Abnormal bone growth. X-ray of the hip joint of a 60-year-old man suffering from the bone and muscle disorder myositis ossificans or heterotopic ossification. There is an extraneous growth of bone where the surrounding muscle and tissue has ossified (turned into bone). Part of this overgrowth (lower centre) is seen protruding from the normal upper leg bone (femur). The condition is normally a result of trauma to the affected area. The growth calcifies from the outside in, in contrast with an osteosarcoma (another type of bone growth), which calcifies from the inside out. Surgical excision is an option when bone activity stops. If left alone, the growth should shrink.