| |
 |
|
| Medical Edge |
|
|
|
Medical Edge Newspaper Column from Mayo Clinic
MONITORING NECESSARY, BUT ARTIFICIAL KNEES COULD LAST ‘FOREVER’
DEAR MAYO CLINIC: My right knee was replaced a year ago, but an X-ray taken this year showed some minor cement-bone irregularities (“radiolucencies”) in the area around the new knee. Are these radiolucencies a sign of future complications? Will the cement get loose and give me joint problems? How long can I expect the new joint to last?
ANSWER: To secure the prosthetic knee in place, surgeons use a superglue-potency cement that melds the new joint to adjacent bone tissue. If the cementing technique were flawless, an X-ray exam performed afterward would show no radiolucency lines — indicators of thin gaps between the bone and the implanted prosthesis. But almost always, minor irregularities occur in the cementing process. The resulting small flaws tend to be inconsequential — as long as they stay small.
When radiolucency lines become wider or longer — usually because of the gradual erosion of bone adjacent to the implanted prosthetic joint — the joint is loosening or shifting. The longer such damage occurs, the greater the amount of bone loss and the more difficult to correct the problem later.
It’s very important to have your prosthetic knee re-examined at regular intervals — typically, every one to two years — because a series of X-rays over time enables the tracking of changes, should they occur. This advisory applies to all knee-replacement patients, regardless of their age or history. It’s actually the younger, fitter and more physically active patients who have the greatest need to monitor their artificial knees. These individuals are more likely to subject their new joints to heavier and more frequent loads.
When bone tissue significantly erodes, the cause is usually microscopic particles that flake away over time from the artificial joint’s plastic layer, which acts like cartilage to create smooth interactions between the joint’s moving components. The amount of such material lost over time is negligible, but the problem is the biological reaction it causes. Because the immune system sees these particles as foreign invaders, it generates chemicals to attack them. A side effect of that process is osteolysis — dissolving of bone tissue — which can affect the bone surrounding and adjacent to the implant.
In affected patients, bones abutting the prosthetic can look as if termites have been eating away at them. Fortunately, though, the process generally is slow and doesn’t advance very far. Its progress varies with the individual: Some patients are highly vulnerable, for example, and others seem not to react at all.
While some of the discussion above may sound grim, incurring such problems within the first few years after surgery is much more the exception than the rule. According to the American Academy of Orthopaedic Surgeons, “The chance of a knee replacement lasting 15 to 20 years is about 95 percent.”
From my own experience as a surgeon, I would say that the statistics, depending on age, health and activity levels, are even better. I like to tell my patients that for most people, a new knee will essentially last “forever” — keeping in mind that the average age of the artificial-knee recipient is about 70.
— Gavan P. Duffy, M.D., Orthopedic Surgery, Mayo Clinic, Jacksonville, Fla.
Additional Resources:
Prosthetic knees
Appointment Information
More Information on Prosthetic Knees
- - -
Medical Edge from Mayo Clinic is an educational resource and doesn’t
replace regular medical care. To e-mail a question, go to www.mayoclinic.org,
or write: Medical Edge from Mayo Clinic, c/o TMS, 2225 Kenmore Ave.,
Suite 114, Buffalo, N.Y., 14207. For health information, visit www.mayoclinic.com.
© 2006 TRIBUNE MEDIA SERVICES, INC.
|
|
