Wear phenomenon of ceramic joints.

Ceramic materials offer a number of beneficial mechanical properties such as considerable hardness, good chemical resistance, high tensile strength and good fracture toughness. The use of ceramic-onceramic as bearing surfaces for hip joint prostheses has been reported to produce a lower wear rate than other material combinations in total hip arthroplasty. These advantages may increase the life expectancy of hip implants and improve the life of patients. To date, more than 2.5 million alumina femoral heads have been implanted. Material scientists have progressively improved the mechanical strength of alumina, leading to three subsequent generations of medical-grade alumina. A significant effort was devoted to the development of composites such as zirconiatoughened alumina, with the aim of combining the best characteristics of alumina and zirconia. This new class of composite material was introduced in 2004 and is known under the trade name of Biolox® delta. Biolox® delta has 10 years of clinical records in hip replacements and is beginning to be used in knee replacements. Improvements in material manufacturing have decreased the failure rate of second- and thirdgeneration alumina. Retrieved alumina-on-alumina hip prostheses have revealed a small band of wear around the rim of acetabular cups, due to the microseparation phenomenon. Introducing microseparation into in vitro wear simulator tests, the wear rates, patterns and mechanisms observed in vivo may be successfully reproduced.