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