Wear Properties of a Pyrolytic Carbon Intervertebral Disc Replacement

*Cheema, N; +*Salkeld, S; **Hawkins, N; **Bailey, K; *Cook, S +*Fellowship of Orthopaedic Researchers, Inc., Metairie, LA [email protected] INTRODUCTION: The purpose of this study was to determine if particulate pyrolytic carbon debris was generated during wear simulation of the Regain™ lumbar nuclear disc replacement articulating on cortical bone. The Regain device is fabricated from pyrolytic carbon and is designed to articulate between the cartilaginous endplates of the vertebral bodies in the lumbar spine. Pyrolytic carbon has been established as a highly biocompatible material for prosthetic use following several decades of implantation history in finger joint and heart valve prostheses. Its mechanical strength is three to four times that of cortical bone and has an elastic modulus similar to that of bone. These factors allow for exceptional mechanical compatibility and stress transfer. Additionally, pyrolytic carbon does not exhibit fatigue failure as observed with metallic materials and is highly resistant to wear. In vivo studies in dogs and primates have demonstrated excellent wear properties when articulating on cartilage in which cartilage was maintained rather than lost over time. For this study, a unique process was developed in which a custom wear simulator articulated the Regain™ against bovine cortical bone in a physiological lubricating solution, thereby simulating the worst-case clinical scenario of complete endplate cartilage loss. The lubricating solution was then subjected to a digestion process to eliminate serum salts, proteins, and bone debris. This allowed for the number and size of pyrolytic carbon debris particles to be counted using a laser particle counter. Thus, the traditional method of analyzing wear rates of hip and knee prostheses, which relies on the quantification of weight change of the device over the course of a simulation, is not necessary.