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  • A hereditary motor sensory neuropathy (HMSN) that has two forms resulting in muscles weakness and sensory changes
  • Epidemiology
    • most common inherited progressive peripheral neuropathy
    • 1:2,500
  • Pathophysiology
    • HMSN Type I: abnormal myelin sheath protein is the basis of this degenerative neuropathy. This results in a combination of motor and sensory disturbances. 
      • motor involvement is typically more profound than sensory
    • affected muscles become weak 
      • peroneus brevis
      • tibialis anterior
      • intrinsic muscles of hand and foot
    • HSMN Type 2: intact myelin sheath with wallerian axonal degeneration that results in mild sensory and motor conduction velocities. 
  • Genetics
    • inheritance
      • autosomal dominant duplication of chromosome 17 (most common)  
        • codes for peripheral myelin protein 22 (PMP 22) (most common) 
        • X-linked connexin 32
      • may also be
        • autosomal recessive
        • X-linked
  • Orthopedic manifestations  
    • pes cavus 
    • hammer toes 
    • hip dysplasia 
    • scoliosis
 Classification of CMT
Type I demyelinating condition that slows nerve conduction velocity 
   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) 
   1. Usually less disabled than Type I
   2. onset in second decade of life or later
   3. most commonly leads to flaccid foot
  • 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
  • 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
  • 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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