Compliant Tibial Stem for Primary Total Knee Arthroplasty

Objective: Total knee arthroplasty (TKA) is a common and highly successful treatment for knee osteoarthritis. Despite its success, some TKA implants still do not last the remaining lifetime of the patient, due in large part to aseptic loosening of the bone-implant interface, most commonly involving the tibial component. In this manuscript, we present a compliant tibial stem with the potential to increase the lifespan of TKA by accommodating rotation of the tibial tray about the tibia’s long axis without introducing an additional high-cycle-count wear surface. Our objective was to refine the design of this implant to support the loads and displacements associated with common activities of daily living (ADLs), and to validate performance of a physical prototype on the benchtop. Methods: We used finite element analysis to sweep a representative parameter space of reasonably-sized caged hinges, and then to refine the mechanism geometry in the context of in vivo knee joint loads. We fabricated a prototype of the refined mechanism, and evaluated performance of that physical prototype under ADL loads and displacements. Results: The refined mechanism supports walking loads and displacements with a safety factor of 1.47 on the target fatigue stress limit. The maximum reaction moment in the prototype was 1.22 Nm during emulated walking, which represents a reduction of approximately 80% from the in vivo reaction moment within a conventional TKA implant rotating to the same angle. Discussion/Conclusion: Our results demonstrate feasibility of a compliant tibial stem with the potential to decrease failure rates and increase longevity of TKA implants.