Updated: 6/16/2021

Metaphyseal Chondrodysplasia

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  • summary
    • Metaphyseal Chondrodysplasia is a heterogeneous group of congenital disorders caused by variety of mutations leading to metaphyseal changes of the tubular bones with normal epiphyses. Patients present with short-limb dwarfism characterized by genu varum, coxa vara, and spinal abnormalities. 
    • Diagnosis is made based on family history associated with typical radiographic and clinical features. No commercially available diagnostic test exists due to the variety of genetic mutations.
    • Treatment involves a multidisciplinary approach to improve and maintain function. Surgical spinal fusion is indicated in patients with atlantoaxial instability.
  • Epidemiology
    • Incidence
      • skeletal dysplasias occur at a rate of 2 to 3 newborns per 10,000 births
  • Etiology
    • 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
      Characteristics
      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 recessive
      • 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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