Total joint replacement is an established treatment for severely impaired joints. Significant complications persist, however, which are directly influenced by fracture processes occurring in the interfacial structures found in total joint replacement systems. The purpose of this research is to establish failure criteria for these structures using the principles of fracture mechanics. The specific problem to be studies is surface damage occurring on the polyethylene surface of the tibial component in total knee replacement as a result of articulation with the metal femoral component. Failure criteria governing the occurrence of the problem will be experimentally established. Stress analysis will be performed to determine the stresses arising within the implant system which would lead to failure. These stresses will be examined as a function of the implant geometry. Fracture analysis will then be performed to show that variations in component geometry will affect the propensity for failure. This analysis will employ the experimentally determined failure criteria. The goal is to demonstrate that design variables can be chosen to minimize the occurrence of such failures without adversely affecting other aspects of implant function. In this way, the longterm performance for total joint replacement will be improved.