Heterotopic ossification (HO) is the process by which bone tissue forms outside of the skeleton.

Contents 1 Diagnosis 2 Causes 3 Symptoms 4 Treatment 5 See also 6 References 7 External links

[edit] Diagnosis

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 also not very helpful; alkaline phosphatase will be elevated at some time, but in patients who have had fractures or spine fusion recently, this is not diagnostic. The values will often be quite high but unless weekly tests are done this peak value may not be detected. Initially the value may be only slightly elevated. The only definitive diagnostic test in the early acute stage is a bone scan. When the initial symptoms are an acute inflammatory process with swelling and increased temperature, the differential diagnosis is thrombophlebitis. It may be necessary to do a bone scan and a venogram to differentiate which is present, and it is even possible that both could be present simultaneously. The swelling tends to be more proximal with little or no foot/ankle edema; whereas, in thrombophlebitis the swelling is more uniform throughout the leg. ^[1]

[edit] Causes

Study on heterotopic ossification has suggested that it may be linked to injuries to the spinal cord, along with neurological conditions. It appears that mixed signals in the body stimulate normally dormant osteoprogenitor cells, causing them to start growing bone. When these cells are in the soft tissues of the body, it results in heterotopic ossification. The condition often appears in the form of periarticular ossification, especially around the site of hip injuries. ^[2]

[edit] Symptoms

In addition, the bone scan will show heterotopic ossification seven to ten days earlier than an x-ray. The three-phase bone scan is perhaps the earliest method of detecting heterotopic bone formation. However, in some cases, an abnormality may be detected in the early phase which does not necessarily mean it will go on to form heterotopic bone. Another finding, often misinterpreted as early heterotopic bone formation, is an increased (early) uptake around the knees or the ankles in an early spinal cord injured patient. 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. ^[3]

[edit] Treatment

The effect of Didronel is to prevent calcium from being deposited in the bony matrix that has already been formed. Therefore, it is essential to make the diagnosis as soon as possible (preferably before any calcium shows up on x-ray) and start the Didronel immediately. Didronel will do nothing to remove calcium that has already been deposited. It is a preventative drug, and has no effect on existing ossification. It also has no effect on the underlying process which produces the bony matrix. There are no known side effects that would prohibit usage. Many physicians recommend prophylactic use of Didronel in all acute spinal cord injuries, but because of the cost this may not be practical. Some patients complain of nausea the first week, but this is rarely severe enough to stop treatment and usually subsides in a few days. There is no uniform agreement on how long Didronel should be continued. In most cases, there will be a brief flare-up of the heterotopic ossification following discontinuation of Didronel, and some cases an increase in the amount of calcium deposited. There are no completely reliable tests to indicate that the heterotopic ossification is inactive and treatment can be safely stopped. However, if the treatment is continued long enough this additional calcium deposition will be of minimal clinical significance. The patient needs to be observed closely for signs of recurrence whenever treatment is discontinued. ^[4]

[edit] See also

• Myositis ossificans
• Fibrodysplasia_ossificans_progressiva

[edit] References

[edit] External links

• Duke Orthopedics heterotopic_ossification
• pmr/112 at eMedicine
• radio/336 at eMedicine
• New study finds way to stop excessive bone growth