A PARAMETRIC STUDY OF ACETABULAR CUP DESIGN VARIABLES USING FINITE-ELEMENT ANALYSIS AND STATISTICAL DESIGN OF EXPERIMENTS

To isolate the primary variables influencing acetabular cup and interf ace stresses, we performed an evaluation of cup lending and clip suppo rt variables, using a Statistical Design of Experiments (SDOE) approac h. We developed three-dimensional finite element (FEM) models of the p elvis and adjacent bone. Cup support variables included fixation mecha nism (cemented or noncemented), amount of bone support, and presence o f metal backing. Cup loading variables included head size and clip thi ckness, cup/head friction, and conformity between the clip and head. I nteraction between and among variables was determined using SDOE techn iques. Of the variables tested, conformity, head size, and backing eme rged as significant influences on stresses. Since initially nonconform ing surfaces would be expected to wear into conforming surfaces, confo rmity is not expected to be a clinically significant variable. This in dicates that head size should be tightly toleranced during manufacturi ng, and that small changes in head size can have a disproportionate in fluence on the stress environment. In addition, attention should be pa id to the use of nonmetal backed clips, in limiting cup/bone interface stresses. No combination of secondary variables could compensate for, or oven ide the effect of the primary variables. Based on the results using the SDOE approach, adaptive FEM models simulating the wear proc ess may be able to limit their parameters to head size and cup backing .