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Updated: Oct 27 2021

Myositis Ossificans

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  • summary
    • Myositis Ossificans is a reactive soft tissue bone-forming process that commonly occurs following a traumatic event to soft tissues.
    • The condition typically presents in patients between ages 15 and 35 who develop pain, tenderness, swelling, and decreased range of motion following localized trauma.
    • Diagnosis is made with radiographs showing peripheral bone formation with central lucent area within soft tissues. 
    • Treatment is usually observation as lesions typically resolve over time. Surgical excision is indicated for lesions that remain persistently symptomatic.  
  • Epidemiology
    • Demographics
      • most common in young active males (15 to 35 years old)
    • Anatomic locations
      • quadriceps, brachialis and gluteal muscles
  • Etiology
    • A form of heterotopic ossification that is the result of
      • direct trauma
      • intramuscular hematoma
        • most common location is the diaphysis of long bones
    • Associated conditions
      • Must differentiate from tumors
      • Fibrodysplasia ossificans progressiva (FOP) is a rare subtype of heterotopic ossification
        • involves mutation of the ACVR1 gene (activin A type I receptor gene, a BMP type-1 receptor)
    • Genetics
      • almost always a posttraumatic condition
  • Presentation
    • Symptoms
      • pain, tenderness, swelling and decreased range of motion that usually presents within days of the injury
        • pain and size of the mass decrease with time
      • mass increases in size over several months (usually 3 to 6 cm)
        • after the mass stops growing, it becomes firm
    • Physical exam
      • palpable soft tissue mass
      • restricted range of motion
  • Imaging
    • Radiographs
      • peripheral bone formation with central lucent area
      • may appear as "dotted veil" pattern
    • MRI with gadolinium
      • rim enhancement is seen within the first 3 weeks
    • CT scan
      • lesion has an eggshell appearance
  • Histology
    • Characteristic histology shows zonal pattern
      • periphery of lesion
        • mature trabeculae of lamellar and woven bone
        • calcification seen on xray
      • center of the lesion
        • irregular mass of immature fibroblasts
        • cartilage component may be present
        • (no calcification seen on xray)
        • no cellular atypia seen
  • Treatment
    • Nonoperative
      • rest, range of motion exercises, and activity modification
        • passive stretching is contraindicated (makes it worse)
        • physical therapy
          • utilized to maintain range of motion
      • radiographic monitoring
        • obtained to confirm maturation of the lesion
    • Operative
      • surgical excision
        • indicated only if it remains a problem after it matures
        • do not operate in acute phase, wait at least six months
          • excision of the lesion within 6 to 12 months predisposes to local recurrence
  • Prognosis
    • Usually self limiting
      • mass usually begins to decrease in size after 1 year
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