Progressive Wear Damage Analysis on Retrieved UHMWPE Tibial Implants

Abstract

In recent years, the incidence of knee joint degeneration has increased considerably in the 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 and numerical 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 led to wear debris formation. A failure analysis was performed to examine the progressive wear damage sustained by UHMWPE tibial components. The surface damage of six retrieved tibial components was assessed with a semi-quantitative wear damage scoring. Additionally, the surface morphology of the retrievals was examined microscopically using stereo- and low voltage scanning electron microscopy to explore the relationship between in vivo surface damage mechanisms and large-deformation plasticity. The semi-quantitative wear scoring method revealed that the damage experienced by the six studied retrievals ranged from 19 to 136; nonetheless, the score damage could not be correlated to the implantation time due to the lack of complete background information provided on each patient. One inadequacy of this scoring method is that two the retrieved components had similar scores but demonstrated different contact surface degradation mechanisms. For instance, one of them displayed severe pitting while the other revealed an absence of pitting. Their common features included deformation, delamination and abrasion.