Heterotopic ossification (HO) is a fairly common complication in spinal cord injury. It can range anywhere from a small amount of bone noted as an incidental finding on an X-ray to massive bone formation around a joint resulting in total ankylosis. It occurs only below the level of injury. The most common location is in the hips. Other locations in descending order of frequency: knees, shoulders, and elbows. It does not occur below the knees or below the elbows. Upper extremity involvement occurs only in quadriplegics. It can occur in either complete or incomplete injuries, with either traumatic or non-traumatic etiology. The most common time of onset is between one and four months after onset of the spinal cord injury. However, subsequent events, such as decubitus ulcers or fractures, can also stimulate the process. The etiology is unknown and there is no way to predict which patients are more likely to develop heterotopic ossification or which patients are likely to have only a mild form.
Recognition:
On palpation, the swelling seems to be firmer and more localized than with thrombophlebitis. However, it must be kept in mind that it is not possible to make an absolute diagnosis on clinical examination alone - one can only have a high degree of suspicion.
The most serious consequenceof heterotopic ossification is permanent loss of range of motion in the affected joint. The potential for this depends on location of the ossification, whether it occurs around a joint or along the shaft of a long bone, and on the amount of bone deposited. Therefore, treatment is directed toward prevention of this loss of motion.
There are two essential factors in treatment of heterotopic ossification.
In order to get effective drug absorption, it is very important for the tablets to be given all at one time (once daily) on an empty stomach and no food taken for at least 2 hours afterward. Therefore, the usual administration time is 2 hours before breakfast. Juice may be used to help swallow the tablets.
The effect of the Didronel is to prevent calcium from being deposited in the bony matrix that has already been formed. Therefore, it is essenial 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 the Didronel should be continued. In most cases, there will be a brief flare-up of the heterotopic ossification following discontinuing the Didronel and some 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 was continued long enough this calcium deposition will be of minimal clinical significance. The patient needs to be observed closely for signs of recurrence whenever treatment is discontinued.
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