Stress distributions in the acetabular region--II. Effects of cement thickness and metal backing of the total hip acetabular component.

A two-dimensional finite element study was undertaken to establish the stresses in the acetabular region after total joint replacement. The influence of cement thickness and the effect of metal backing on the polyethylene cup were explored. Increasing cement thickness (from 1 to 3 to 5 mm) caused a decrease in the von Mises' equivalent stresses in the cement and surrounding cancellous bone. A more dramatic reduction in these stresses was found when a 2 mm thick cobalt-chromium alloy backing was added to the cup. The results indicate that increasing the stiffness of the composite implant by either method is helpful but that the metal backing causes a more efficient transfer of the stresses to the walls of the ilium. The finding strongly suggests that the use of a metal-backed acetabular component will help to delay or prevent cup loosening and migration in total hip replacement patients.