Heterotopic Ossification

By | 2018-05-30T10:48:16+00:00 June 1st, 2018|
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Bob VogelQ. I’m 34 and in my 10th year as a T6 complete paraplegic. About a year ago, I developed a pressure sore on my sacrum, and a couple months into the healing process I noticed my right hip was red and swollen. My doc put me through a bunch of tests, including a bone scan that confirmed I had heterotopic ossification — bone growth in the tissues around my hip. It has grown so much that it is affecting the range of motion in my hip.

I was prescribed a medication called Didronel to stop the growth. My physician said we can discuss surgery to remove the bone growth to try and regain some range of motion, but not until another bone scan shows it has stopped growing. He also said it is a messy surgery.


What causes heterotopic ossification? What are the signs and symptoms? In addition to medication for stopping growth, is there any way to shrink it? How hard is it to remove?

— Scott

A. Heterotopic ossification is a condition where bone grows in muscle, tendons or other soft tissues around joints in the body. The new bone grows three times faster than normal and can cause jagged, painful joints. In some cases, there is so much growth that it restricts joint movement. HO can also develop into areas that protrude and are prone to cause skin breakdown. In nondisabled people HO is caused by some type of trauma, such as dislocation of the hip or tears in a joint — the body “thinks” the trauma is a fracture and tries to heal it by making bone.

HO in people with spinal cord injury is called neurogenic HO, and the cause in acute SCI is not known. There is no way of predicting who will develop it, says Dr. Douglas Garland, a retired orthopedic surgeon and former director of neurotrauma at Rancho Los Amigos Rehab Center, who has written peer-reviewed papers on the subject. When HO occurs in the acute stage of SCI, it most frequently happens within two months of injury. It can also occur years or decades later and manifests in 10 to 20 percent of people with SCI. It occurs below the level of injury, most frequently in the hip (70 percent) and at the knee (20 percent), but also can occur in the elbow or shoulder. Those with complete injuries are more likely to develop HO than those with incomplete injuries, and HO almost never occurs in people who do not have spasticity.

When HO develops in chronic rather than acute SCI, there is an underlying cause such as a fracture, a bad pressure ulcer or surgery for a pressure ulcer, says Kathleen Dunn, a recently retired clinical nurse specialist and rehab case manager. “Those who had it in the past may find it reactivated by such events years later.” Garland adds that even repeated urinary tract infections can cause HO because UTIs send bacteria throughout the body and can seed the hip with bacteria, causing an infection and HO. “The first thing I think about with new onset HO in chronic SCI is some type of infection,” he says.

The most common symptom for HO is loss of range of motion, explains Dunn. Other signs include one or more of the following: swelling, redness, skin that is warm to the touch around the affected joint, a fever that may increase at night, increased spasticity, pain — if you have sensation in the affected area — and autonomic dysreflexia. “If you are years out from your SCI and suddenly your hip or knee seems warm or swollen, or stiff, or you have other symptoms, you need to address it with your physician right away,” says Garland.

Diagnosis of HO starts with ruling out blood clots, a septic joint or osteomyelitis, as well as cellulitis and other forms of infection, says Garland. At the hip, the most common cause of HO is an infection. At the knee, it is usually caused by fracture — often micro-fracture — that went undiagnosed because lower leg bones become so thin from osteoporosis, it can be difficult to see on an X-ray. When everything is ruled out, diagnosing HO is done with a bone scan — a specialized type of X-ray that involves injecting a radioactive tracer into your body that will “light up” any HO, micro-fracture, or osteomyelitis. HO doesn’t show up on an X-ray until it has progressed.

If HO is diagnosed, the progression can be slowed or stopped by taking non-steroidal anti-inflammatory drugs like Motrin or Celebrex, or a class of bisphosphonates — etidronate disodium, or Didronel — all options to discuss with your doctor. “If you are prescribed these medications, it is important to keep taking them until your physician says it is OK to stop, or HO can return with a vengeance,” says Dunn.
Both Garland and Dunn say that moving the joint can help preserve range of motion. Many information sites on HO list radiation treatment as a way to stop HO from growing, something Garland cautions against. “I don’t think it is a good idea to be irradiating your average person with SCI in their 20s or 30s because it affects the cells decades down the road and can cause cancer. As soon as agents like Didronel came along, I stopped doing radiation treatments on HO.”

The typical case of HO in a person with SCI runs its course in six months, says Garland. Ask for a follow-up bone scan to check that the area of HO no longer lights up.

Unfortunately, although medications can slow or stop the progression of HO, nothing can be done to shrink or reduce it except to surgically remove the HO, usually only if it is seriously interfering with range of motion, which is not to be taken lightly. It is important to find a surgeon with lots of experience with HO. “Even with a skilled surgeon, it can cause lots of blood loss and has the potential for lots of complications, like infection afterward, so it really should be a last resort,” says Dunn. Garland emphasizes the importance of discussing with your doctor the expected surgical outcome and potential complications, and whether the surgery is worth it.

Prior to surgery, it’s important to have a bone scan to check that HO has completely run its course and isn’t growing anymore. If a surgeon cuts out HO before it stops growing, it will grow right back. In order to remove HO, the surgeon does a wedge resection to cut it out. The surgery is followed up with an appropriate NSAID or Didronel to stop the HO from returning following the trauma of surgery.

A caveat about surgery in acute SCI: a small percentage of HO cases — around 10 percent — fall under a different variant, known as Type II. Such cases are so rare that most physicians outside of major rehab centers are not aware Type II exists, according to Garland. The primary way to identify Type II HO is lack of response to treatment. Repeat bone scans will show the HO as “hot” well after six months — because Type II HO is very aggressive and continues to grow for quite some time. Identifying Type II is important because of its tendency to grow back following surgery. Once again, check to make certain a bone scan shows the HO has stopped growing.

For more information on HO, check out the resources below. The Craig module on HO provides a good primer, and SCIRE is an extensive peer reviewed examination of the level of evidence for various treatment options for HO in SCI.

Resources
• Craig hospital education module on heterotopic ossification, craighospital.org/resources/heterotopic-ossification
• SCIRE Heterotopic Ossification Following Spinal Cord Injury, scireproject.com/wp-content/uploads/heterotopic_ossification-version-6.0.pdf