Duchene Muscular Dystrophy

  • Single gene defect on short arm of the X chromosome
  • X linked recessive
  • +ve family history in 65% (hence high new mutation rate)
  • 1:3500 live male births
  • 1/3 new mutant

Clinical

  • evident by 3-6 years
  • clumsiness, weakness
  • inability to or difficulty with running & climbing stairs
  • weakness especially effects the proximal muscle groups
  • pseudohypertrophy of the calf
  • cardiac involvement including dysrhythmia, RVH
  • mild to moderate mental retardation is common
  • death usually secondary to respiratory insufficiency
  • Gait
    • weak gluteal muscle
    • hyperlordotic, waddling gait
    • inversion of the foot (tib posterior involved late)
  • Meyeron Sign – child slips through truncal grasp
  • Gower Sign
  • Ober test for ITB contracture
  • Achilles tendon contracture
  • Children lose ambulation ~ 10 years
  • Most develop a spinal deformity

Investigations

  • CPK – marked elevation in early stages, 200-300X normal but decreases as disease progresses
  • CPK is also elevated in female carriers
  • EMG – reduced amplitude & polyphasic
  • Biopsy – degeration & loss of fibres which are replaced by connective tissue & fat
  • Genetics
    • DM – no dysrophin
    • Becker – abnormal dystrophin

Treatment

Orthopaedic Concerns

  • Decreased ambulation
  • Soft tissue contracture
  • Spinal deformity

Nonoperative

Physio – may be helpful in preventing contractures
Bracing – KAFO & AFO may be helpful in flexible deformity

Operative

  • Release of Contractures
    • Indicated if there is difficulty with ambulation or ADL
    • Achilles – lengthened & in nonambulatory consider percutaneous lengthening
    • Equinovarus – lengthen achilles & then transfer the tibialis posterior through the membrane if the foot is flexible
    • Knee flexion contracture – lengthen hamstrings, possible release of ITB
    • Hip Flexion – release sartorius, rectus femoris & tensor fascia lata
  • Scoliosis Treatment
    • ~ 95 % of patients develop a scoliosis
    • generally developed at time of cessation of walking
    • rapidly progressive
    • fuse when > 20°
    • Other Indictions
      • Scoliosis of 30° or a FVC of 40%
    • upper thoracic to the pelvis  is conservative – Galveston = Luque to the pelvis
    • FVC drops starting at ~ 10 years of age by 4% / year & 4% / 10°
    • Should fuse early before progresses
    • Improves quality of life
    • Not proven to ↑ the quality of life