On September 17, 2007, New Jersey Governor Jon Corzine underwent a single radiation treatment to his hip area the morning of his hip replacement surgery. The purpose was to prevent the recurrence of a medical problem he incurred, after his shattered hip and thighbone were operated on after an automobile accident he sustained last April.
The condition is called heterotopic ossification (hereafter referred to as HO). The role of radiation therapy for this non-malignant medical problem is relatively unknown by most people but is quite useful.
Background
HO is the formation of rigid bone in places it doesn't belong, namely in the flexible muscles that surround the hip joint. It occurs as a complication of total hip replacements, anywhere from 8-90% of the time, with an average occurrence rate of 40%.
HO can be identified on x-rays of the hip as early as three to six weeks after the operation. However, its effects, such as hip pain and impaired joint mobility limiting the person from climbing stairs, bending forward to tie his or her shoe laces, and arise out of a chair, usually take six to twelve months to develop. The only effective treatment for HO is re-operation, as in the case of Governor Corzine. Needless to say, it is desirable to avoid such a complication.
Who is at Risk?
Risk factors for HO include: male gender, people over age 60, history of severe osteoarthritis, arthritis of the hip following hip trauma, previous surgery on the same hip, and prior HO in the opposite hip.
How does HO occur?
Although the mechanism is not clear, one theory is: in the setting of hip trauma or surgery, bone fragments shed into the surrounding muscle tissue. There, immature connective tissue cells mature into bone cells, which then multiply and form bone in the muscle.
How radiation therapy works
Radiation therapy interferes with the production of DNA by the aforementioned immature connective tissue cells. Thus, the cells cannot multiply and give rise to bone tissue where it does not belong.
History of radiation therapy to prevent or decrease the risk of HO
Radiation therapy was first used to prevent or decrease the risk of HO in the 1970s. With the emergence of new technology, radiation therapy techniques have evolved over the decades.
For example, in the past, radiation therapy was delivered over a series of several treatments administered over the course of one to two weeks. Today, it is usually administered in a single dose.
In addition, as the prosthesis (artificial hip joint) used in total hip replacement surgery has also improved over the decades, so the area of the hip that needs to be treated with radiation therapy after the operation has gotten smaller.
Timing of radiation therapy
It is known that radiation therapy is effective when it is delivered to prevent HO. This is called prophylactic radiation therapy. Radiation therapy is not beneficial once HO has ensued. Therefore, radiation therapy needs to be administered either within 96 hours after the surgery or within four hours prior to surgery.
Radiation therapy for joints other than the hip
Prophylactic radiation therapy is also used for other joints, such as the elbow, wrist, shoulder and TMJ (the hinge joint of the jaw).
Outcomes
The incidence of HO decreases from an average of 40% in people who do not undergo radiation therapy, to 5% for those who do. This translates into a significant benefit.
Complications
Theoretically, radiation therapy can cause cancer. However, to the present, no such complication has been documented in the medical literature.
Also, because the area that is exposed to radiation therapy is near the reproductive organs, fertile people need to practice birth control for one year. This is because radiation has the potential to cause genetic damage in sperm and eggs.
In reality, there are usually no adverse side effects from radiation therapy to treat HO.
Conclusions
Radiation therapy is a useful and safe treatment to prevent heterotopic ossification in people who undergo hip replacement surgery. For more information about radiation therapy, visit http://www.rtanswers.org
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