Influence of the contact model on the dynamic response of human knee joint

Abstract

The main purpose of this work was to study how the contact model influences the dynamic response of the human knee articulation. The knee model, developed under the framework of multibody methodologies, is composed by two rigid bodies, the femur and the tibia, and by four nonlinear springs, which represent the main ligaments of the knee. In order to provide a dynamic activity to the model, a sinusoidal external force is applied at the tibia center of mass. Several computational simulations were performed with the purpose to test and compare several contact modeling parameters, such as the contact law, the geometrical and material properties of the contact bodies. The contact laws considered here are the Hertz law, the Hunt-Crossley model and the Lankarani-Nikravesh model. This study showed that Hertz model is less appropriate to describe the dynamic response of cartilage, because it does not take into account the cartilage viscoelastic nature, which is the responsible for the cartilage ability to shock absorption. Because the tibiofemoral contact can exhibit conformal and non-conformal scenarios, three distinct geometrical models for femur-tibia were considered: convex sphere-plane model, convex-convex spheres model and convex-concave spheres model. Based on the obtained results, it can be drawn that the level of contact forces is higher for the conformal scenario. Concerning to the influence of the properties of the contact materials, the dynamic response of the healthy knee was compared to three pathologic and two artificial knees. The obtained results demonstrated that the cartilage reduces the peak force experienced by the models without cartilage and extend the impact loading period over a longer time.