Comparative Failure Analysis of Retrieved UHMWPE Tibial Components

Clinical outcomes and implant survivorship have proven that total joint replacement is one of the most successful performed procedures in the orthopaedic field. Total knee replacement (TKR) has become a fact of life for many people.  Currently more than 43 million people have arthritis, which is the leading cause requiring a TKR.  This prosthesis has become an effective solution for the treatment of knee joint degeneration. Nevertheless, due to the complicated geometry and movements of the knee, the development and improvement of TKRs has been a slow process. Different studies have demonstrated that far too often ultra-high-molecular weight polyethylene (UHMWPE) components sustain premature failure and require replacement. Despite its widespread use, the bearing properties of this polymer continue to limit the wear resistance and the clinical life span of implanted knee prosthetics. Failure analysis was performed to characterize the wear damage sustained by UHMWPE tibial components. The surface damage of three retrieved tibial components removed after the same implantation time period was assessed with semi-quantitative wear damage scoring. The implants were assigned a score from 0 to 210 with 0 being no wear and 210 being more than 50% degradation of the component.  Additionally, the surface morphology of the retrieved components was examined microscopically using stereomicroscopy and scanning electron microscopy to establish failure modes. The scoring method revealed that the degree of damage experienced by the three implants ranged from 119 to 145, which is a relatively wide range despite the fact that the implants had similar implantation times. Therefore, the damage score could not be correlated to the implantation time. One inadequacy of this scoring method is that two of the three retrieved components had similar scores while exhibiting different contact surface degradation mechanisms. Common features to the three UHMWPE components included cold flow, delamination and abrasion.