THE ROLE OF BACKSIDE POLISHING, CUP ANGLE, AND POLYETHYLENE THICKNESSON THE CONTACT STRESSES IN METAL-BACKED ACETABULAR COMPONENTS

Mechanical interactions between the polyethylene liner and the metal-b acking play an important role in the load transfer and debris-generati on mechanisms of an acetabular component. Insert thickness, cup orient ation, and insert-shell interface conditions affect the resulting cont act stresses at the articulating and backside surfaces of the polyethy lene component. The objective of this study was to determine the varia tion in contact stresses on a hemispherical acetabular component as a function of the friction coefficient of the liner-shell interface, the thickness of the insert, and the load application angle. Three-dimens ional finite element models of a metal-backed acetabular component wit h liner thicknesses of 3-12 mm were developed. The insert-shell interf ace was modeled as either matte or highly polished, and the load angle of the joint reaction force was changed from 36 to 63 degrees with re spect to the dome. We found that the contact stresses at the articulat ing and backside surfaces of the insert were relatively insensitive to changes in the coefficient of friction at the insert-shell interface (resulting in similar to 1-10% variation in contact stress), when comp ared to the effect of changing the insert's thickness (similar to 80% variation in contact stress) or changing the direction of the joint re action force (similar to 20% variation in contact stress). The results of this study suggest that polishing the metal at the insert-shell in terface does not substantially change the contact stresses at either s urface of the component. Of the design variables available for selecti ve modification by either the surgeon or the engineer, insert thicknes s and shell orientation play a greater role in determining the magnitu de of the resulting contact stresses. (C) 1997 Elsevier Science Ltd.