Metal-on-Metal Hip Pain Likely Caused by Tissue Damage: Study

Researchers indicate that individuals who suffer unexplained hip pain after receiving a metal-on-metal hip replacement are likely suffering tissue damage, as opposed to wear or degradation of the components. 

The study was conducted by researchers from the Hospital for Special Surgery (HSS), and was presented at the annual meeting of the American Academy of Orthopaedic Surgeons in Chicago.

Although many suspect that such pain is caused by wear of the hip replacement, researchers determined recipients are usually experiencing tissue damage around their implant.

The study looked at nearly 100 patients with metal-on-metal hip replacement systems, half of whom needed revision surgery. The researchers found that patients with tissue damage around their implants were ten times as likely to have unexplained hip pain.

The study comes amid increasing concerns over the safety of metal-on-metal hip replacements. In recent years, several models have been linked to unusually high failure rates and revision surgeries, with many systems recalled from the market.

There are also concerns about metal debris shed into the body as the metal components rub against each other, which has been linked to the incidents of tissue damage as well as high levels of metal ions in the blood, a form of metal blood poisoning known as metallosis. Researchers say that tissue damage may be what is ultimately causing recipients to experience unexplained pain.

“We found that some patients had a significant amount of tissue damage but not a lot of wear, suggesting that factors other than wear are contributing to the problem regardless of whether the patients have pain,” said Dr. Timothy Wright, Kirby Chair of Orthopedic Biomechanics at HSS. “We have used the information from our study to develop guidelines for patients and surgeons.”

In January, the FDA released new guidance for metal-on-metal hip replacements. The agency told doctors that metal-on-metal hip replacement systems should only be used if other artificial hip implants were not appropriate, and called on manufacturers to prove that their implants were safe enough to stay on the market. Future metal-on-metal hip designs will have to undergo extensive human clinical trials before being made available for sale, the FDA decreed.

DePuy Orthopaedics, a subsidiary of Johnson & Johnson, faces thousands of lawsuits over its recalled DePuy ASR metal hip replacement system. In addition, a growing number of lawsuits have been filed over other metal-on-metal hip systems, including the DePuy Pinnacle hip, Biomet M2A Magnum hip and Wright Medical Conserve Cup.