Analysis on the Elastohydrodynamic Lubrication of Knee Implant Using a Line Contact Model under Simulated Walking Conditions

In this paper, a time-dependent analysis on elastohydrodynamic lubrication (EHL) in the knee-joint pair was carried out using a line contact model. Both load and speed were considered as cyclic functions representative of normal walking. A numerical method was developed to solve the equations with a multi-grid solver, in which the bearing surface deformation was obtained from elastic equation of a semi-infinite plane. The variations in predicted pressure distribution and film thickness profile with time were observed under different conditions. The results showed that the variation in the predicted central pressure was similar to the variation of load in a gait cycle, and the change of equivalent radius can make a significant change in the predicted central pressure. In the stance phase, the film thickness gradually decreased with fluctuation because of the combined effects of the entrainment and squeezing film actions. In the swing phase, however, the variation in the film thickness was only related to entraining velocity for the constant load. Furthermore, it is pointed out that a reduction of the tibial radius was of benefit to the lubrication film thickness, while a gait cycle extension may be harmful to the film thickness.