Multiple Osteochondroma

Also known as

  • hereditary multiple osteocartilaginous exostoses
  • diaphyseal aclasis
Multiple Osteochondroma, radiograph of multiple osteochondromas around the knee
Radiograph of multiple osteochondromas around the knee. Image by Bovée JV., Wikimedia Commons, CC BY 2.0.
Histology of an osteochondroma at medium power
Histology of an osteochondroma at medium power. Image by Sarahkayb, Wikimedia Commons, CC BY-SA 4.0.

Epidemiology

  • Rare

Aetiology

  • Autosomal dominant. 
  • Associated with mutations in EXT1 & EXT2, which leads to a maldistribution of Indian hedgehog in the extracellular matrix
  • Usually associated with short stature

Clinical

  • Clinically multiple osteochondromas.
  • Lesions are radiologically, grossly & microscopically similar to solitary osteochondromas
  • A good sign is defects of tubulation of the long bones, particularly around the femoral neck

Malignant Transformation

  • THERE IS A MUCH HIGHER RATE OF MALIGNANT TRANSFORMATION – AROUND 2-5%
  • The presence of a thick, active cartilage cap on an exostosis in a skeletally mature individual alerts one to the possibility of malignant transformation

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.