High Yield Overview

Charcot-Marie-Tooth Disease

The Classic Cavus Foot Neuropathy

1 in 2,500Prevalence

CMT Type 1A (PMP22)Most Common

Cavovarus FootClassic Deformity

Determines surgic approachColeman Block Test

CMT Classification

CMT1

PatternDemyelinating (slow NCV). CMT1A is most common.

TreatmentVariable progression

CMT2

PatternAxonal (normal NCV).

TreatmentOften milder

CMT3 (Dejerine-Sottas)

PatternSevere infantile demyelinating.

TreatmentSevere disability

CMTX

PatternX-linked.

TreatmentVariable

Critical Must-Knows

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.

Examiner's Pearls

"
Coleman block test is essential
"
Weakness pattern: peroneus brevis first
"
Classic appearance: champagne bottle calves
"
Surgery depends on flexibility

Clinical Imaging

Imaging Gallery

Clinical phenotype. The patient shows a scapuloperoneal pattern of muscle wasting and weakness with pectoral wasting and scapular winging (A, C). The arms cannot be lifted over the horizontal level (A — Clinical phenotype. The patient shows a scapuloperoneal pattern of muscle wasting and weakness with pectoral wasting and scapular winging (A, C). The Credit: Schreiber O et al. via BMC Med. Genet. via Open-i (NIH) (Open Access (CC BY))

MR imaging. Whole-body MRI shows nearly complete fatty atrophy of the tibialis anterior muscles and the Mm. gastrocnemii, as well as moderate fatty replacement of muscle tissue in the soleus muscle (A — MR imaging. Whole-body MRI shows nearly complete fatty atrophy of the tibialis anterior muscles and the Mm. gastrocnemii, as well as moderate fatty reCredit: Schreiber O et al. via BMC Med. Genet. via Open-i (NIH) (Open Access (CC BY))

Muscle biopsy. (A) H&E staining of a muscle biopsy of the left anterior tibial muscle with mild myopathic changes indicated by muscle fiber splitting and increase in endomysial connective tissue. — Muscle biopsy. (A) H&E staining of a muscle biopsy of the left anterior tibial muscle with mild myopathic changes indicated by muscle fiber splittCredit: Schreiber O et al. via BMC Med. Genet. via Open-i (NIH) (Open Access (CC BY))

Clinical Imaging

Imaging Gallery

Radiological angle measurements for cavovarus foot assessment — 10-panel composite showing weight-bearing lateral foot radiograph measurements for cavovarus deformity assessment: (1) Lateral talo-first metatarsal angle, (2) Metatarsal stacking angle, (3) AP talo-first metatarsal angle, (4) Lateral calcaneal-first metatarsal angle, (5) Naviculocuboid overlap, (6) Talonavicular coverage angle, (7) Medial-lateral column ratio, (8) Calcaneal pitch, (9) Tibiocalcaneal angle, (10) Talocalcaneal angle.Credit: Joo SY et al., Ann Rehabil Med - CC BY

MRI showing fatty muscle atrophy in CMT — Whole-body MRI demonstrating characteristic muscle changes in CMT: (A) Coronal view showing near-complete fatty atrophy of tibialis anterior and gastrocnemius muscles bilaterally, (B-C) Axial slices showing fatty replacement of distal leg muscles - typical pattern of distal-predominant denervation.Credit: Schreiber O et al., BMC Med Genet - CC BY

Coleman Block Test

The Test

Method: Stand on block, allow 1st ray to drop. Eliminates forefoot pronation effeft.

Supple Deformity

Corrects: Hindfoot varus resolves. Pathology: Forefoot-driven (Plantarflexed 1st Ray). Treatment: Soft tissue procedures.

Rigid Deformity

No Correction: Hindfoot varus persists. Pathology: Fixed hindfoot deformity. Treatment: Bony surgery (Osteotomy/Fusion).

Muscle Balance

Weak: Peroneus Brevis/Tib Anterior. Strong: Tib Posterior/Peroneus Longus (Overpull causes deformity).

CMT Types

Type	Pathology	NCV
Demyelinating	Slow	PMP22 duplication (17p)
Axonal	Normal	Various genes
Severe demyelinating	Markedly slow	PMP22, MPZ, EGR2
X-linked	Intermediate	GJB1

Mnemonic

Coleman Block Test

Corrects

Forefoot driven, supple

Doesn't Correct

Rigid, needs bony surgery

Memory Hook:C for Corrects = soft tissue. D for Doesn't = bony.

Mnemonic

CMT Muscle Weakness

Peroneus Brevis

First affected

Tibialis Anterior

Then affected

Intrinsics

Claw toes develop

Memory Hook:PTI - Peroneus Brevis, Tibialis Anterior, Intrinsics.

Mnemonic

Cavovarus Components

First Ray Plantarflexed

Drives the varus

Hindfoot Varus

Secondary

Claw Toes

Intrinsic weakness

Memory 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

Complication	Context	Management
Recurrence	Common due to progressive disease	Monitor, repeat surgery may be needed
Overcorrection	Valgus/planovalgus	Avoid overcorrection
Nonunion	Osteotomy or fusion	Revise with bone graft
Stiffness	After triple arthrodesis	Expected
Pressure Sores	Casts, braces, insensate areas	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

Landmark

📚 Coleman and Chesnut

Key Findings:

Described the Coleman block test
Forefoot-driven hindfoot varus
Guides surgical decision-making

Clinical Implication: Coleman block test is essential.

Source: CORR 1977

Landmark

📚 Dwyer

Key Findings:

Described lateral closing wedge calcaneal osteotomy
Corrects fixed hindfoot varus
Simple and effective

Clinical Implication: Dwyer osteotomy for rigid varus.

Source: JBJS Br 1959

Level IV

📚 Ward et al

Key Findings:

Long-term outcomes of cavus foot surgery
Recurrence is common
Multiple procedures often needed

Clinical Implication: Counsel patients about recurrence.

Source: Foot Ankle Int 2008

Review

📚 Refshauge et al

Key Findings:

Comprehensive review of CMT
Highlights foot deformity as major issue
Multidisciplinary care recommended

Clinical Implication: Multidisciplinary approach is key.

Source: Lancet Neurol 2016

Systematic Review

📚 Burns et al

Key Findings:

Review of interventions for CMT
Limited high-quality evidence
Orthoses and surgery are mainstays

Clinical Implication: Evidence base is limited but surgery is effective.

Source: Cochrane 2015

Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

The Adolescent with Cavus Feet

EXAMINER

"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."

EXCEPTIONAL ANSWER

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.

KEY POINTS TO SCORE

Coleman block positive = supple

Soft tissue surgery appropriate

Progressive disease - recurrence possible

COMMON TRAPS

✗Doing a triple arthrodesis in a supple foot

✗Ignoring the first ray

LIKELY FOLLOW-UPS

"What is the most common genetic cause of CMT?"

VIVA SCENARIOStandard

Rigid Cavovarus Foot

EXAMINER

"Same patient 10 years later. Now 24. Feet have become rigid. Coleman block test negative. Recurrent ankle sprains, lateral foot pain."

EXCEPTIONAL ANSWER

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.

KEY POINTS TO SCORE

Coleman block negative = rigid

Bony surgery (Dwyer) needed

Triple arthrodesis for severe cases

COMMON TRAPS

✗Attempting soft tissue surgery only

✗Not addressing all components

LIKELY FOLLOW-UPS

"What are the disadvantages of triple arthrodesis?"

VIVA SCENARIOStandard

CMT Classification

EXAMINER

"How do you classify CMT?"

EXCEPTIONAL ANSWER

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.

KEY POINTS TO SCORE

CMT1 = demyelinating, slow NCV

CMT2 = axonal, normal NCV

CMT1A is most common

COMMON TRAPS

✗Confusing pathology with NCV findings

LIKELY FOLLOW-UPS

"What gene is mutated in CMT1A?"

MCQ Practice Points

Pathology MCQ

Q: The most common CMT type is caused by which genetic abnormality? A: PMP22 duplication (CMT1A) on chromosome 17p.

Clinical MCQ

Q: What does a positive Coleman block test indicate? A: The hindfoot varus is forefoot-driven and supple. Soft tissue surgery is appropriate.

Muscle MCQ

Q: Which muscle is affected first in CMT? A: Peroneus brevis (weak eversion → varus).

Surgery MCQ

Q: What osteotomy corrects fixed hindfoot varus? A: Dwyer osteotomy (lateral closing wedge calcaneal osteotomy).

Tendon Transfer

Q: What tendon transfer is done to address weak eversion in CMT? A: Peroneus longus to peroneus brevis transfer.

Claw Toes

Q: What procedure is used for claw toes in CMT? A: Jones procedure (EHL transfer to first metatarsal head with IP fusion).

Australian Context

Genetic Testing: Available through clinical genetics services.
Orthopaedic Care: Managed at pediatric orthopaedic centers.
Orthotics: Custom AFOs provided through allied health.
Natural History: Counsel patients about progressive nature.