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Two long-term wear behavior studies used in part of the process of selecting the best materials for a new all-metal orthopaedic spinal implant are presented. The relative and absolute wear volume rates of candidate metals were investigated through simulation of two bearing regions of an intervertebral disc prosthesis. It was determined gravimetrically that hot isostatically pressed Co-Cr-Mo alloy provided the lowest Co-Cr-Mo alloy wear debris generation. It had an average wear volume rate of 0.093 mm3/million cycles from a spring-in-pocket simulation and 0.126 mm3/million cycles from a hinge (pin-in-slot) simulation. The estimated total wear volume of a hot isostatically pressed intervertebral disc prosthesis with titanium-6%Al-4%V alloy springs was 2.9 mm3/million cycles.

This article presents criteria for the design of a lumbar intervertebral disc prosthesis that take into consideration issues of endurance, materials behavior, geometry, kinetics, motion constraints, fixation to bone, and safety. The criteria and design philosophies discussed are generally applicable in the synthesis of any new implant system. Specifications of the design of a disc prosthesis are presented along with an evaluation of the design based on some of the preliminary test data.