Within the past decade, the Oxinium knee replacement entered the marketplace.

It uses a kind of metal alloy that transforms to have a ceramic outer surface as oxygen from the body penetrates it. This makes the surface particularly smooth and hard, theoretically reducing joint friction and extending the life of the replacement.

“This is an advance in metallurgy, but we don’t yet know if it will actually translate into any clinical benefit,” says Thomas Ambrose, MD, associate professor of orthopaedic surgery at the Indiana University School of Medicine in Indianapolis.

Most companies making TKR systems have been working on making both the metal smoother and the plastic stronger, and stronger plastic may have an advantage. “When plastic wears, it generates microscopically small particles,” Dr. Ambrose says. “The body sees these as foreign, mounting an inflammatory response to remove the particles.”

Surgeon skills and experience. Don’t focus so much on the implant that you overlook other critical factors.

“The most important thing is not the implant but who is going to put it in,” says Dr. Kraay. “One of the best predictors of success in TKR is the experience of the surgeon, with the number of procedures done in the hospital you select following right behind.”

Dr. Ambrose agrees, noting that research has shown better patient outcomes if the surgeon does at least 50 knee replacement surgeries a year.

“Most TKR surgeries done even 15 years ago are still working today,” he says. “This is long before advances in metallurgy, plastic sciences or even the current understanding of the importance of proper installation. We have gained a lot of knowledge over the years that will probably translate into an even bigger longevity benefit than the bells and whistles.”