Computational Wear Damage Analysis on Retrieved Tibial Components

Abstract

In recent years, the incidence of knee joint degeneration has increased considerably in young and elderly population. Due to the complicated geometry and movements of the knee, the development and improvement of knee joint prostheses have been a slow process that includes not only in vivo and in vitro studies, but also, computational analysis. Different studies have demonstrated that far too often ultra-high-molecular weight polyethylene (UHMWPE) components sustain premature failure and require replacement. In spite of its widespread use, the bearing properties of this polymer continue to limit the wear resistance and the clinical life span of implanted knee prosthetics. UHMWPE is subjected to complex-multi-axial stress states in vivo causing multiaxial shearing at the articulating surfaces, which in turn, has lead to wear debris formation. Characterization of UHMWPE retrieved tibial inserts with implantation times up to 20 years was performed to identify damage areas and the relative deterioration severity. Additionally, several computational models were used to determine contact areas between the femoral implant and the polyethylene component and to analyze deformation of the latter. The modeling of all knee joint components was also completed to simulate, as close as possible, a realistic interaction between the assembly components. The components were tested with compressive and bearing loads with magnitudes up to 11kN, representing four different activities (walking, squatting, rising from a chair, and stair climbing). The damage regions predicted by the simulations were in excellent agreement with those observed on the central portion of each implant contact surface. Nonetheless, small posterior damage regions observed analytically were not present on the retrieved components, possibly due to problems with components positioning in vivo or the input kinematics in the model.