[Myositis ossificans circumscripta and sequelae of muscular ischemia. 2 cases]

Non-traumatic myositis ossificans circumscripta is a relatively rare, well defined entity. The pathogenic role of ischemia in its development is discussed.

We report two cases of myositis ossificans circumscripta that occurred in the hamstring muscle respectively 22 and 35 years after ischemic muscular injury in the same site. Clinical and radiologic informations and follow-up were reexamined, showing that patients are usually young and that the disease is equally distributed between both genders. Though the lesion may develop in various muscle, it is preferentially observed in proximal sites. Most patients have a history of localized pain or tenderness accompanied by swelling of the affected site. Following a 5- to 12-week increase, the soft-tissue mass is less sensitive and better defined. It may also resolve in less than 3 years.

Results of X rays, computerized tomography, MR imaging and biopsy are reviewed. Histologically, this lesion main feature is peripheral bone maturation within three areas. Mechanisms (traumatic or not) underlying these lesions are unknown. To our knowledge, only one published case would be comparable to ours. Proliferation followed by change in mesenchymal cells leading to heterotopic ossification must be regarded as a consequence of either ischemia or repeated micro-trauma occurring during muscle shortening.