Volume 2, Issue 7 (July 2005)
Creation of Oxidized Zirconium Orthopaedic Implants
More demanding performance expectations for total joint arthroplasty are driving the development of alternative bearing materials. Oxidized zirconium was developed as an alternative to cobalt-chromium alloy for knee and hip femoral components in order to reduce wear of the polyethylene counterface and to address the needs of metal-sensitive patients. Oxidation in high temperature air transforms the metallic Zr-2.5Nb alloy surface into a stable, durable, low-friction oxide ceramic without creating the risk for brittle fracture associated with monolithic ceramic components. This presentation reviews aspects of this technology with a historical perspective, including standards for the zirconium alloy, non-medical applications for oxidized zirconium, and previous orthopaedic applications for zirconium. Manufacturing processes for oxidized zirconium components are described, beginning with refining of the zirconium from beach sand, to producing the alloy ingot and bar, to fabricating the component shape, and finally to oxidizing the surface and burnishing it to a smooth finish. Conditions are described for producing the oxide with excellent integrity, which is nominally 5 µm thick and predominantly monoclinic phase. The metal and oxide microstructures are characterized and related to the mechanical properties of the components and durability of the oxide. Laboratory hip and knee simulator tests are reviewed, which indicate that oxidized zirconium components reduce wear of the polyethylene counterface by 40–90 % depending on test conditions. As evidenced by promising early clinical experience, oxidized zirconium components have characteristics that provide an alternative to conventional cobalt-chromium components with an interchangeable surgical technique, while providing the potential for superior performance.