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Multiple Hereditary Exostoses

Diaphyseal Aclasis
 

  • Inheritance
    • Autosomal dominant
  • Age of onset
    • Discovered between 2 and 10 years
  • Male predominance = 2:1
  • Pathology
    • Ectopic cartilaginous rest in metaphysis and a defect in periosteum produces exostoses
    • Cap of hyaline cartilage over bony protuberance
    • Cortex and cancellous bone of exostosis is contiguous to host bone
  • Clinical
    • Usually painless mass near joints
    • Tendons, blood vessels, nerves may be impaired
    • Mechanical limitation of joint movement may occur
  • Location
    • Multiple
    • Usually bilateral
    • Common sites are knee, elbow, scapula, pelvis, ribs

  • Site
    • Metaphyses of long bones near epiphyseal plate (distance to epiphyseal line increases with growth)
    • Always point away from joint and toward center of shaft
    • Occasionally small punctate calcifications are seen in cartilaginous cap
  • Other skeletal abnormalities may occur
    • Shortening of 4th and 5th metacarpals
    • Supernumerary fingers and/or toes
    • Madelung / reversed Madelung deformity
    • Dislocation of radial head
  • Prognosis
    • Exostosis begins in childhood
    • Stops growing when nearest epiphyseal center fuses
  • Complications
    • Malignant transformation to chondrosarcoma in <5%
      • Iliac bone commonest site
      • Look for growth with irregularity of contour and fuzziness of margin
      • Sudden painful growth spurt
    • Cord compression secondary to involvement of posterior spinal elements

 

From Dahnert

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