# Foot Cavovarus - Charcot-Marie-Tooth ## Clinical Scenario A 25-year-old male presents with progressive bilateral foot deformity and recurrent lateral ankle sprains. He has difficulty with shoe wear and calluses under the first and fifth metatarsal heads. On examination, he has high-arched feet with hindfoot varus that corrects with Coleman block test. He has subtle weakness of ankle dorsiflexion and EHL. ## Questions & Model Answers The likely diagnosis is Charcot-Marie-Tooth disease (CMT/hereditary motor sensory neuropathy type 1A), the most common cause of cavovarus foot in adults. The combination of progressive bilateral cavovarus deformity with peroneal weakness and ankle instability is classic. Investigations: 1) Nerve conduction studies/EMG - will show demyelinating neuropathy with reduced conduction velocities, 2) Genetic testing - CMT1A is most common (PMP22 duplication), 3) MRI spine - exclude other causes like tethered cord, diastematomyelia, spinal tumour, 4) Standing foot and ankle X-rays - assess bone deformity, Meary's angle, calcaneal pitch, 5) Referral to neurologist for complete assessment. Differential diagnosis: polio, cerebral palsy, Friedreich's ataxia, spinal dysraphism, idiopathic cavus. **Key Points:** - CMT most common cause of adult cavovarus - NCS/EMG and genetic testing diagnostic - MRI spine to exclude other causes - Bilateral symmetric involvement typical Coleman block test: Patient stands on a wooden block with the lateral border of the foot on the block and first metatarsal head hanging off the edge. This eliminates the plantarflexed first ray's contribution to hindfoot varus. Interpretation: 1) If hindfoot corrects to neutral/valgus = flexible hindfoot, forefoot-driven cavus (most common), treat the forefoot first, 2) If hindfoot remains in varus = rigid hindfoot, will need hindfoot osteotomy. Treatment implications for flexible (forefoot-driven) cavus: 1) Correct plantarflexed first ray first - dorsiflexion osteotomy of first metatarsal or midfoot, 2) Then reassess hindfoot - often corrects spontaneously, 3) May still need soft tissue rebalancing - peroneus longus to brevis transfer (removes first ray plantarflexion force and reinforces weak peroneus brevis). **Key Points:** - Coleman block differentiates forefoot vs hindfoot driven - Flexible hindfoot = treat forefoot first - Fixed hindfoot = need calcaneal osteotomy - Addresses deformity systematically from front to back Surgical approach for flexible cavovarus (assuming Coleman block positive): 1) First metatarsal dorsiflexion osteotomy - elevates plantarflexed first ray, 2) Peroneus longus to brevis transfer - removes deforming force on first ray, augments weak ankle eversion, 3) Plantar fascia release - if contributing to high arch, 4) Toe procedures - extensor tendon transfers (EHL to neck of first MT, EDL to lesser MTs) for claw toes, flexor-to-extensor transfer (Girdlestone) if severe, 5) Reassess hindfoot - if still varus, add lateral closing wedge calcaneal osteotomy (Dwyer), 6) Lateral ankle ligament reconstruction - for chronic instability (Brostrom-Gould), must address bony deformity first or ligament reconstruction will fail. For rigid cavovarus: may need triple arthrodesis if very severe, but loses hindfoot motion so reserved for end-stage. **Key Points:** - Systematic approach from front to back - Correct forefoot first, then reassess hindfoot - Peroneus longus transfer important - Lateral ankle reconstruction last, after bony correction Postoperative management: Immediate: 1) Non-weight-bearing cast/boot for 6-8 weeks (allows osteotomies to heal), 2) Leg elevation and swelling management, 3) VTE prophylaxis, 4) Pain management. Transition to weight-bearing: 1) Progressive weight-bearing in walking boot from 6-8 weeks, 2) Transition to supportive footwear by 10-12 weeks. Rehabilitation: 1) Physiotherapy for ROM and strengthening once healed, 2) Proprioception training (especially after lateral ankle reconstruction), 3) Gait retraining, 4) Ongoing muscle strengthening - particularly peroneals and ankle dorsiflexors. Long-term management: 1) Custom orthotics - lateral wedge, arch support, 2) Ankle-foot orthoses (AFO) if significant drop foot, 3) Appropriate footwear - high-top boots, rocker soles, 4) Surveillance for disease progression (CMT is progressive). Time to maximal improvement: 6-12 months for functional recovery. Return to activities: 4-6 months for daily activities, 6-12 months for higher-level activities. **Key Points:** - Non-weight-bearing 6-8 weeks for osteotomies - Orthotics and supportive footwear long-term - AFO if significant drop foot - CMT is progressive - may need future surgery Progressive disease management: CMT natural history: Progressive muscle weakness and wasting, typically slow, most functional decline in first 2 decades after onset. Indications for revision surgery: 1) Recurrent deformity - flexible initially may become rigid, 2) Progression of muscle weakness requiring additional tendon transfers, 3) Development of rigid hindfoot requiring arthrodesis, 4) Ankle arthritis from chronic instability. Revision options: 1) Additional tendon transfers - posterior tibial tendon transfer through interosseous membrane for drop foot, 2) Triple arthrodesis - for rigid hindfoot (fuses subtalar, talonavicular, calcaneocuboid), sacrifices hindfoot motion but provides stable plantigrade foot, 3) Ankle fusion or replacement - for end-stage ankle arthritis, 4) Pantalar arthrodesis - severe combined hindfoot and ankle disease. Prevention of progression: Regular physiotherapy, orthotic management, early intervention when deformity progresses. Life expectancy: Normal in most CMT patients, functional decline more significant than survival impact. **Key Points:** - CMT is progressive - plan for long-term surveillance - Triple arthrodesis for rigid hindfoot - Additional tendon transfers for progressive weakness - Orthotic management slows need for revision Prognosis and outcomes: Surgical outcomes: 1) Pain relief - 85-90% significant improvement, 2) Correction of deformity - 80-85% maintain plantigrade foot at 5 years, 3) Reduced ankle sprains - significant reduction in instability episodes, 4) Improved footwear tolerance - ability to wear normal shoes, 5) Improved gait efficiency. Factors affecting outcome: 1) Underlying aetiology - non-progressive causes (idiopathic, post-trauma) better than CMT, 2) Severity of deformity at presentation, 3) Flexibility (Coleman block positive = better outcome), 4) Age at surgery, 5) Muscle strength preservation. Complications: 1) Non-union of osteotomies (5%), 2) Recurrence of deformity (10-20% at 10 years in CMT), 3) Overcorrection (valgus), 4) Stiffness, 5) Nerve injury (sural, superficial peroneal), 6) Wound complications. Long-term expectations: For this patient with CMT: Good functional improvement expected, but disease progression may require further intervention over lifetime. Counsel regarding realistic expectations. **Key Points:** - 85-90% pain relief, 80-85% maintained correction - CMT patients may need revision surgery - Recurrence 10-20% at 10 years - Flexibility (Coleman positive) predicts better outcome ## Exam Tips **Opening Statement:** This patient has bilateral cavovarus feet likely due to Charcot-Marie-Tooth disease. The positive Coleman block test indicates flexible hindfoot with forefoot-driven deformity. Surgical correction would address the plantarflexed first ray first, followed by soft tissue rebalancing and lateral ankle stabilisation. **Common Pitfalls:** - Don't reconstruct ankle ligaments without correcting bony deformity - Always investigate underlying cause in adult-onset cavus - Progressive disease may need revision surgery over time