Nonresorbable polymers in bone surgery.

Sufficient strength and stiffness, biocompatibility and long-term stability are important criteria that polymers have to fulfill for successful implant applications in bone surgery. An additional requirement is sterilization without degradation of the polymer properties. Ultra-high molecular weight polyethylene is used as a carrier material in joint replacement components because of good wear and damping properties. Nevertheless, reduction of wear is still a major challenge in polyethylene research as wear particles are responsible for early loosening of prosthetic devices. Acrylic bone cement is used for the fixation of artificial joints, providing an immediate and strong fixation of the implant. Possible problems with this bone cement are the residual (toxic) monomers and the high curing temperature that may cause thermal bone necrosis. Polyacetal resins are implantable high performance polymers. Due to their high chemical and mechanical resistance, they are used in joint replacement components and other long-term implants. Polyetheretherketone is a new and even more stable high performance polymer. Due to its stability at sterilization temperatures and under irradiation, PEEK is intended to replace POM in future. PEEK is available in a "medical grade" quality suitable for long-term implantation.