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Introduction
  • A hereditary motor sensory neuropathy (HMSN) that has two forms resulting in muscles weakness and sensory changes
  • Epidemiology
    • most common inherited neurological disease
    • 1:2,500
  • Pathophysiology
    • combination of motor and sensory disturbances as a result of nerve damage
      • motor involvement more profound than sensory
    • affected muscles become weak 
      • peroneus brevis
      • tibialis anterior
      • intrinsic muscles of hand and foot
  • Genetics
    • inheritance
      • autosomal dominant (most common)
      • may also be
        • autosomal recessive
        • X-linked
    • mutations
      • duplication on chromosome 17 
        • codes for peripheral myelin protein 22 (PMP 22
        • X-linked connexin 32
  • Orthopedic manifestations  
    • pes cavus 
    • hammer toes 
    • hip dysplasia 
    • scoliosis
Classification
 
 Classification of CMT
Type I demyelinating condition that slows nerve conduction velocity 
Characteristics:
   1. autosomal dominant
   2. onset in first or second decade of life
   3. most commonly leads to cavus foot
Type II Direct axonal death caused by Wallerian degeneration (not demyelination) 
Characteristics:
   1. Usually less disabled than Type I
   2. onset in second decade of life or later
   3. most commonly leads to flaccid foot
 
Presentation
  • Symptoms
    • lateral foot pain 
    • sensory deficits are variable
    • clumsiness
    • frequent ankle sprains
    • difficulty climbing stairs
  • Physical exam
    • lower extremity
      • rigid cavovarus foot (similar to Freidreich's ataxia) with hammer toes or clawing of toes 
      • atrophied EDB and EHB
      • calf atrophy
      • weak dorsiflexion and eversion due to weak tib ant and peroneals (foot drop during swing phase)
      • lower limb areflexia
      • Coleman block test
        • test to evaluate flexibility of hindfoot
          • flexible hindfoot will correct to neutral when block placed under lateral aspect of foot
          • a rigid hindfoot will not correct into neutral
    • upper extremity
      • intrinsic wasting of hands
Studies
  • EMG
    • low nerve conduction velocities with prolonged distal latencies are noted in peroneal, ulnar, and median nerves
  • Genetic Testing
    • DNA analysis
      • PCR analysis used to detect peripheral myelin protein 22 (PMP22) gene mutations
    • chromosomal analysis
      • duplication on chromosome 17 seen in autosomal dominant (most common) form
Cavus Foot Deformity
  • Introduction
    • plantar flexed 1st ray is initial deformity 
    • cavus caused by peroneus longus (normal) overpower weak tibialis anterior  
    • varus caused by tibialis posterior (normal) overpowering weak peroneus brevis 
  • Treatment
    • follows similar treatment principals to cavovarus foot
    • nonoperative
      • stretching, strengthening, and orthotics
        • indications
          • as initial management of a young patient
        • modalities
          • stretching & strengthening
            • should focus on mobilization and strengthening of the weakening muscular units (peroneals, tibialis anterior)
          • orthotics 
            • includes accommodative inserts and orthotic devices for flexible deformity
            • in a flexible deformity the orthosis should post lateral forefoot and the lateral heel   
            • AFOs for foot drop
    • operative
      • plantar fascia release, tibialis posterior or peroneus longus tendon transfer, ± TAL, ± 1st metatarsal dorsiflexion osteotomy
        • indications
          • flexible hindfoot cavus deformities (normal Coleman block test)
          • surgical intervention should be delayed until progression of the deformity begins to cause symptoms and/or weakness of the muscular units, resulting in contractures of the antagonistic muscle units.
        • technique
          • tendon transfer (two method depending on involved muscels)
            • posterior tibialis transfer to dorsum of foot to improve foot drop (augment weak tibialis anterior)   
            • peroneus longus transfer to peroneus brevis (if peroneus longus is normal)
      • calcaneal valgus producing osteotomy
        • indications 
          • rigid hindfoot cavus deformities (abnormal Coleman block test)
        • technique
          • combine with soft tissue procedure discussed above, and dorsiflexion 1st metatarsal osteotomy
      • triple arthrodesis 
        • indications
          • severe rigid deformities
          • may be helpful in select cases but is falling out of favor
      • 1st metatarsal osteotomy and transfer of EHL to neck of 1st MT 
        • indications
          • if there is hallux clawing combined with cavus foot
Claw Toes Deformity
  • Introduction
    • ankle dorsiflexion weakness may result in the recruitment of toe extensors for assistance
      • in the setting of intrinsic muscle weakness, increased toe extensor activity can lead to claw toe deformity
  • Treatment
    • operative
      • Jones procedure 
        • indications
          •  for symptomatic claw toe deformity which has failed non-operative measures
        • technique
          • transfers extensor tendons of the great and lesser toes through the bone into the metatarsal neck
          • goal is to increase contributions to ankle dorsiflexion and decrease clawing in order to relieve pain on the dorsum of the toes
Hip dysplasias
  • Introduction
    • hip dysplasia is sometimes associated with CMT
      • may present during adolescence in ambulatory patients
  • Treatment
    • pelvic osteotomy
      • indications
        • end-stage osteoarthritis
      • outcomes
        • higher rate of sciatic nerve palsy after surgery
Scoliosis
  • Introduction
    • often occurs in children with CMT
    • characteristic left thoracic and kyphotic curve distinguish from idiopathic scoliosis
  • Treatment
    • nonoperative
      • bracing
        • indications
          • bracing rarely effective
    • operative
      • fusion and instrumentation
        • indications
          • progressive deformity
 

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