Infusing antioxidants into the plastic surface between metal components of total joint replacements may help the implants last longer and reduce damage to surrounding bone. A group of researchers in the Center for Musculoskeletal Research at the University of Rochester Medical Center showed that an antioxidant, called COVERNOX™, promotes both destruction and rebuilding of bone in a mouse model, but favors rebuilding.
About 7 million people are currently living with a hip or knee replacement in the US, which is a common last resort for end-stage joint disease. Many adults with severe osteoarthritis in their 50’s or 60’s are undergoing total joint replacement surgery, meaning that implants may need to last 30 or 40 years. However, twenty percent of patients experience implant failure within 10 years of their original surgery.
“Joint replacement surgery is largely regarded as the most successful medical procedure of the 20th century, but implants are not permanent,” says Edward Schwarz, PhD, director and Richard and Margaret Burton Distinguished Professor of Orthopaedics in the Center for Musculoskeletal Research at the University of Rochester Medical Center. “They wear out like tires on a car.”
Implant failure is caused by erosion of the implant surfaces over the years, which releases particles and reactive oxygen species into the joint. Those particles cause inflammation that sends the normal cycle of bone destruction and rebuilding out of kilter – favoring destruction. This leads to loosening of the implant, which often requires an invasive revision surgery to replace it.
Schwarz and Chao Xie, BMed, assistant professor of Orthopaedics at URMC demonstrated that COVERNOX™ antioxidant could help tip the bone destruction-to-rebuilding balance toward rebuilding. The group infused the antioxidant into plastic that is commonly used to coat metal joint replacement implants and tested its effect in mice. The COVERNOX™-infused particles resulted in a net gain of new bone, whereas the non-infused particles showed no net gain or loss.
In the study, which was featured on the cover of this month’s Journal of Orthopaedic Research, the authors acknowledge that the mouse model they used was imperfect. They tested COVERNOX™ on smooth bone rather than an articulated joint. Despite this caveat, Schwarz believes that their results are applicable to human joints because, “we’re looking at a cellular/molecular level and that’s exactly the same between humans and other animals.”
This will soon be tested in forthcoming clinical trials by DePuy Synthes, the Johnson & Johnson company that developed COVERNOX™. Those trials, which are currently awaiting approval from the Food and Drug Administration, were informed by Schwarz’s team’s research on the optimal amount of COVERNOX™ to infuse into the plastic coating of bone implants.
To read the full study, click here.