Effect of holes in metal backing on polyethylene stresses in acetabular cups: A three-dimensional finite element stress analysis

A three-dimensional finite element model was used to study the effect of screw holes in the metal backing of acetabular components with inset polyethylene liners. The model included the polyethylene liner, the metal backing with empty screw holes, the interface between the polyethylene and metal backing, and the supporting bone. As expected, it was found that screw holes in the metal backing had a significant effect on stresses in the polyethylene. High stress concentrations occurred in the polyethylene liner in the vicinity of the holes, particularly when the holes were in direct line with the joint load. The reduction of polymer thickness from 10 mm to 6 mm increased the stress near the screw holes by approximately 45%. Stresses were markedly reduced (by a factor of 2) when the cup was oriented so that the screw holes were not directly aligned with the applied joint load.