Unicameral bone cysts. Natural history and the risk of fracture.

Unicameral bone cysts in 57 patients, seen at the Alfred I. duPont Institute between 1949 and 1982, were studied retrospectively. We present the natural history in several patients and report a "cyst index" which allows the progress of the cyst to be followed and makes it possible to determine whether there is a significant risk of fracture which would warrant treatment. We have found that measuring the cyst index in patients treated by injections of methylprednisolone acetate helps to assess the response to treatment.