[Wear and loosening of prostheses]

In 1996, the outcome of any total joint replacement is loosening, occurring usually about 20 years after implantation. Loosening is not a mechanical failure of the bone-implant junction but the consequence of the osteolysis of the periprosthetic bone. It is due to an inflammatory pannus, a tissue constituted by macrophages, which are activated by wear particules originated by the articulating surfaces. The authors showed that this osteolysis is close from that observed with other inflammatory diseases and that it can be obtained with wear particules of many biomaterials, the polyethylene (PE) being the most common in clinical conditions. Several trends in order to reduce polyethylene wear or to replace PE by other materials are presented. Future improvements of the duration of joint prostheses depend on laboratories including surgeons involved in basic research: they are a mandatory link between the engineer and the biologist who study the mechanical and the biological aspects of the wear and of the fixation of biomaterials.