Cavovarus Foot

Cavovarus foot is characterised by an elevated medial longitudinal arch (cavus), hindfoot varus, and plantar flexion of the first ray. Unlike the planovalgus foot, the cavovarus foot is rigid and loads the lateral column and heel excessively. The deformity is most commonly neurological in origin, and identifying the underlying cause — particularly distinguishing hereditary motor and sensory neuropathy (HMSN/Charcot-Marie-Tooth) from other neurological causes — is the essential first step in management.

• The most important principle in cavovarus foot: always look for an underlying neurological cause — approximately 60–70% of cases are neurological; Charcot-Marie-Tooth (CMT) disease is the most common cause; unilateral or asymmetric cavovarus deformity has a higher likelihood of a spinal or intracranial cause (diastematomyelia, spinal cord tumour, tethered cord)
• Aetiology classification:

• CMT disease (HMSN): most common inherited peripheral neuropathy; autosomal dominant most commonly; characterised by progressive distal muscle weakness and wasting, sensory loss, and areflexia; produces the characteristic foot deformity due to differential weakness of intrinsic foot muscles and specific extrinsic muscle groups
• Muscle imbalance in CMT producing cavovarus: peroneus brevis (weak) vs peroneus longus (relatively stronger initially) — peroneus longus plantarflexes the first ray unopposed → forefoot-driven cavus; tibialis anterior (weak) vs tibialis posterior (stronger) → hindfoot varus; intrinsic muscle weakness → clawing of toes (intrinsic minus foot)
• CMT Type 1A: most common subtype; PMP22 gene duplication on chromosome 17; demyelinating; slow nerve conduction velocity; autosomal dominant
• CMT Type 2: axonal type; MFN2 gene mutation most common; less severe than Type 1A; less foot deformity in many cases
• Clinical features: "champagne bottle" lower legs (distal muscle wasting with preserved proximal bulk); pes cavus; hammer/claw toes; stocking sensory loss; absent ankle reflexes; positive family history
• Electromyography (EMG) and nerve conduction studies (NCS): essential investigation — slowed NCV in demyelinating CMT1; reduced CMAP amplitude in axonal CMT2; confirms peripheral neuropathy and characterises severity; genetic testing for PMP22 duplication

• Symptoms: lateral ankle instability (most common presenting complaint); lateral foot and heel pain from overloading; callosity under 1st and 5th metatarsal heads; difficulty with footwear; ankle sprains
• Coleman block test: key examination to determine the driving force of the deformity — the patient stands with a 1–2 cm wooden block under the lateral border of the foot only; if the hindfoot corrects to neutral, the deformity is forefoot-driven (first ray plantarflexion is the primary deformity); if the hindfoot remains in varus, it is hindfoot-driven (fixed varus); this test determines whether calcaneal osteotomy alone is sufficient or whether first ray procedures are also required
• Assess: arch height (weight-bearing and non-weight-bearing), hindfoot alignment (from behind), toe posture (claw/hammer), ankle stability, muscle power (specifically peroneus longus, peroneus brevis, tibialis anterior, tibialis posterior), sensory testing
• Foot flexibility: rigid vs flexible deformity on passive manipulation — determines whether osteotomy or arthrodesis is required
• Neurological examination: gait assessment, balance, proprioception, reflexes — full neurological examination to identify any central or spinal component

• Weight-bearing foot and ankle radiographs: AP and lateral; assess Meary angle (elevated in cavus), calcaneal pitch angle (elevated >30° in cavus), hindfoot alignment view
• Calcaneal pitch angle (lateral WB X-ray): angle between plantar surface of calcaneus and floor; normal 18–20°; >30° = elevated pitch = cavus deformity
• MRI spine: mandatory in unilateral or asymmetric cavovarus deformity — exclude tethered cord, syringomyelia, intraspinal tumour; also in rapidly progressive deformity
• EMG/NCS: for suspected neuropathy; characterises nerve involvement pattern
• Genetic testing: CMT gene panel (PMP22 duplication first); valuable for counselling, prognosis, and family screening
• Whole-spine X-rays: for associated scoliosis in Friedreich ataxia and CMT

• Lateral heel posting and custom orthotics: redistribute loading from lateral column to medial; unload the 5th metatarsal head; provide hindfoot support
• Ankle-foot orthosis (AFO): for associated foot drop or significant ankle instability; accommodates deformity in rigid cases
• Footwear modification: high-top shoes for ankle support; wide toe box for clawed toes; lateral wedging
• Physiotherapy: peroneal strengthening, ankle stability training, balance rehabilitation; slows progression but does not reverse established deformity
• Non-operative management is appropriate for mild-moderate deformity, flexible deformity in young patients, poor surgical candidates; progressive neurological disease may require reassessment as deformity worsens

Surgical correction of cavovarus foot is tailored to the specific components of the deformity and the flexibility assessment. The surgical plan addresses the deformity from proximal to distal (or distal to proximal, depending on the driving force identified by the Coleman block test).

• The surgical principle in flexible cavovarus: perform soft tissue and osteotomy procedures to balance the foot and correct the deformity while preserving joint motion; triple arthrodesis is reserved for rigid, arthritic, or severe deformity where joint preservation is not feasible — it is not a primary procedure in flexible cavovarus

• Progressive cavovarus: in CMT and other neuropathies, the underlying disease continues to progress after surgical correction; patients should be counselled that surgery addresses the current deformity but does not halt neurological progression; reoperation may be required as the disease progresses; long-term follow-up is essential
• Friedreich ataxia: autosomal recessive spinocerebellar ataxia (GAA repeat expansion in frataxin gene); cavovarus foot is present in approximately 90%; associated with scoliosis, hypertrophic cardiomyopathy, and diabetes; cardiomyopathy is the most common cause of death; foot surgery addresses the foot deformity but overall prognosis is poor; surgical decision must account for progressive disease
• Spinal cord pathology presenting as cavovarus: a unilateral progressive cavovarus deformity, particularly in a child with no family history, should prompt urgent MRI of the whole spine; tethered cord, syringomyelia, and spinal cord tumours are important and treatable causes; neurosurgical referral before orthopaedic intervention in these cases
• Overcorrection to planovalgus after triple arthrodesis: the most common error in triple arthrodesis for cavovarus is residual hindfoot varus or overcorrection into valgus; valgus overcorrection causes lateral ankle pain, fibular stress fractures, and peroneal tendon dysfunction; precise intraoperative positioning and post-operative X-ray assessment is essential

• Always look for neurological cause — CMT most common (60–70%); unilateral/asymmetric = MRI spine urgently (tethered cord, syrinx)
• CMT muscle imbalance: peroneus longus stronger than brevis → first ray plantarflexion; tibialis posterior stronger than anterior → hindfoot varus; intrinsic weakness → claw toes
• Coleman block test: lateral block under foot — hindfoot corrects = forefoot-driven; remains in varus = hindfoot-driven; guides surgical plan
• Forefoot-driven: first metatarsal dorsiflexion osteotomy primary; hindfoot-driven: calcaneal osteotomy primary
• Calcaneal pitch angle >30° = cavus on lateral WB X-ray; Meary line broken with plantar apex
• CMT Type 1A: PMP22 duplication chromosome 17; demyelinating; slow NCV; autosomal dominant
• Triple arthrodesis: last resort for rigid fixed deformity — not a primary procedure in flexible cavovarus
• Plantar fascia release (Steindler): releases plantar fascia contracture; risk of overcorrection to planovalgus if excessive
• Friedreich ataxia: cavovarus + scoliosis + hypertrophic cardiomyopathy; cardiomyopathy = most common cause of death
• Progressive disease in CMT: surgery corrects current deformity but does not halt progression — long-term follow-up and possible reoperation required