Overview of Metal-on-Polyethylene, Metal-on-Metal, and Ceramic Hip Wear Mechanisms

Abstract

Premature failure of orthopaedic hip implants caused by multiple wear mechanisms is the primary failure mode of prosthetic hips. Wearing of the implants may lead to aseptic loosening, biological incompatibilities, and mechanical failure of the implant. In order to prevent or restrict the effects of the wear mechanisms, multiple laboratory studies are being conducted in order to determine each mechanism and its contribution to increased wear rates. This paper combines previous laboratory studies related to the wear of metal-on-polyethylene, metal-on-metal, and ceramic materials. The bulk quantity materials discussed include cobalt chromium alloys, stainless steels, zirconium oxide ceramics, and polyethylene materials that are used in biomedical implantation design, and a summary is provided of the test results of the materials subjected to wear mechanisms. The objective of this study is to present the mechanical properties of bulk materials used in implant design to determine how each mechanical or wear mechanism influences the wear rates for the material. The advantages and disadvantages of each material are also discussed. I. WEAR MECHANISMS There are many factors that influence the wear rates of implant materials. A wear factor or wear mechanism is classified as any mechanism that causes a change in wear rates. The wear rate is determined by the amount of wear that the implant endures with respect to time, and is commonly measured by volumetric loss. It is important to understand that lower wear rates for a specific variable may have been achieved because of the combination of other factors in the given scenario. In order to determine if a variable is a wear mechanism, testing must be conducted to determine if the variable has a significant effect on the wear rate of the test specimen in a controlled environment. 73