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

Multiple Hereditary Exostoses. Multiple exostoses are seen arising from the proximal and distal tibias and fibulas. The bones are dysplastic in appearance.