An HSS study provides the first comprehensive look at why some metal-on-metal total hip replacements fail in patients. In the study, presented at the 2012 Annual Meeting of the American Academy of Orthopaedic Surgeons, scientists analyzed 46 failed metal-on-metal hip replacements. Made possible by the largest archive of failed implants in the country, the research should help doctors develop a better hip replacement prosthesis for future patients.
The most common diagnoses were wear-related concerns such as dissolving bone and adverse soft tissue reactions. Ninety-eight percent of the implant cups and 93 percent of the heads showed moderate to severe scratching. Forty-three percent of the cups and 67 percent of the heads had moderate to severe pitting.
“This paper is the first step towards understanding what the problems are with metal-on-metal joints. Information gleaned from the study should be useful as well in improving metal-polyethylene implants, the most common hip implant today,” said co-author Timothy Wright, PhD, F.M. Kirby Chair of Orthopaedic Biomechanics. “The study suggests that the physical design of the implant might play a role in the failed metal-on-metal implants and not the metal itself.”
In recent years, advances in materials have allowed implants with bigger heads to be used, which increases stability, but now evidence suggests this may cause other problems. “What we learn about the effect of head size and positioning, and what we learn about the biologic reaction to metallic debris, is going to help us understand problems in general with joint replacements,” says coauthor Douglas Padgett, MD, chief of the Adult Reconstruction and Joint Replacement Division at HSS.
“A follow-up analysis using high resolution laser profiling to quantify damage is in process.” Findings will help doctors and scientists improve implant design.
Read the full Discovery to Recovery Fall 2012 issue.