23/06/2026
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Myositis ossificans is a benign form of heterotopic ossification characterized by the formation of mature bone within skeletal muscle or soft tissues, most commonly following trauma. It is considered a "don't touch" lesion because its appearance may mimic malignant tumors, particularly during the early stages of development.
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Myositis ossificans results from metaplastic bone formation within injured soft tissues. Following trauma, fibroblasts within the connective tissue differentiate into osteoblasts, leading to the production of osteoid and subsequent bone formation.
The lesion matures through a characteristic zonal pattern:
- Peripheral zone: Mature lamellar bone.
- Intermediate zone: Osteoid and immature bone.
- Central zone: Fibroblastic tissue without ossification.
This maturation occurs from the periphery toward the center, a feature that helps distinguish myositis ossificans from malignant bone-forming tumors.
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๐ทEarly Stage (0โ2 Weeks)
- Soft tissue swelling may be present.
- No visible calcification.
- Radiographs may appear normal.
๐ทIntermediate Stage (2โ6 Weeks)
- Peripheral calcification begins to develop.
- Patchy mineralization within the soft tissue mass.
๐ทMature Stage (6โ8 Weeks and Beyond)
- Well-circumscribed lesion with dense peripheral ossification.
- Central radiolucent area.
- Characteristic zonal pattern with peripheral maturation.
- A radiolucent cleft (String Sign) may separate the lesion from the adjacent cortex.
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The hallmark feature of myositis ossificans is peripheral predominant ossification with a relatively lucent center, reflecting maturation from the outside inward. This finding helps differentiate it from parosteal osteosarcoma, which typically demonstrates central ossification adjacent to the cortex.This format is suitable for radiography notes, assignments, and exam preparation.
