Wear of a Novel Ceramic on Metal Bearings for Hip Prosthesis

Abstract

Concerns about polyethylene wear debris induced osteolysis has led to renewed interest in alternative bearing couples such as ceramic on ceramic and metal on metal. Conventionally, bearing couples in artificial joints, as well in engineering systems, are comprised of different materials. They frequently have a harder surface and a sacrificial softer surface that wears, for example metal on polyethylene in artificial joints. In alternative hard bearing couples, on like material combinations have been used. While harder materials typically wear less, it is not common practice in tribological systems to design on like bearing couples, as adhesive friction and wear can be high, and both bearing surfaces have the potential for wear. To date, hard bearing couples in artificial hip joints have not been studied as dissimilar bearing materials. Metal on metal bearing couples are attractive from a design perspective, as the material toughness and hardness allows design flexibility, while delivering low wear of the order of one cubic millimetre per year. While the wear volume is low, and at least ten fold lower than cross linked polyethylene, the wear particles are very small, (circa 10 nm), providing a large surface area for metal ion release [1]. Elevated metal ion levels are a clinical concern for patients with metal on metal bearings [2]. Ceramic femoral heads have been extensively used for over thirty years in artificial hip joints and offer a reliable alternative to metallic alloy femoral heads. In this study alumina ceramic femoral heads were paired with metallic acetabular cups producing a novel differential hardness hard bearing couple. We report the wear performance of this novel differential hardness ceramic on metal bearing couple [3] and compare it with conventional metal on metal bearings.