Two cases of myositis ossificans in children, after prolonged immobilization.

Myossitis ossificans (MO) is a benign disorder characterized by heterotopic bone formation in skeletal muscle. It is divided in three types, fibrodysplasia ossificans progressive (FOP), myositis ossificans circumscripta or traumatica (MOT) and myositis ossificans without a history of trauma (non traumatic or pseudomalignant MO). Myositis ossificans is extremely rare in children younger than 10 years. We present the clinical and radiological findings of two 5-year-old children with pseudomalignant MO due to prolonged immobilization. Plain x-ray films and CT scan with their characteristic findings of mature bone in the periphery of the lesion with smooth contour and well separated from the bone, enabled us to diagnose the lesion. To the best of our knowledge, no such cases have been reported in the literature.