Joint replacement material developed at the MGH

On July 16, MGH surgeons performed the first total hip replacement using a joint socket lined with a novel material invented at the MGH. An advance over first-generation highly crosslinked polyethylene — which was also developed at the MGH and significantly reduced a serious complication of early hip implants — the new material may be applied in replacements for a wider variety of joints in a more diverse group of patients.

“We think this material could be used for any joint in the body and in any implant design, even those demanding higher flexion and more mobility,” says Orhun Muratoglu, PhD, co-director of the Harris Orthopædics Biomechanics and Biomaterials Laboratory (OBBL) at the MGH. Muratoglu developed the new material in collaboration with scientists at the Cambridge Polymer Group.

Soon after total replacements for hips and other joints were developed in the late 1960s, it became apparent that hip implants could loosen and eventually fail. A team led by William Harris, MD, DSc, now director emeritus of the MGH OBBL, found that long-term friction of the implant’s head against the polyethylene-lined joint socket would break off small particles of polyethylene. The body’s immune system reacted against these foreign particles, eventually destroying adjacent bone tissue and loosening the implant.

Harris and his colleagues found that high doses of radiation would “crosslink” the polyethylene, bonding molecules together to produce a much more durable material, and melting the material could eliminate free radicals generated by the radiation. The first-generation highly crosslinked polyethylene was approved by the FDA for use in implants in 1999; but it had limitations in strength that made it unsuitable for some types of joint replacement implants. Subsequently, Muratoglu found that diffusing the antioxidant vitamin E throughout the polyethylene would also block oxidation and produce a much stronger material. Vitamin-E-stabilized, highly crosslinked polyethylene has received FDA approval for use in joint implants and is being further tested in an international clinical trial.

“This material will allow us to offer our patients long-term, high-performance joint replacements,” says Andrew A. Freiberg, MD, chief of the Arthoplasty Service in the MGH Department of Orthopædics, who performed the first replacement using the material. “It should be suitable for higher-stress applications in younger patients, those who are more active and those who are heavier.”