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Introduction
  • Heterogeneous group of disorders characterized by metaphyseal changes of the tubular bones with normal epiphyses 
  • Epidemiology
    • incidence
      • skeletal dysplasias occur at a rate of 2 to 3 newborns per 10,000 births
  • Pathophysiology
    • metaphyseal dysplasia involving the proliferative and hypertrophic zone of the physis (epiphysis is normal)
  • Genetics
    • three main subtypes
      • Jansen (rare, most severe form)
        • autosomal dominant
        • genetic defect in parathryoid hormone-related peptide (PTHrP)
      • Schmid (more common, less severe form)
        • autosomal dominant
        • genetic defect in type X collagen
      • McKusick
        •  autosomal recessive
        • most commonly occurs in Amish and Finnish populations
        • cartilage-hair dysplasia (hypoplasia of cartilage and small diameter of hair)
  • Associated conditions
    • birth defects
      • can be mimicked by teratogenic 
    • rickets
      • Schmid type often confused for rickets
Classification
 
Table of Metaphyseal Chondrodysplasias
Type
Genetics
Characteristic
Comments
Jansen's
  • autosomal dominant
  • defect in parathyroid hormone related peptide (PTHRP) receptor
  • mental retardation
  • short limbed dwarfism
  • wide eyes
  • monkey like stance
  • ostebulbous metaphyseal expansion of long bones seen on xray
Schmid's
  • autosomal dominant
  • defect in Type X collagen
  • short limbed dwarfism
  • excessive lumbar lordosis
  • severe thigh and leg bowing, genu varum
  • wrist swelling, elbow contractures
  • trendelenburg gait
  • diagnosed when patient older due to coxa vara and genu varum
  • often confused with Ricketts
McKusicks
  • autosomal reccessive
  • cartilage hair dysplasia (hair had small diameter)
  • atlantoaxial instability
  • ankle deformity due to fibular overgrowth
  • immunologic deficiency and increased risk for malignancy
  • seen in Amish population and in Finland
 
Presentation
  • Jansen type 
    • mental retardation
    • markedly-short limbed dwarfism with: 
      • wide eyes
      • monkey-like stance
      • hypercalcemia
  • Schmid type
    • often not diagnosed until older age due to marked coxa vara and genu varum
    • short-limbed dwarf involving:
      • Trendelenburg gait
      • predominate proximal femur involvement
      • increased lumbar lordosis
      • normal laboratory results
  • McKusick type
    • common associated with
      • atlantoaxial instability secondary to odontoid hypoplasia
      • ankle deformity due to fibular overgrowth
      • associated with:
        • abnormal immunocompetence
        • increased risk for malignancies
        • intenstinal malabsorption
        • megacolon
Imaging
  • Radiographs
    • Jansen type 
      • AP pelvis, hip, knee, and upper extremity radiographs   
        • reveals bulbous expansion of metaphysis
    • Schmid type
      • AP pelvis and hip radiographs
        • rule out coxa vara
      • standing lower extremity films
        • rule out genu varum
    • McKusick type
      • cervical AP, lateral, flexion and extension views
        • rule out atlantoaxial instability
      • ankle AP, oblique and lateral views
        • surveillance of potential distal fibular overgrowth
    • Metaphyseal dysplasia involving the proliferative and hypertrophic zone of the physis (epiphysis is normal)
Treatment
  • Operative
    • posterior atlantoaxial fusion
      • indications
        • atlantoaxial instability measuring 8 mm or more 
        • myelopathy
      • techniques
        • posterior instrumentation
    • valgus intertrochanteric osteotomy
      • indications
        • coxa vara angle <100 degrees
        • progressive coxa vara
        • symptomatic hip arthritis
      • techniques
        • valgus + extension osteotomy may help to decrease an associated hip flexion deformity
        • reconstructive measures may be indicated in patients with subluxation, hinge abduction, or osteoarthritis. 
        • open reduction and fixation of proximal femur and acetabulum to treat hip dislocations.
    • tibial osteotomies or hemiepiphysiodeses
      • indications
        • symptoms are severe
        • nonoperative modalities have failed
    • limb lengthening through a metaphyseal corticotomy
      • indications
        • controversial due to high rate of complications
 

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