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.