Myositis ossificans

X-ray shows evidence of periosteal reaction along the medial aspect of lower end of right femur with a relatively radiolucent central area and radiodense periphery and displacement of fat planes in the adjacent soft tissue suggestive of heterotropic bone formation. Diagnosis is myositis ossificans.

Non-traumatic myositis ossificans is benign heterotropic ossification characterized by the aberrant formation of bone in extraskeletal soft tissues.¹ It is usually confined to a single muscle or muscle group, most commonly in quadriceps, gluteals, small muscles of hand and brachialis. It is most common in active male within the second and third decade of life. It usually occurs after muscle injury such as repeated microtrauma, but it can also occur without previous trauma in patients with burns, neuromuscular disorders, hemophilia, tetanus, and drug abuse.^2,3 Myositis ossificans is essentially a proliferative mesenchymal response to an initiating injury to the soft tissue, not necessarily to the muscle, which leads to localized ossification. The mechanism suggested is the abnormal differentiation of fibroblast to bone forming cells under the influence of bone morphogenic protein 2.⁴ Myositis ossificans is a self limiting condition resolving in about 6 months. It needs to be differentiated from osteosarcoma. In the acute phase which lasts for upto 3 weeks they should be managed conservatively with compressive dressing, avoidance of additional injury and physiotherapy. The resolution of the lesion correlates with decreasing alkaline phosphate values. The lesion shouldn't be removed surgically until the lesions have matured as there is high risk of recurrence.