Clinical Time Course of Myositis Ossificans
Myositis ossificans (MO) is a benign condition characterized by heterotopic bone formation in soft tissues that typically progresses through distinct phases over several months, with most cases showing complete resolution within 6-24 months following appropriate management.
Types of Myositis Ossificans
- Myositis ossificans traumatica (MOT) or circumscripta is the most common form, developing after trauma such as contusions, strains, or repeated injury 1
- Myositis ossificans progressiva (also known as fibrodysplasia ossificans progressiva or FOP) is a rare genetic disorder with progressive heterotopic ossification 2
- Non-traumatic or pseudomalignant MO can develop without clear history of trauma, sometimes after prolonged immobilization 3
Clinical Time Course and Phases
Early Phase (1-2 weeks)
- Initial presentation includes pain, swelling, and decreased range of motion at the site of injury 1
- Clinically resembles a severe contusion with formation of a hematoma 1
- Diagnostic imaging may not show calcification at this stage 4
Intermediate Phase (2-4 weeks)
- Calcification begins to appear, typically at the periphery of the lesion 4
- Pain may persist with continued limitation in range of motion 1
- MRI during this phase may show edematous reaction in surrounding muscles 4
Mature Phase (4-6 months)
- Characteristic "zoning phenomenon" develops with mature bone formation at the periphery 4
- Radiographically visible calcified mass with well-defined borders 1
- Gradual decrease in pain and improvement in function 1
Resolution Phase (6-24 months)
- Most cases show gradual resorption of heterotopic bone over time 1
- Complete resolution may occur within 1-2 years with appropriate management 1
- Some cases may leave residual calcification or ossification 4
Diagnostic Evolution
- Early diagnosis is challenging as initial presentation mimics soft tissue injury 1
- Plain radiographs initially negative, with calcification becoming visible after 2-6 weeks 4
- CT scan shows characteristic peripheral mature bone formation with smooth contour well-separated from adjacent bone 3
- MRI can identify muscle inflammation and guide biopsy site selection if needed 5
Management Timeline
- Initial management (first 48-72 hours): Rest, ice, compression, and elevation (RICE) to minimize extension of the original injury 1
- Early phase (1-2 weeks): Continue RICE protocol with pain management 1
- Intermediate phase (2-4 weeks): Begin gentle, painless range-of-motion exercises to help restore mobility 1
- Late phase (>4 weeks): Gradual return to activities with protective padding to prevent additional trauma 1
Special Considerations
- MO is rare in children younger than 10 years 3
- Atypical locations (such as neck or facial muscles) may present diagnostic challenges and require biopsy to rule out malignancy 4, 6, 7
- Differential diagnosis should include bone and soft tissue malignancies, especially in atypical locations 4
- Recurrence is uncommon after complete resolution 6