Differentiating between Load and Displacement Controlled Wear Testing in an Artificial Cervical Disc - A Computational Comparison

Computational Comparison +Bhattacharya, S; Goel V.K; Greenwald A.S +Orthopaedic Research Laboratories, Cleveland, OH, University of Toledo, Toledo, OH [email protected] INTRODUCTION: Osteolysis associated with polyethylene wear has been identified as an important clinical issue with joint arthroplasties [1]. Bench top simulations have emerged as a powerful preclinical tool to predict the wear characteristics of each implant [2]. The current wear standards usually recommend a displacement control mode for testing of artificial discs. These studies are conducted utilizing fixtures and hence do not account for the influence of anatomic structures. It is thus not surprising that wear data based on these laboratory studies, do not match retrievals. In a prior FE based study it was shown that wear characteristics of an artificial disc are affected by the spinal structures and hence they should be simulated experimentally [3]. However if spinal segments are used, a pure moment needs to be applied to ensure that the load does not vary across the length of the segment. This is because the application of displacement can impose complex loads of varying magnitude along the spinal segment. Artificial discs are motion preserving systems so it is unclear if it is appropriate to use “pure moments” or “displacements” for biomechanical evaluations. This current study addresses the aforementioned issue by highlighting differences in wear pattern of an artificial disc using FE technique.