Myositis Ossificans


  • Benign process characterised by heterotrophic ossification within large muscle groups
  • It is important because it often mimics more aggressive pathological conditions
  • Most common type is MO circumscripta – where new bone appears usually after trauma (common in young adults and paraplegics)
    • Other types/related conditions include MO progressiva (rare inherited disorder- progressive and ultimately fatal); panniculitis ossificans (similar to MOC but in subcut tissues)


  • MO is extraosseous bone formation without inflammation which occurs in muscle.  It has zonal organisation
    • Peripheral well organised mature/lamellar bone
    • Intermediate osteoid region
    • Central, immature non-ossified cellular focus
  • The histopathology can appear similar to osteosarcoma- so a clear history is important to avoid inappropriate management


  • Xray- lesion of dense peripheral calcification (other imaging may also be useful e.g. CT/MRI)


  • Observation if otherwise asymptomatic, surgery (resection) if painful


  • Painful, tender, enlarging mass, most commonly in the large muscles of the extremities, often following trauma

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