Eighteen years ago, I had both hips replaced with ceramic implants. They have held up very well for me. I've kept my weight down all these years. But now I'm starting to gain more weight. Will this hurt my hips?

Zirconia ceramic replaced the alumina implants used back in the late 1980s. The ceramic implants had excellent mechanical properties and performed well. They were especially favored because if a crack formed, the material expanded and sealed itself.

Researchers have found that over time, the surface layer of zirconia can change. Contact with water or body fluids increases the grains on the implant surface.

This change decreases the stability of the material making it more likely to wear unevenly. Surface roughness increases. At the same time, crack formation or fracture is more likely.

A recent study of failed and removed zirconia ceramic femoral heads was done. The surgeons found that time was the greatest factor in implant aging. The longer the implant was in place, the more likely the surface layer would undergo changes in stability and wear.

There was no evidence that the patient's age or weight were factors. Activity level was not linked to wear pattern either. Although these factors do not appear to affect zirconia ceramic implants, many other health benefits occur from weight loss and activity. Experts agree that keeping your weight under control and staying active is a recipe for improved overall health.