Circumscribed myositis ossificans. Report of nine cases without history of injury.

The clinical features of 9 patients with circumscribed myositis ossificans (CMO) are described and the effects of treatment with surgical removal of ectopic bone are assessed. The average age of these patients was 24.4 years, and the average follow-up period was 7.4 years. Early correct diagnosis remains unusual, mainly because myositis may be mistaken for bruising, sarcoma or mumps. Once histological diagnosis was established in biopsy, surgical resection of the mass was found in these series. Although spontaneous recurrence was found in this series. Although spontaneous regression of the clinical findings has been reported, we consider surgery to be necessary in CMO in order to establish the diagnosis; furthermore, when the clinical and radiological diagnosis is uncertain or when the lesion causes pain or mechanical blocking of a joint, the removal of the mass is mandatory.