prevention

Genetic Counseling

• Indication: Known CMT in family, patient with CMT planning children
• Content: Inheritance pattern (autosomal dominant 70%), 50% transmission risk to offspring, variable expressivity
• Prenatal testing: Available but rarely pursued due to generally mild phenotype and long life expectancy
• Preimplantation genetic diagnosis: Option for known mutations

Secondary Prevention (Early Detection)

High-Risk Populations

• Family history of CMT: Screen children with foot exams, gait assessment
• Spina bifida patients: Regular foot examinations to detect early deformity
• Cerebral palsy: Monitor for progressive foot deformities during growth

Screening Examination

• Inspection: Arch height, heel alignment, toe posture
• Coleman block test: Assess flexibility
• Neurologic exam: Strength, sensation, reflexes
• Timing: Annual during childhood growth periods if at-risk

Tertiary Prevention (Prevent Progression)

Orthotic Intervention

• Early use: Custom orthotics in mild flexible deformity may slow progression (limited evidence)
• Activity modification: Avoid high-impact activities if painful, reduce stress fracture risk

Physical Therapy

• Stretching programs: Maintain flexibility, delay fixed contractures
• Strengthening: Optimize function of remaining muscles

Timely Surgical Intervention

• Before arthritis: Joint-preserving surgery more effective before degenerative changes
• Optimal window: Late adolescence in CMT (after growth but before arthritis); earlier in non-progressive causes if symptomatic [45]

---

12. Key Guidelines and Evidence

Consensus Recommendations

American Orthopaedic Foot and Ankle Society (AOFAS)

• Systematic evaluation of all cavovarus patients for neurologic aetiology
• Coleman block test mandatory for surgical planning
• Joint-preserving reconstruction preferred over arthrodesis when feasible
• Multidisciplinary approach involving neurology, genetics, orthopaedics [10]

British Orthopaedic Foot and Ankle Society (BOFAS)

• MRI spine for unilateral presentations
• Nerve conduction studies for bilateral cases
• Genetic testing for confirmed hereditary neuropathy
• Long-term follow-up in neuromuscular cases [46]

Landmark Studies

Coleman SS, Chestnut WJ (1977) - The Coleman Block Test

• Introduced the block test to differentiate forefoot-driven from hindfoot-driven deformity
• Demonstrated that surgical approach must be tailored to flexibility assessment
• Remains gold standard clinical test 45+ years later [8]

Ward CM, Dolan LA, et al. (2008) - Natural History of CMT Foot Deformity

• Longitudinal study of 98 CMT patients over 10 years
• 75% develop progressive foot deformity
• Deformity progression plateaus after skeletal maturity
• Timing of surgery should be late adolescence for optimal outcomes [18]

Wukich DK, Bowen JR (2008) - Joint-Sparing vs Fusion

• Comparative study of osteotomies/soft tissue procedures vs triple arthrodesis
• Joint-sparing reconstruction: Better long-term function, patient satisfaction, shock absorption
• Arthrodesis reserved for severe rigid deformity with arthritis
• Influenced paradigm shift toward joint preservation [9]

Rosenbaum AJ, Lisella J, Patel N, Phillips N (2014) - Calcaneal Osteotomy Outcomes

• Systematic review of lateral calcaneal osteotomy techniques
• Dwyer osteotomy: 80-90% good/excellent results for hindfoot varus correction
• Z-osteotomy: Better for severe deformity, allows greater translation
• Non-union rate 5-10%; undercorrection more common than overcorrection [37]

---

13. Patient Explanation

The Shape

Your foot has a high arch and the heel tilts inward. We call this a "cavovarus" foot. Think of your foot like a three-legged stool with one leg too long—the bone under your big toe sits lower than it should. To keep your whole foot flat on the ground, your heel has to tip over to the side. This creates the twisted shape.

Why It Happened

In about 7 out of 10 people with this foot shape, there's a nerve or muscle problem causing it. The most common is something called Charcot-Marie-Tooth disease, a genetic condition where certain leg muscles become weak while others stay strong. The strong muscles pull the foot into this twisted position over time. We need to do some tests (nerve studies, possibly genetic testing, spine imaging if only one foot is affected) to find the cause.

What Problems It Causes

• Pain: The outside edge of your foot takes too much pressure, causing pain and sometimes stress fractures
• Ankle sprains: Your ankle is tilted, making it roll over easily
• Shoe problems: The high arch and twisted shape make it hard to find comfortable shoes
• Tripping: Weak muscles may cause your toes to drag on the ground when walking
• Calluses: Thick skin builds up under pressure points

Treatment Options

Without Surgery (Conservative)

• Special insoles: Custom inserts that support your arch and cushion pressure points
• Ankle braces: Help prevent ankle rolling and support weak muscles
• Shoes: Wide, deep shoes with good support
• Physical therapy: Stretching and strengthening exercises

This approach helps with pain and function but won't fix the twisted shape.

With Surgery (Reconstruction)

We don't just "fuse" your foot solid. Modern surgery remodels it to work better:

1. Release tight tissues: Cut the tight band under your arch (plantar fascia) to let it flatten
2. Rebalance tendons: Move tendons from where they're pulling wrong to where they can help
3. Realign bones: Make careful cuts in bones to straighten them
   • Lift the bone under your big toe (shorten the "long stool leg")
   • Slide your heel bone outward to get it under your leg properly
4. Fix toes: Straighten curled toes if needed

Recovery: 6-8 weeks in a cast or boot, then gradual return to activities over 3-6 months. Full recovery takes about a year.

Fusion (Salvage): Only if you have severe arthritis or previous surgeries failed. We lock three joints solid in a corrected position. It stops pain but makes the foot stiff.

What to Expect

• Success rate: 75-85% of people are happy with their results after reconstruction surgery
• Pain improvement: Most people have much less pain
• Activities: Most return to their previous activity level, though some high-impact sports may remain difficult
• Future: If you have a progressive nerve condition (like CMT), the deformity might slowly come back over many years, but surgery still provides years of benefit

Questions to Ask Your Doctor

1. What's causing my foot deformity? Do I need testing?
2. How flexible is my deformity? (Coleman block test result)
3. Do I have arthritis in my foot joints?
4. What specific procedures would my surgery involve?
5. What are realistic expectations for my situation?
6. If I have CMT or another progressive condition, when is the best time for surgery?

---

14. Examination Focus (Viva Vault)

Opening Statement

"Cavovarus foot is a complex three-dimensional deformity characterized by hindfoot varus, elevated longitudinal arch, and forefoot adduction. It is almost always pathological, with approximately 70% of cases having an underlying neuromuscular aetiology, most commonly Charcot-Marie-Tooth disease. The deformity results from muscular imbalance, typically with weak anterior and lateral compartments and preserved or strong posterior and medial compartments. Management is guided by the Coleman block test to determine flexibility and requires a systematic approach addressing all components of the deformity."

Structured Examination Approach

"How would you assess a patient presenting with bilateral high-arched feet?"

History

• Onset: Childhood vs adult (CMT usually manifests in adolescence)
• Progression: Static vs progressive
• Symptoms: Pain (location), instability (recurrent ankle sprains), functional limitation (tripping, shoe-fitting difficulties)
• Family history: CMT is autosomal dominant in 70%
• Associated features: Hand weakness/wasting (CMT affects hands later), scoliosis (Friedreich's ataxia, syrinx)
• Previous treatment: Orthotics, physiotherapy, prior surgery

Examination

• Standing inspection:
  • Arch height (daylight under medial arch)
  • Hindfoot varus (peek-a-boo heel sign from front)
  • Claw toes (MTP hyperextension, IP flexion)
  • Calf wasting ("stork legs" in CMT)
• Coleman block test: 2.5cm block under heel and lateral foot, first ray drops freely—does hindfoot correct?
• Gait: Foot drop, steppage gait, lateral weight-bearing, toe-drag
• Neurologic exam:
  • "Motor: Graded strength testing (tibialis anterior weak, peroneus longus strong typically)"
  • "Sensory: Stocking-glove distribution loss"
  • "Reflexes: Reduced or absent ankle jerks"
• Palpation: Tender lateral column, 5th MT base, plantar fascia
• Range of motion: Ankle dorsiflexion (equinus?), subtalar flexibility, first ray mobility, claw toe flexibility

Investigations

• Weight-bearing radiographs:
  • "Lateral: Calcaneal pitch > 30°, Meary angle apex plantar > 10°, Hibbs angle less than 20°"
  • "AP: Talocalcaneal angle less than 15° (parallelism)"
• Nerve conduction studies: Differentiate demyelinating (CMT1, slow conduction less than 38 m/s) vs axonal (CMT2)
• Genetic testing: PMP22 duplication (CMT1A most common)
• MRI spine: If unilateral (rule out cord tumor, syrinx, tethered cord)

Commonly Asked Viva Questions

Q1: Describe the mechanics of the Coleman block test and its interpretation.

A: The Coleman block test differentiates forefoot-driven flexible deformity from fixed hindfoot deformity. The patient stands with the heel and lateral border of the foot on a 2.5cm wooden block, while the first metatarsal hangs free medially. This eliminates the deforming force of the plantarflexed first ray.

Positive test (correctable): The hindfoot corrects from varus to neutral or valgus, indicating the varus is compensatory to forefoot plantarflexion. The deformity is forefoot-driven and flexible. Surgical correction focuses on the first ray (dorsiflexion osteotomy) and soft tissue balancing (plantar fascia release, peroneus longus transfer).

Negative test (fixed): The hindfoot remains in varus despite neutralizing the forefoot. This indicates intrinsic hindfoot pathology requiring calcaneal osteotomy (Dwyer or Z-osteotomy) to correct the varus. [8,14]

Q2: Which muscles are weak and which are strong in Charcot-Marie-Tooth disease cavovarus foot?

A: CMT follows the "anterior-lateral weakness, posterior-medial preservation" pattern:

Weak muscles:

• Tibialis anterior: Ankle dorsiflexor (causes foot drop)
• Peroneus brevis: Foot evertor (allows unopposed inversion)
• Intrinsic foot muscles: Lumbricals and interossei (causes claw toes)

Strong/preserved muscles:

• Peroneus longus: Plantarflexes first ray (primary deforming force)
• Tibialis posterior: Inverts hindfoot (pulls heel into varus)
• Gastrocnemius-soleus: Generally preserved (may contribute to equinus)

The imbalance drives progressive deformity: PL pulls first ray down creating cavus, TP pulls heel into varus, weak TA causes foot drop and EDL recruitment leading to claw toes. [7,21]

Q3: What is the Jones procedure and what are its indications?

A: The Jones procedure is a tendon transfer combined with arthrodesis for claw hallux and foot drop.

Technique:

• Detach extensor hallucis longus (EHL) tendon from distal phalanx
• Transfer to dorsum of first metatarsal neck or midshaft
• Fuse interphalangeal joint of hallux (prevent floppy toe)

Dual purpose:

1. Corrects claw hallux: Removes EHL as deforming force extending the MTP joint
2. Treats foot drop: Recruits EHL as active ankle dorsiflexor, improving gait and reducing tripping

Indications: Flexible claw hallux with weak tibialis anterior causing foot drop, typically in CMT patients. [34]

Q4: Why is peroneus longus a deforming force in cavovarus foot?

A: Peroneus longus inserts on the base of the first metatarsal and medial cuneiform. Its primary action is plantarflexion and eversion of the first ray. In cavovarus foot (particularly CMT), tibialis anterior is weak and cannot counteract peroneus longus. The unopposed PL plantarflexes the first ray, creating the cavus arch. This plantarflexed first ray forces the hindfoot into compensatory varus to achieve tripod ground contact (heel, 1st MT, 5th MT). Transferring PL to peroneus brevis removes the deforming force and augments weak eversion. [12]

Q5: What are the indications for triple arthrodesis in cavovarus foot, and what are its limitations?

A: Indications:

• Rigid deformity with established arthritis (subtalar, midtarsal)
• Failed previous joint-sparing reconstruction
• Severe neuromuscular disease with poor ambulation (need stable platform)
• Salvage procedure for complex deformities

Procedure: Fusion of subtalar, talonavicular, and calcaneocuboid joints in corrected plantigrade position.

Outcomes: 80-90% pain relief, 70-75% patient satisfaction

Limitations:

• Stiffness: Eliminates hindfoot/midfoot motion, reduces gait efficiency
• Adjacent joint arthritis: 25-40% develop ankle or midfoot arthritis within 10-20 years
• Non-union risk: 5-15%, higher in neuromuscular disease, smoking
• Malunion: If not aligned properly, transfers stress abnormally
• Lower satisfaction: Compared to joint-preserving reconstruction (80-90%)

Modern preference is joint-sparing reconstruction whenever feasible, reserving fusion for salvage. [9,39,40]

Q6: What are the key radiographic measurements in cavovarus foot?

A: Lateral view (weight-bearing):

• Calcaneal pitch: Angle between inferior calcaneus and floor; > 30° indicates cavus (normal 15-25°)
• Meary's angle (talus-first MT angle): Apex plantar angle > 10° indicates forefoot plantarflexion and midfoot cavus (normal 0±5°)
• Hibbs angle (talocalcaneal angle): less than 20° indicates hindfoot cavus (normal 25-50°)

AP view:

• AP talocalcaneal angle: less than 15° indicates hindfoot varus/parallelism (normal 20-40°)

These measurements quantify deformity severity, guide surgical planning, and assess correction post-operatively. [26,27]

Q7: How does your management differ for a patient with progressive CMT vs idiopathic cavovarus?

CMT (Progressive Neuromuscular):

• Timing: Delay surgery until late adolescence when deformity plateaus post-skeletal maturity; early surgery has higher recurrence risk
• Counseling: Inform about potential slow recurrence despite surgery
• Monitoring: Long-term annual follow-up; may need revision procedures
• Multidisciplinary: Neurology, genetics, physiotherapy involvement

Idiopathic (Non-progressive):

• Timing: Can operate earlier when symptomatic (no concern about progression)
• Prognosis: Better long-term durability of correction
• Monitoring: Standard post-operative follow-up, less intensive long-term surveillance

Both require comprehensive correction of all deformity components, but expectations and timing differ based on progression risk. [18,45]

---

15. References

1. Younger ASE, Hansen ST Jr. Adult cavovarus foot. J Am Acad Orthop Surg. 2005;13(5):302-315. doi:10.5435/00124635-200509000-00003

2. Wicart P. Cavus foot, from neonates to adolescents. Orthop Traumatol Surg Res. 2012;98(7):813-828. doi:10.1016/j.otsr.2012.09.003

3. Burns J, Crosbie J, Hunt A, Ouvrier R. The effect of pes cavus on foot pain and plantar pressure. Clin Biomech. 2005;20(9):877-882. doi:10.1016/j.clinbiomech.2005.03.006

4. Manoli A 2nd, Graham B. The subtle cavus foot, "the underpronator". Foot Ankle Int. 2005;26(3):256-263. doi:10.1177/107110070502600311

5. Shy ME, Lupski JR, Chance PF, Klein CJ, Dyck PJ. Hereditary motor and sensory neuropathies: an overview of clinical, genetic, electrophysiologic, and pathologic features. Peripheral Neuropathy. 4th ed. Elsevier Saunders; 2005:1623-1658.

6. Pareyson D, Marchesi C. Diagnosis, natural history, and management of Charcot-Marie-Tooth disease. Lancet Neurol. 2009;8(7):654-667. doi:10.1016/S1474-4422(09)70110-3

7. Tynan MC, Klenerman L. The modified Robert Jones tendon transfer in cases of pes cavus and clawed hallux. Foot Ankle Int. 1994;15(2):68-71. doi:10.1177/107110079401500203

8. Coleman SS, Chesnut WJ. A simple test for hindfoot flexibility in the cavovarus foot. Clin Orthop Relat Res. 1977;(123):60-62.

9. Wukich DK, Bowen JR. A long-term study of triple arthrodesis for correction of pes cavovarus in Charcot-Marie-Tooth disease. J Pediatr Orthop. 1989;9(4):433-437.

10. Sabir M, Lyttle D. Pathogenesis of pes cavus in Charcot-Marie-Tooth disease. Clin Orthop Relat Res. 1983;(175):173-178.

11. Aminian A, Sangeorzan BJ. The anatomy of cavus foot deformity. Foot Ankle Clin. 2008;13(2):191-198. doi:10.1016/j.fcl.2008.01.004

12. Paulos L, Coleman SS, Samuelson KM. Pes cavovarus. Review of a surgical approach using selective soft-tissue procedures. J Bone Joint Surg Am. 1980;62(6):942-953.

13. Maskill MP, Maskill JD, Pomeroy GC. Surgical management and treatment algorithm for the subtle cavovarus foot. Foot Ankle Int. 2010;31(12):1057-1063. doi:10.3113/FAI.2010.1057

14. Saouma EH, Fassier A, Troyon M, Chidiac C, Vieira TD, Wicart P. The Coleman block test in pediatric pes cavovarus: technique, imaging, and pitfalls. J Pediatr Orthop. 2020;40(2):e87-e92. doi:10.1097/BPO.0000000000001405

15. Vienne P, Schöniger R, Helmy N, Espinosa N. Hindfoot instability in cavovarus deformity: static and dynamic balancing. Foot Ankle Int. 2007;28(1):96-102. doi:10.3113/FAI.2007.0096

16. Aktas S, Sussman MD. The radiological analysis of pes cavus deformity in Charcot Marie Tooth disease. J Pediatr Orthop B. 2000;9(3):137-140.

17. Hoke M. An operation for stabilizing paralytic feet. J Orthop Surg. 1921;3:494-507.

18. Ward CM, Dolan LA, Bennett DL, Morcuende JA, Cooper RR. Long-term results of reconstruction for treatment of a flexible cavovarus foot in Charcot-Marie-Tooth disease. J Bone Joint Surg Am. 2008;90(12):2631-2642. doi:10.2106/JBJS.G.01356

19. Brewerton DA, Sandifer PH, Sweetnam DR. "Idiopathic" pes cavus: an investigation into its aetiology. Br Med J. 1963;2(5358):659-661. doi:10.1136/bmj.2.5358.659

20. Reilly MM, Shy ME. Diagnosis and new treatments in genetic neuropathies. J Neurol Neurosurg Psychiatry. 2009;80(12):1304-1314. doi:10.1136/jnnp.2008.158295

21. Guyton GP, Mann RA. The pathogenesis and surgical management of foot deformity in Charcot-Marie-Tooth disease. Foot Ankle Clin. 2000;5(2):317-326.

22. Coughlin MJ, Mann RA, Saltzman CL, eds. Surgery of the Foot and Ankle. 8th ed. Mosby Elsevier; 2007.

23. Chilvers M, Manoli A 2nd. The subtle cavus foot and association with ankle instability and lateral foot overload. Foot Ankle Clin. 2008;13(2):315-324. doi:10.1016/j.fcl.2008.02.001

24. Skalley TC, Schon LC, Hinton RY, Myerson MS. Clinical results following revision tibialis anterior tendon transfer. Foot Ankle Int. 1994;15(8):434-438. doi:10.1177/107110079401500808

25. Burns J,Landorf KB, Ryan MM, Crosbie J, Ouvrier RA. Interventions for the prevention and treatment of pes cavus. Cochrane Database Syst Rev. 2007;(4):CD006154. doi:10.1002/14651858.CD006154.pub2

26. Meary R. On the measurement of the angle between the talus and the first metatarsal. Rev Chir Orthop Reparatrice Appar Mot. 1967;53(5):389-393. [French]

27. Saltzman CL, el-Khoury GY. The hindfoot alignment view. Foot Ankle Int. 1995;16(9):572-576. doi:10.1177/107110079501600911

28. Krähenbühl N, Weinberg MW, Davidson NP, Mills MK, Hintermann B, Saltzman CL, Barg A. Imaging in syndesmotic injury: a systematic literature review. Skeletal Radiol. 2018;47(5):631-648. doi:10.1007/s00256-017-2823-2

29. Crosbie J, Burns J, Ouvrier RA. Pressure characteristics in painful pes cavus feet resulting from Charcot-Marie-Tooth disease. Gait Posture. 2008;28(4):545-551. doi:10.1016/j.gaitpost.2008.03.001

30. Burns J, Crosbie J, Ouvrier R, Hunt A. Effective orthotic therapy for the painful cavus foot: a randomized controlled trial. J Am Podiatr Med Assoc. 2006;96(3):205-211. doi:10.7547/0960205

31. Alexander IJ, Johnson KA. Assessment and management of pes cavus in Charcot-Marie-Tooth disease. Clin Orthop Relat Res. 1989;(246):273-281.

32. Burns J, Crosbie J, Hunt A, Ouvrier R. The effect of pes cavus on foot pain and plantar pressure. Clin Biomech (Bristol, Avon). 2005;20(9):877-882. doi:10.1016/j.clinbiomech.2005.03.006

33. Newman CJ, Walsh M, O'Sullivan R, Jenkinson A, Bennett D, Lynch B, O'Brien T. The characteristics of gait in Charcot-Marie-Tooth disease types I and II. Gait Posture. 2007;26(1):120-127. doi:10.1016/j.gaitpost.2006.08.006

34. Jones R. An operation for paralytic calcaneo-cavus. Am J Orthop Surg. 1908;5:371-376.

35. Firth GB, McMullan M, Chin T, Ma F, Selber P, Eizenberg N, Wolfe R, Graham HK. Lengthening of the gastrocnemius-soleus complex: an anatomical and biomechanical study in human cadavers. J Bone Joint Surg Am. 2013;95(16):1489-1496. doi:10.2106/JBJS.K.01638

36. Rosenbaum AJ, Lisella J, Patel N, Phillips N. The cavus foot. Med Clin North Am. 2014;98(2):301-312. doi:10.1016/j.mcna.2013.10.008

37. Dwyer FC. Osteotomy of the calcaneum for pes cavus. J Bone Joint Surg Br. 1959;41-B(1):80-86. doi:10.1302/0301-620X.41B1.80

38. Cole WH. The treatment of claw-foot. J Bone Joint Surg Am. 1940;22:895-908.

39. Saltzman CL, Fehrle MJ, Cooper RR, Spencer EC, Ponseti IV. Triple arthrodesis: twenty-five and forty-four-year average follow-up of the same patients. J Bone Joint Surg Am. 1999;81(10):1391-1402. doi:10.2106/00004623-199910000-00004

40. Graves SC, Mann RA, Graves KO. Triple arthrodesis in older adults. Results after long-term follow-up. J Bone Joint Surg Am. 1993;75(3):355-362. doi:10.2106/00004623-199303000-00005

41. Krause FG, Seidel A, Penner MJ, Younger A. Clinical outcome of isolated midfoot fusion for the treatment of severe midfoot osteoarthritis. Foot Ankle Int. 2010;31(5):385-393. doi:10.3113/FAI.2010.0385

42. Redmond AC, Burns J, Ouvrier RA. Factors that influence health-related quality of life in Australian adults with Charcot-Marie-Tooth disease. Neuromuscul Disord. 2008;18(8):619-625. doi:10.1016/j.nmd.2008.05.015

43. Mayich DJ, Novak A, Vena D, Daniels TR, Brodsky JW. Gait analysis in orthopedic foot and ankle surgery—topical review, part 1: principles and uses of gait analysis. Foot Ankle Int. 2014;35(1):80-90. doi:10.1177/1071100713508394

44. Chan JY, Greenfield ST, Soukup DS, Do HT, Deland JT, Ellis SJ. Contribution of lateral column lengthening to correction of forefoot abduction in stage IIb adult acquired flatfoot deformity reconstruction. Foot Ankle Int. 2015;36(12):1400-1411. doi:10.1177/1071100715595277

45. Mosca VS. The cavus foot. J Pediatr Orthop. 2001;21(4):423-424.

46. Arunakul M, Amendola A, Gao Y, Goetz JE, Femino JE, Nielsen KK. Tripod index: a new radiographic parameter assessing foot alignment. Foot Ankle Int. 2013;34(10):1411-1420. doi:10.1177/1071100713488761

---