The Classic Cavus Foot Neuropathy
- Cavovarus Foot: Hindfoot varus driven by plantarflexed first ray.
- Coleman Block Test: Determines if hindfoot varus is forefoot driven (supple).
- Peroneus Brevis: First muscle affected (weak evertors).
- Surgical Principle: Soft tissue if supple, bony if rigid.
- CMT1A: Most common type, PMP22 duplication.
- “Coleman block test is essential
- “Weakness pattern: peroneus brevis first
- “Classic appearance: champagne bottle calves
- “Surgery depends on flexibility
Clinical Imaging
Imaging Atlas
Clinical Imaging
Imaging Atlas
Method: Stand on block, allow 1st ray to drop. Eliminates forefoot pronation effeft.
Corrects: Hindfoot varus resolves. Pathology: Forefoot-driven (Plantarflexed 1st Ray). Treatment: Soft tissue procedures.
No Correction: Hindfoot varus persists. Pathology: Fixed hindfoot deformity. Treatment: Bony surgery (Osteotomy/Fusion).
Weak: Peroneus Brevis/Tib Anterior. Strong: Tib Posterior/Peroneus Longus (Overpull causes deformity).
| Type | Pathology | NCV | Genetics |
|---|---|---|---|
| Demyelinating | Slow | PMP22 duplication (17p) | |
| Axonal | Normal | Various genes | |
| Severe demyelinating | Markedly slow | PMP22, MPZ, EGR2 | |
| X-linked | Intermediate | GJB1 |
CDColeman Block Test
Hook:C for Corrects = soft tissue. D for Doesn't = bony.
CMTCMT Muscle Weakness
Hook:PTI - Peroneus Brevis, Tibialis Anterior, Intrinsics.
FHCCavovarus Components
Hook:FHC - First ray, Hindfoot, Claws.
Overview/Epidemiology
Charcot-Marie-Tooth Disease (CMT) is the most common inherited peripheral neuropathy.
- Prevalence: 1 in 2,500.
- Inheritance: Autosomal dominant (most common), autosomal recessive, or X-linked.
- CMT1A: Most common subtype (70%). Caused by duplication of PMP22 gene on chromosome 17p.
- Presentation: Typically in childhood or adolescence with foot deformity, gait abnormalities.
Pathophysiology and Mechanism
Why Cavovarus Develops
- Peroneus brevis (evertor) is weaker than tibialis posterior (invertor) → varus.
- Tibialis anterior weakens → tibialis posterior and peroneus longus (plantarflexor of first ray) overpower → elevated arch.
- Plantarflexed first ray drives hindfoot into varus (forefoot-driven hindfoot varus).
- Intrinsic muscle weakness → claw toes.
Classic Clinical Appearance
- "Champagne bottle" or "inverted champagne bottle" calves (distal atrophy, normal proximal).
- High arched feet, claw toes.
- Wasting of intrinsic hand muscles later.
Classification Systems
CMT1 (Demyelinating)
- CMT1A: Most common. PMP22 duplication.
- CMT1B: MPZ (P0) mutation.
- NCV: Slow (often less than 38 m/s).
- Clinical: Onset in first decade. Progressive weakness.
Clinical Assessment
History:
- Age of onset.
- Progression.
- Family history.
- Foot pain, instability, calluses.
- Previous surgeries.
Physical Exam:
- Gait: Steppage gait (weak dorsiflexors).
- Muscle Bulk: Distal atrophy ("champagne bottle legs").
- Foot Deformity: Cavus, hindfoot varus, claw toes.
- Coleman Block Test: Essential.
- Flexibility: Assess hindfoot, first ray, ankle.
- Sensation: Diminished distally.
- Reflexes: Diminished or absent.
- Hands: Late involvement (claw hand).
Investigations
Nerve Conduction Studies (NCV):
- CMT1: Slow conduction (less than 38 m/s).
- CMT2: Normal or slightly slow.
Genetic Testing:
- Confirmatory. PMP22 duplication for CMT1A.
Imaging:
- Weight-bearing foot X-rays.
- Assess: Meary's angle (talo-first metatarsal angle), calcaneal pitch, hindfoot alignment.
Management Algorithm
Conservative Management
- Physiotherapy: Stretching, strengthening.
- AFO: Ankle-foot orthosis for weak dorsiflexors.
- Footwear: Accommodative shoes.
- Activity Modification: Avoid high-impact activities.
Surgical Techniques
Plantar Fascia Release
Indications: First ray plantarflexion contributing to cavus.
Technique: Medial incision. Release plantar fascia from calcaneus. May combine with other procedures.
Post-op: Weight bearing in orthotic.
Complications
- Context
- Common due to progressive disease
- Management
- Monitor, repeat surgery may be needed
- Context
- Valgus/planovalgus
- Management
- Avoid overcorrection
- Context
- Osteotomy or fusion
- Management
- Revise with bone graft
- Context
- After triple arthrodesis
- Management
- Expected
- Context
- Casts, braces, insensate areas
- Management
- Careful orthotic management
Postoperative Care
- Immobilization: Cast or boot for 6-12 weeks depending on procedure.
- Weight Bearing: Per procedure (typically NWB for osteotomies/fusions).
- Physiotherapy: ROM, strengthening after healing.
- Orthotics: Often needed long-term (AFO, custom insoles).
Outcomes/Prognosis
- Disease Progression: CMT is progressive. Orthopaedic issues may recur.
- Soft Tissue Procedures: Good results in supple feet; recurrence possible.
- Bony Procedures: More durable but sacrifice motion.
- Triple Arthrodesis: Definitive but stiff.
Evidence Base
- Identified a 1.5 Mb tandem duplication on chromosome 17p11.2 (PMP22 locus) completely linked to CMT1A
- Established CMT1A as a gene-dosage disorder caused by PMP22 over-expression
- Duplication detectable across different ethnic origins, enabling DNA-based diagnosis
- Authoritative review confirming CMT as the most common inherited neuromuscular disorder with marked genotypic and phenotypic heterogeneity
- Diagnosis rests on clinical pattern, inheritance, nerve-conduction studies and DNA testing
- No disease-modifying drug exists; rehabilitation and surgery for skeletal deformity remain the mainstays of care
Viva Scenarios
Practise clinical reasoning and management decisions out loud
“14-year-old with bilateral cavus feet, claw toes, and weak ankle dorsiflexion. Family history of similar foot shape. Coleman block test shows hindfoot varus corrects when the first ray is allowed to drop.”
This presentation is consistent with **Charcot-Marie-Tooth disease**. The Coleman block test showing correction indicates **forefoot-driven hindfoot varus** which is supple. Management: **Soft tissue surgery**. I would perform a **plantar fascia release**, **peroneus longus to brevis transfer**, **first metatarsal dorsiflexion osteotomy**, and **claw toe correction** (Jones procedure). I would counsel the family that the disease is progressive and recurrence is possible. Long-term orthotic use and monitoring are essential.
“Same patient 10 years later. Now 24. Feet have become rigid. Coleman block test negative. Recurrent ankle sprains, lateral foot pain.”
The deformity has progressed to become **rigid**. The negative Coleman block confirms this. Soft tissue procedures alone will not be sufficient. Management: **Bony surgery**. I would perform a **Dwyer osteotomy** (lateral closing wedge calcaneal osteotomy) to correct the fixed hindfoot varus. If the first ray is still plantarflexed, a **first metatarsal osteotomy** is needed. In very severe cases, a **triple arthrodesis** may be required, but I would try to preserve motion if possible. Claw toe correction as needed.
“How do you classify CMT?”
CMT is classified based on **nerve conduction velocity (NCV)** and **genetics**. **CMT1** is demyelinating with slow NCV (less than 38 m/s) - CMT1A (PMP22 duplication) is the most common. **CMT2** is axonal with normal NCV. **CMT3** (Dejerine-Sottas) is a severe infantile demyelinating form. **CMTX** is X-linked. Genetic testing is confirmatory.
MCQ Practice Points
Q: The most common CMT type is caused by which genetic abnormality? A: PMP22 duplication (CMT1A) on chromosome 17p.
Q: What does a positive Coleman block test indicate? A: The hindfoot varus is forefoot-driven and supple. Soft tissue surgery is appropriate.
Q: Which muscle is affected first in CMT? A: Peroneus brevis (weak eversion → varus).
Q: What osteotomy corrects fixed hindfoot varus? A: Dwyer osteotomy (lateral closing wedge calcaneal osteotomy).
Q: What tendon transfer is done to address weak eversion in CMT? A: Peroneus longus to peroneus brevis transfer.
Q: What procedure is used for claw toes in CMT? A: Jones procedure (EHL transfer to first metatarsal head with IP fusion).
Guidelines, Registries & Global Practice
Global epidemiology
- CMT is the most common inherited neuromuscular disorder worldwide, prevalence approximately 1 in 2,500 across populations (Pareyson and Marchesi, Lancet Neurol — PubMed).
- CMT1A (PMP22 duplication) accounts for the majority of demyelinating disease; CMTX (GJB1) is the second most common overall. Subtype frequency varies modestly by region and by founder effects.
Guidance, side by side
- Emphasis
- Diagnostic algorithm: clinical pattern + inheritance + NCS, then targeted genetics (PMP22 first); no disease-modifying drug recommended
- Emphasis
- Cavovarus work-up is a neurological diagnosis; flexibility-based (Coleman block) operative algorithm — soft tissue if supple, osteotomy/fusion if rigid
- Emphasis
- Multidisciplinary neuromuscular pathway; unilateral or rapidly progressive cavus mandates neuraxis MRI
- Emphasis
- High-quality evidence that ascorbic acid does not modify CMT1A (Gess et al. — PubMed); rehabilitation and surgery remain the mainstays
Registries and trial networks
- No arthroplasty-style implant registry applies. The Inherited Neuropathies Consortium (INC) and CMT-TRIAAL/CMT-TRAUK networks provide natural-history and trial data using validated outcomes (CMT Neuropathy Score, CMTPedS in children).
High- vs limited-resource practice variation
- Well-resourced settings: confirmatory genetic panels, gait-lab assessment, custom AFOs, joint-sparing reconstruction with intra-operative pedobarography/fluoroscopy.
- Limited-resource settings: diagnosis is clinical and electrophysiological; management leans on bracing and a smaller menu of durable bony procedures (Dwyer osteotomy, triple arthrodesis) where follow-up and orthotic supply are constrained. The flexibility-based principle is universal regardless of resources.
GENETICS
- CMT1A: PMP22 duplication
- Most common inherited neuropathy
- Autosomal dominant
- 1 in 2,500
CLINICAL
- Cavovarus foot
- Claw toes
- Champagne bottle calves
- Weak dorsiflexion
COLEMAN TEST
- Positive (corrects) = Supple
- Negative = Rigid
- Guides surgery
- Essential exam finding
SUPPLE FOOT SURGERY
- Plantar fascia release
- First MT osteotomy
- Peroneus longus to brevis
- Jones procedure
RIGID FOOT SURGERY
- Dwyer osteotomy
- Calcaneal closing wedge
- Triple arthrodesis
- Tendon transfers
EXAM PEARLS
- Peroneus brevis first affected
- NCV: CMT1 slow, CMT2 normal
- Progressive disease
- Recurrence common
Self-Assessment Quiz
Differential Diagnosis
A cavovarus foot is a neurological diagnosis until proven otherwise. CMT is the most common cause, but the examiner will expect you to exclude the alternatives below. Bilateral symmetric deformity with a positive family history points to CMT; a unilateral or rapidly progressive cavus foot should prompt MRI of the neuraxis to exclude a tethered cord or intraspinal tumour.
| Condition | Lesion type | Laterality / pattern | Discriminating features |
|---|---|---|---|
| Peripheral neuropathy (LMN) | Bilateral, symmetric, slowly progressive | Family history, distal atrophy, absent reflexes, slow NCV (CMT1), PMP22 duplication | |
| Spinocerebellar degeneration | Bilateral, progressive | Cerebellar ataxia, dysarthria, hypertrophic cardiomyopathy, diabetes, GAA repeat in FXN | |
| UMN / mixed | Often unilateral or asymmetric | Back signs, bowel/bladder change; mandates whole-spine MRI — especially if unilateral | |
| UMN (cerebral) | Hemiplegic or diplegic | Spasticity, brisk reflexes, clonus, birth history; equinovarus more typical than pure cavovarus | |
| Anterior horn cell (LMN) | Asymmetric, flaccid | Non-progressive after acute illness, preserved sensation, endemic exposure | |
| Structural | Unilateral or bilateral | Normal neurology, history of CTEV; diagnosis of exclusion |
Controversies and Areas of Uncertainty
- Timing of surgery in children. Whether to intervene early (while flexible, hoping to prevent fixed deformity) or to delay until growth and deformity stabilise is unresolved. Early soft-tissue balancing may need revision as the progressive neuropathy continues; there are no randomised data to settle the question.
- Soft-tissue reconstruction vs early arthrodesis. Long-term joint-sparing series (Ward et al. — PubMed) show durable function and lower arthritis rates than historical triple-arthrodesis cohorts, shifting practice toward osteotomy-and-transfer reconstruction. The threshold at which a foot is "too rigid" to reconstruct, and the role of midfoot tarsectomy versus triple fusion, remains debated.
- Tibialis posterior transfer. Routine transfer of tibialis posterior to the dorsum to address dropfoot is favoured by some surgeons and avoided by others who prefer to preserve it and use an AFO, given the progressive nature of the weakness.
- No disease-modifying therapy. Despite promising animal data, no drug (including ascorbic acid, definitively negative in Cochrane meta-analysis) alters the neuropathy. Gene-targeted therapies for CMT1A (PMP22 down-regulation) are in early-phase trials and are not yet standard of care.
- Genetic testing strategy. With next-generation sequencing panels now covering scores of CMT genes, the role of staged single-gene testing (PMP22 first) versus upfront panel testing is evolving and resource-dependent.