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Fact Sheet 1: Heterotopic Ossification in Spinal Cord Injury


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Guidelines for Management:

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: The onset can occur in three ways:

  1. Sudden acute onset with an acute inflammatory process characterized by swelling, pain (if the patient has enough sensation to perceive the pain) and local increased temperature which is frequently mistakenly diagnosed as thrombophlebitis.
  2. Begins insidiously with no obvious inflammatory signs. The first evidence of its presence is usually discovered by an astute physical therapist who notes decreasing range of motion in a joint despite daily range of motion exercises. Any time this occurs it should be assumed to be due to heterotopic ossification until proven otherwise.
  3. Knee effusion - The sudden occurrence of knee effusion with no history of trauma should always raise a suspicion of HO - which may be located in the hips or thigh quite remote from the knee.

Differential Diagnosis:

  1. X-Ray: 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.)
  2. Laboratory Tests: 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.
  3. Bone Scan: 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.
  4. Clinical Exam: 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.

    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.

Management:

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.

  1. Vigorous physical therapy to maintain as much range of motion in the joint as possible, keeping in mind the risk of fracture due to osteoporosis.
  2. Didronel, at a dosage of 20 mg/kg body weight for 14 days, then reduced to 10 mg/kg body weight for a minimum of 3 to 6 months in a confirmed case 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.

Duration of Treatment:

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.


References:
"Heterotopic Ossification After Spinal Cord Injury," Samuel L. Stover, MD, Chapter 11 in Management of Spinal Cord Injuries, edited by R. F. Bloch, MD, PhD; M. Basbaum, MSW and Wilkins, 1986, pp 284-301.


Developed by: Shirley McCluer, M.D., Medical Director, Arkansas Spinal Cord Commission.
Date: December 1990. Published by the Arkansas Spinal Cord Commission, 1501 North University, Suite 470, Little Rock, AR 72207. Phone: (501) 296-1788 (voice) / 296-1794 (tdd)