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.
An advance over first-generation highly crosslinked polyethylene, which was also developed at 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 Orthop,dics 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, now 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 , a condition called periprosthetic osteolysis.
Harris and his colleagues, working with polymer chemists from MIT, found that high doses of radiation would crosslink the polyethylene, bonding molecules together to produce a much more durable material. The procedure also generates free radicals that could lead to oxidization and degradation of the implant, but the research team found that melting the material would eliminate free radicals. The first-generation highly crosslinked polyethylene was approved by the FDA for use in implants in 1999 and has been licensed to Zimmer, Inc.