1 Copyright © 2011 by ASME Proceedings of the ASME 2011 Summer Bioengineering Conference SBC2011 June 22-25, 2011, Farmington, Pennsylvania, USA SBC 2011- 53027 THE EFFECT OF DIFFERENT MATERIAL COMBINATIONS ON WEAR OF AN ARTIFICIAL CERVICAL DISC AS STANDALONE VS. PLACED IN A LIGAMENTOUS MOTION SEGMENT Bhattacharya, S; Goel, V.K*; Kiapour, A; Liu X *VGoel@utnet.utoledo.edu Engineering Center for Orthopaedic Research Excellence (ECORE), Department of Bioengineering and Orthopaedic Surgery, Colleges of Engineering and Medicine. University of Toledo, Toledo, OH INTRODUCTION Earlier efforts in areas of hip and knee arthroplasties suggest that wear debris, especially from polymeric components, could initiate inflammatory responses leading to peri-prosthetic osteolysis and bone resorption at the implant-bone interface. Aseptic loosening of implants due to particle induced osteolysis is the primary cause of revision surgeries. Metal based implants are considered superior in terms of wear resistance. 1-2 However metal-on-metal articulation leads to much smaller sized particulates in comparison to metal-on-polymers. Thus for an equal volume of wear debris from both polymer and metal, the number of metallic particulates can be up to 100 times greater 3 . Accumulation of metallic debris in the periprosthetic tissue leads to the formation of a fibrous membrane, which might act as a channel for polymeric particulates 4 . Bench top wear tests as well as bioreactivity studies have emerged as a powerful preclinical tool. However there is still a gap between the in vitro bench-top wear tests and the retrieval test cases. Additionally, these experiments are time consuming, expensive, and labor-intensive procedures. In spite of the fact that experimental data are indispensable, alternatives need to be explored. Predictive finite element modeling based on wear- laws serve as an excellent design tool for parametric analyses. In such models, the effect of individual variables can be judged independently leading to an understanding of the role of that parameter on the final outcome. Comparative wear data for artificial cervical discs are sparse. The purpose of this study is to characterize the wear performance of a metal-on-metal (MM) ball and trough artificial disc and compare the wear performance of this device to metal-on-polymer (MP) ball-on-trough artificial disc in an in-vitro and in-vivo simulation using FE modeling. Our hypothesis is that wear rates and patterns in an in-vivo scenario differs from machine simulated data and is also dependent on the material combination chosen. METHODS Two cases were simulated for each device, Disc alone and disc placed within a motion segment (Disc+FSU). FE models of artificial cervical discs (metal on polymer design (MP) and metal on metal design (MM) were created in Abaqus TM FE package (Fig1). Both of these designs were ball and trough type. It should be noted that the inferior trough was assigned properties of polymer. The properties of polymer and metal was Y=1400MPa, ν=0.46 and Y=220 GPa, ν=0.32 respectively. Flexion/Extension of±7.5°, Lateral Bending of ±6°and Rotation of ±4° via time-dependent amplitudes within a single loading step were applied along with a varying preload of 50N-150N at 1Hz as per ISO18192. The contact surface was assigned a sliding interaction with appropriate coefficients of friction of 0.05 and 0.2 respectively for MP and MM respectively. A subroutine based on Archard’s law simulated the abrasive wear for up to 10 million cycles; wear coefficient was derived from literature. 1-2 For the Disc+FSU model, discs were placed in an experimentally validated ligamentous C5-C6 FE model. This model was also subjected to a preload (follower load to simulate the effect of muscles) , followed by various degrees of rotations to simulate wear (Disc+FSU), Fig 1. Fig 1: FE based Disc and Disc+FSU wear models for the (A) metal on polymer (MP) and (B) Metal on metal (MM) discs.