In a new study, physicians and engineers from the US and Germany suggest that the lubricant found in metal-on-metal hip implants is graphite, which reportedly parallels the lubrication of a combustion engine more so than that of a natural joint. The National Institute of Arthritis and Muscoskeletal and Skin Disease (NIAMS), a part of the National Institutes of Health (NIH), funded the study. 

NIAMS director Stephen I. Katz, MD, PhD, explains that, "The results of such research could have important implications for several hundred thousand Americans who undergo hip replacement each year, as well as those who could benefit from the procedure but have been advised by their doctors to delay surgery until they are older."

Joshua Jacobs, MD, study lead investigator, and chair of the department of orthopaedic surgery at Rush University Medical Center, Chicago, Ill, echoes and expounds upon Katz’s statement. While hip replacement surgery can provide pain relief and a return to normal life, "For younger, more active people, the prostheses’ limited longevity often means postponing surgery, often for a number of years, or having the surgery and facing the prospect of a more difficult repeat surgery at some point when the prosthesis fails," this, Jacobs emphasizes, is why researchers have searched for ways to improve the materials currently used. He points to metal-on-metal systems, indicating that the devices have tended to release more metal debris through wear and corrosion than devices that have performed well. 

Researchers report that in order to form a clearer picture of what occurs in artificial joints and what can be improved, they analyzed metal joint components removed in revision surgeries and focused on friction, lubrication, and wear. 

While prior studies suggested that a lubricating layer forms on metallic joints as a result of friction, the new study reportedly indicated a different cause behind the formation of the layer. According to researchers, the layer consists in large part of graphitic carbon, a solid lubricant with industrial applications. 

"Knowing that the structure is a graphitic carbon really opens up the possibility that we may be able to manipulate the system in such a way as to produce graphitic surfaces. We now have a target for how we can improve the performance of these devices," study researcher Alfons Fischer, PhD, professor of science and engineering at the University of Duisburg-Essen, Germany, adds.

Further research, the team says, will evaluate surfaces of retrieved devices and correlate observations with the reason for removal.

Source: NIH