Researchers Find Improved Polymer For Application in Hip Joint Reconstruction

Researchers in the Campbell Clinic Department of Orthopaedic Surgery at the University of Tennessee Health Science Center in Memphis, Tennessee, today presented a paper that indicates a new polymer under study for applications in joint reconstruction can significantly reduce up to seven times the harmful chemicals formed as a result of the presence of wear particle debris in the body. This debris is well-known to cause loosening of the hip implants and thereby limit the useful life of these commonly used artificial joints.

The paper, authored by Richard A. Smith, PhD, an assistant professor at UT Health Science Center, was presented today at the combined meeting of the world's Orthopaedic Research Societies in Honolulu, Hawaii. The research was sponsored by Active Implants Corporation (AIC), a developer of pliable implant technology for orthopaedic applications.

A desire to implant artificial joints in younger patients, the prospect of a potential longer life expectancy for hip implant patients, and an increase in demand by patients for greater activity are all driving a search for longer-lasting artificial hips.

One avenue of research is related to the reaction of implant materials to infections. Researchers have widely recognized that one of the first places infections migrate in the body is the joints. Previous research by this group found that even minute infections that do not cause any clinical symptoms, such as those that enter the body during tooth brushing, can become attached to the wear particles of the traditional plastic material used in joint replacement, a special type of polyethylene called UHMWPE, a plastic that articulates or rubs against an artificial hip implant. Over the years, researchers have observed that once attached to the wear particles, infectious agents can create chemicals that destroy the bone around the hip joint by a process called "osteolysis." This bone destruction can lead to implant loosening, which often leads to pain and an implant failure requiring major revision surgery.

Using particles of a special, medical grade form of polyurethane polymer, UT Health Science Center researchers found a significant reduction (up to seven times less) in the production of these harmful chemicals when exposed to infectious agents.

"Our laboratory has been studying the wear particles of the polyethylene material used in artificial joints for many years. This alternative material has produced results that warrant further research to confirm its superiority as a plastic implant material," said Dr. Richard A. Smith, the UT Health Science Center researcher.

"From an orthopaedic surgeon's perspective, I believe these findings are significant, and a signal that we may have entered a new era of joint replacement materials," said Dr. Michael Lewis, executive vice president for Medical Development of AIC.

"The orthopaedic industry has been searching for over 40 years for a replacement of the traditional polyethylene used in hip replacement. Many have viewed this material as the weakest link in today's total joint reconstructions. This groundbreaking research demonstrates we may have found not only a replacement, but an improved material," said Robert Rylee, past president of Wright Medical Company and board member of Active Implants.

"This research, combined with other studies, confirms this family of polyurethane materials, used for years in cardiovascular applications, has properties equal to and now better than the traditional polyethylene used for joint replacement," said Stephen Bradshaw president and chief executive officer of Active Implants Corporation. "AIC is a pioneer of advanced pliable structured material applications in orthopaedics and is pleased to contribute to the progress of a technology that will benefit patients around the world."

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