For many people who have suffered from an arthritic hip, the replacement of their natural hip bone with a prosthetic implant has meant an end to constant pain, and the restoration of a normal range of movement. Unfortunately, the ball-and-socket joints of the prostheses do wear down over time, so younger patients in need of the implants are typically told to either wait until they are older, or must face the prospect of someday requiring repeat surgery to service their device. A recent discovery, however, could lead to longer-lasting artificial hip joints - this could in turn allow patients to receive prosthetic hips at a younger age, without the need for additional surgery when they get older.

Although a previous generation of artificial hips used a combination of metal and polyethylene surfaces for their ball-and-socket joints, these have since largely been replaced with longer-lasting metal-on-metal joints. It had previously been observed that over time, a lubricating layer formed between the two metal surfaces, once the implant had been in use in the body. Scientists generally assumed that this layer was made from some sort of protein from the body, as is the case with natural skeletal joints.

Recently, however, a team of physicians and engineers from the United States and Germany analyzed the lubricating layer on metal joint components that had been removed from patients in revision surgeries. To their surprise, they discovered that the layer was composed at least partly of graphite carbon. This is a solid lubricant, which is typically used in industrial applications.

"Knowing that the structure is 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," said team member Dr. Alfons Fischer, of Germany's University of Duisburg-Essen. "We now have a target for how we can improve the performance of these devices."

The researchers now plan on correlating the condition of layers on removed implants with those implants' reasons for removal. They are also studying how neighboring cells could be affected by graphite particles that flake off of artificial hip joints.

The study was funded by the National Institute of Arthritis and Musculoskeletal and Skin Diseases. A paper on the research was published on December 23rd in the journal Science.