Analytical modeling of bone-cement interface and failure prediction

Artificial joint replacement is becoming increasingly important in orthopedics. Several hundreds of thousands of operations, especially of the hip joint, have already been performed. The design of such joints depends largely on how accurately they can be modeled analytically such that their load transmission characteristics can be determined. One of the most critical areas of investigation is the interface existing between bone and implant in the orthopedic prostheses applications. This investigation examines the effect of varying modulus between bone and cement (PMMA) on the failure of the joint. An energy criterion is used rather than the stress criteria normally applied in the open literature.

The results of the present study show that the modulus variation within the interface can have a significant influence on the stress and energy fields in the region near a material interface. It is found that if the interface modulus has a gradual variation, the predicted stress fields resemble those with a single material interface model which has a higher (stiffer) average modulus. The interface modulus variation and average modulus are shown to have a significant effect on the predicted location and onset of failure which is of primary interest. The present modeling scheme is intended to demonstrate some of the effects which might locally be found near the bone and cement interface in a prosthetic joint.