NUMERICAL ANALYSIS OF SQUEEZE FILM LUBRICATION ON HEALTHY AND OSTEOARTHRITIC KNEE JOINTS

Abstract

The synovial joint of the knee can be affected by diseases, such as arthritis or osteoarthritis, being a knee replacement the selected clinical solution in irreversible cases. This work is aimed at investigating lubricated contact in healthy and pathological knees, with the aim of achieving knowledge that can be used to delay knee replacement. The equivalent geometric model of a rigid ellipsoid on a deformable plane is adopted, where the synovial fluid is considered to be Newtonian and the articular cartilage is a linear elastic material. Studies were carried out varying the modulus of elasticity E of the cartilage, its thickness e and the viscosity of the synovial fluid , adopting values corresponding to healthy and osteoarthritic natural joints, in order to evaluate their influence on the functioning of the joint considering squeeze film lubrication. Compared to what was obtained for a healthy joint, the decrease in the elastic modulus E would not have a significant influence on the minimum lubricant film thickness, while the decrease in cartilage thickness would improve said thickness. The decrease in viscosity decreases the minimum thickness of the lubricating film by 65 %, so viscosupplementation would increase the viscosity, which would also increase said thickness and prevent wear of the articular surfaces. A decrease in cartilage thickness or in cartilage module would produce a decrease of the cartilage tensions. On the other hand, a decrease of viscosity produces an increase of these tensions. In a pathological joint (where the fluid viscosity and the cartilage thickness and elastic module are diminished), and considering a load of 800 N, the minimum film height, the maximum pressure and the maximum Von Mises tension obtained are 66 %, 22 % and 28 % respectively lower than those observed for a healthy articulation.