Biocompatible alumina ceramic for total hip replacements

Their resistance to wear and biocompatibility make ceramics ideal materials for medical applications, such as implants. For over 30 years, pure alumina has been the dominant material for ceramic hip prostheses. Interest in alumina hip prostheses continues to grow, due to the relatively short life of polymer/metal prostheses, mainly resulting from osteolysis and aseptic loosening caused by polymer wear debris. Since its introduction by Boutin in the 1970s, substantial improvements have been achieved in the microstructure of medical grade alumina by improving purity and processing to give complete densification and fine, uniform grain sizes. A brief review is given of the types of alumina used in total hip replacement, the development of medical grade alumina, and methods of in vivo and in vitro investigation of alumina prostheses, with a focus on current knowledge of the damage observed on alumina prostheses. Particular attention is paid to wear mechanisms and the influence of materials properties on wear behaviour. A region of relatively severe wear, known as stripe wear, is widely observed on retrieved alumina hip prostheses. This type of wear can now be replicated in vitro in joint simulators by the introduction of a 'microseparation' motion during the test cycle. Finally, the future of ceramic hip prostheses and development of the next generation of ceramics for hip prostheses is discussed.