New Joint Replacement Material Put to First Clinical Use
New form of polyethylene will allow stronger, more versatile joint replacement
Massachusetts General Hospital (MGH) surgeons have performed the first total hip replacement using a joint socket lined with a novel material invented at the MGH. “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 MGH, who developed the new material in collaboration with scientists at the Cambridge Polymer Group.
Total replacements for hips and other joints were developed in the late 1960s, but it soon became apparent that hip implants could start loosening about 5 years after surgery and would eventually fail completely. A team led by William Harris, MD, DSc, director emeritus of the MGH OBBL, investigated this complication and 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 causing the implant to loosen.
Harris and his colleagues, working with polymer chemists from MIT, created a much more durable material by “crosslinking” the polyethylene. The first-generation highly crosslinked polyethylene was approved by the FDA for use in implants in 1999. However, the first-generation material had limitations in strength that made it unsuitable for some types of joint replacements. Subsequently, Muratoglu was able to chemically stabilize the material. Both mechanical testing and animal studies have shown that the new material resists wear as well as the first generation and is much stronger. This second-generation highly crosslinked polyethylene has also received FDA approval for use in joint implants and was first used as an joint implant on July 16, 2007.
“This material will allow us to offer our patients very 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 implant with the new material. “It should be suitable for higher-stress applications in younger patients, those who are more active and those who are heavier.”