Researchers at Rush University Medical Center (Chicago, IL, USA), the University of Duisburg-Essen (Germany), and Northwestern University (Evanston, IL, USA) studied seven implants that were retrieved from patients for a variety of reasons. The researchers used a number of analytical tools, including electron and optical microscopies, to study the tribological layer that formed on the metal parts. Electron-energy loss spectra--a method of examining how the atoms are bonded--showed a well-known fingerprint of graphitic carbon. This, together with other evidence, led the researchers to conclude that the layer actually consists primarily of graphitic carbon, a well-established solid lubricant, and not proteins secreted by natural joints.

According to the researchers, metal-on-metal implants have added advantages over other types of implants, since they are a lower wear alternative to metal-on-polymer devices and also allow for larger femoral heads, which can reduce the risk of hip dislocation, one of the more common reasons for additional surgery. Metal-on-metal is also is the only current option for a hip resurfacing procedure, a bone-conserving surgical alternative to total hip replacement. Manipulating the implant design to encourage the production of graphitic surfaces could improve and prolong the performance of these implants. The study was published in the December 23, 2011, issue of Science.

“Hip replacement surgery is the greatest advancement in the treatment of end-stage arthritis in the last century,” said study coauthor Professor of orthopedic surgery Joshua Jacobs, MD, chair of the department of orthopedic surgery at Rush. “By the time patients get to me, most of them are disabled; life is unpleasant. They have trouble working, playing with their grandchildren or walking down the street. Our findings will help push the field forward by providing a target to improve the performance of hip replacements. That’s very exciting to me.”

Related Links:
Rush University Medical Center
University of Duisburg-Essen
Northwestern University