Heterotopic ossification is a synonym for myositis ossificans. Myositis ossificans(MO) is a benign, extra-osseous area of active bone formation. It often follows trauma but the trauma may not be severe and may not be associated with an obvious hematoma. During the period of active calcification, the bone scan is nearly always 4+ intense. After several months(12-24 in our experience) the intensity of the bone scan decreases. If surgical therapy is considered, it is usually delayed until the bone scan intensity subsides in order to minimize the chances of recurring bone formation. Calcification also may spontaneously subside with time.
Several theories exist as to the cause of MO. It may be the result of a hematoma, or may be due to a disrupted periosteum that has been pushed into muscle tissue. Pleuri-potential soft tissue stem cells also seem to play a role in the bone formation.