<P> Another rare genetic disorder causing heterotopic ossification is progressive osseous heteroplasia (POH), is a condition characterized by cutaneous or subcutaneous ossification . </P> <P> In traumatic heterotopic ossification (traumatic myositis ossificans), the patient may complain of a warm, tender, firm swelling in a muscle and decreased range of motion in the joint served by the muscle involved . There is often a history of a blow or other trauma to the area a few weeks to a few months earlier . Patients with traumatic neurological injuries, severe neurologic disorders or severe burns who develop heterotopic ossification experience limitation of motion in the areas affected . </P> <P> During the early stage, an x-ray will not be helpful because there is no calcium in the matrix . (In an acute episode which is not treated, it will be 3--4 weeks after onset before the x-ray is positive .) Early laboratory tests are not very helpful . Alkaline phosphatase will be elevated at some point, but initially may be only slightly elevated, rising later to a high value for a short time . Unless weekly tests are done, this peak value may not be detected . It is not useful in patients who have had fractures or spine fusion recently, as they will cause elevations . </P> <P> The only definitive diagnostic test in the early acute stage is a bone scan, which will show hetertopic ossification 7--10 days earlier than an x-ray . The three - phase bone scan may be the most sensitive method of detecting early heterotopic bone formation . However, an abnormality detected in the early phase may not progress to the formation of heterotopic bone . Another finding, often misinterpreted as early heterotopic bone formation, is an increased (early) uptake around the knees or the ankles in a patient with a very recent spinal cord injury . It is not clear exactly what this means, because these patients do not develop heterotopic bone formation . It has been hypothesized that this may be related to the autonomic nervous system and its control over circulation . </P>

A joint that is eventually replaced by bone