Pes Cavus & Charcot Marie Tooth Disease

Epidemiology

  • Charcot-Marie-Tooth (CMT) is the most common inherited neuropathy.
  • Men > Women, but women have more severe symptoms.
  • Patients typically present in the 2nd or 3rd decade.

Inheritance Pattern

  • Autosomal Dominant (most common) – defect on chromosome 17 affecting peripheral myelin protein 22 (PMP22).
  • Sex-linked recessive & autosomal recessive forms present earlier and are more severe.
  • Predictors of severity:
    • Early presentation (<10 years)
    • Autosomal or sex-linked recessive pattern
    • Female gender
    • Associated sensory deficit (causes ulcers as in diabetes)

Hereditary Motor Sensory Neuropathies (HMSN)

Aetiology

  • Autosomal Dominant disorder causing predominantly distal motor & sensory deficits.
  • Family history is crucial for diagnosis.

Types of HMSN (7 types; most common below)

HMSN 1 (CMT – Myelopathic/Hypertrophic)

  • More common
  • Onset: 10-20 years
  • Demyelination of nerves
  • Nerve conduction studies: Prolonged latencies, reduced velocities
  • Absent reflexes

HSMN 2 (CMT – Neuropathic)

  • Less common
  • Onset: 20-30 years
  • Wallerian degeneration without demyelination
  • EMG near normal
  • Reflexes present

Clinical Features of Both

  • Motor > Sensory involvement
  • Most affected muscles: Peronei & Tibialis Anterior
  • Foot deformities: Cavus, Cavovarus, Hammer toes
  • Surgical goals: Maintain flexibility via transfers/osteotomies
  • Avoid fusions where possible (young patients)
  • Hip dislocation & scoliosis rare
  • Intrinsic wasting of hands

HMSN 3 (Dejerine-Stotta Disease)

  • Autosomal Recessive (AR)
  • Onset: Infancy
  • Severe manifestations:
    • Foot drop
    • Scoliosis
    • Difficulty ambulating

Aetiology of Pes Cavus

  • CMT is predominantly a motor neuropathy causing muscle imbalance.
  • Pes Cavus can arise from any neurological condition causing imbalance.
  • Often no identifiable neurological cause.
  • Usually symmetrical.
  • Weakness primarily in:
    • Peroneus Brevis, Tibialis Anterior, Intrinsics

Deformities & Muscle Weakness

Cavus Deformity

  • Plantar flexion of 1st ray is the driving force.
  • Peroneus Longus overpowers Tibialis Anterior.
  • Windlass mechanism exacerbates deformity.

Varus Deformity

  • Two causes:
    1. Plantar flexed 1st ray → Pronated forefoot.
    2. Tripod effect → Hindfoot varus to balance the foot.
  • Weak Peroneus Brevis overpowered by TP → Net inversion.

Equinus Deformity

  • Weak Tibialis Anterior → Gastrosoleus dominance.

Claw Toes

  • EDL compensates for weak TA → Overuse causes clawing.
  • Intrinsics weak, FDL relatively spared → MTPJ hyperextension, PIP/DIPJ flexion.

Clinical Features

History

  • Chief complaints: Deformity & stiffness > Pain or paraesthesia.
  • Difficulty on uneven ground & sports.
  • Family history common.
  • Plantar pain (metatarsalgia).

Examination

  • Deformities: Cavus foot, toe clawing, hindfoot varus.
  • Coleman block test – Assess hindfoot flexibility.
  • Silverskold test – Assess Equinus.
  • Painful joints? – Indicates arthrosis.
  • Stork legs: Thin calves, normal thigh girth.
  • Sensory changes:
    • Mild proprioception & vibration deficits.
    • 2-point discrimination may be affected.
  • Muscle Power: Assess PL, PB, TA, TP, etc.
  • Screen for neurological issues: Spine, skin, gait.
  • Advanced cases: Intrinsic minus hand deformity.

Investigations

X-Ray (Standing AP & Lateral)

  • Lateral: High arch, cuboid in profile.
  • Calcaneal pitch >30° (abnormal).
  • Positive Meary’s angle (>5° abnormal).
  • AP: Posteriorly displaced fibula (external tibial rotation).

MRI

  • Selective use – Asymmetric cases, other neurological symptoms.

Genetic Testing

  • For family screening.

Nerve Conduction Studies & EMG

  • EMG useful as motor nerves primarily affected.
  • Demyelination → Slowed conduction velocities.

Management

Non-Operative

  • Footwear modifications & AFOs.
  • Does not alter disease course.
  • Delays surgery until symptomatic deformities arise.

Surgical Treatment

  • Correct deformities based on flexibility & arthrosis.

1st Ray Plantarflexion

  • Dorsal closing wedge osteotomy.
  • Peroneus Longus to Peroneus Brevis transfer.

Cavus Deformity

  • Plantar fascia release.
  • TP transfer to dorsum via interosseous membrane (IOM).

Hindfoot Varus

  • PL to PB transfer.
  • Lateral closing wedge calcaneal osteotomy (Dwyer).
  • Lateral calcaneal slide osteotomy.

Equinus Deformity

  • Usually corrects after other deformities are addressed.
  • TA lengthening reserved for last correction.

Claw Toes

  • Girdlestone-Taylor split FDL to EDL transfer.
  • Weil osteotomy if correction is incomplete.
  • MTPJ release, PIPJ excision arthroplasty.

Big Toe Clawing

  • Jones Procedure – IPJ fusion & EHL transfer to 1st MT dorsum.

Arthrodesis (Last Resort)

  • Triple arthrodesis if fixed, painful deformities.
  • Avoid as long as possible (young patients).

In Reality

  • Most cases require a combination of osteotomies & tendon transfers.
  • Patients often still need orthoses post-surgery.
  • TP IOM transfer helps but may not fully prevent drop foot.
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