Heterotopic ossification, or the periarticular formation of bone, occurs frequently as a secondary complication of severe spinal cord trauma, head trauma, burn, total joint arthroplasty and other neurologic injuries. The etiology is still unknown. It's clinical manifestations are pain, swelling, limitation in range of motion and progressive deterioration in function, soon thereafter. Because of the late detection of this lesion there is some delay when to start medication, or when to do physical therapy. The purpose of this study is to find out the importance of the early diagnosis and treatment of heterotopic ossification. We analyzed the clinical course of Heterotopic ossification in 21 patients (spinal cord injury: 12, head injury:9) who had admitted to St. Mary's Hospital, Catholic University of Medical College, from January 1985 to June 1989.

The results were as follows:

1) The mean age were 43.1 years. 83.3% of all the spinal cord injured patients were older than 30 years and 75.0% of all the head injured patients were older than 50 years.

2) Male was more affected than female in both case.

3) The common site of heterotopic ossification were hip, knee in spinal cord injury, and knee, shoulder, hip, elbow and ankle in head injury I order.

4) The mean duration from the injury to the onset of clinical manifestation was 17 days. Serum alkaline phosphatase began to rise on 127th day and radiological bone formation could be seen on 214th day post injury.

5) The risk factors related to ectopic bone formation in spinal cord injured patients were spasticity (100%), age over 30 years (83.3%), presence of pressure sore (58.3%) and completeness of lesion (58.3%), while those in head injured patients were spasticity (100%) and type of brain injury (ICH; 50.0%).

Thus serial determinations of the serum alkaline phosphatase and follow-up check of roentgenograms at frequent intervals are prerequisites to early diagnosis and early treatment of ectopic bone formation in high risk patients.