Wear characteristics of a novel bearing system for artificial knee joint (Micro-pocket-covered femoral component and tibial poro-elastic-hydrated cartilage)

Abstract

This paper presents an experimental investigation upon the wear characteristics of a novel bearing system proposed for the artificial knee joints. Such bearing system is original in the meaning that micro-pockets are machined on surface of the rigid femoral component; a poro-elastic-hydrated layer, called artificial cartilage, covers the rigid tibial substrate. Under compression, the fluid exudes from the artificial cartilage, fills and pressurizes the micro-pockets. In this way, a poro-elastohydrodynamic regime of lubrication is developed. Wear tests are performed with different types of artificial cartilages made in PVA hydrogel, articulating against smooth and micro-pocket-covered femoral components. Influence of the number of walking cycles, femoral porosity, depth of the micro-pockets, water content and polymerization degree of the PVA hydrogel upon its wear factor is illustrated. For wear tests performed until 106 walking cycles, in the case of PVA hydrogel with 12 300 polymerization degree and 77% water content versus smooth component, the wear factor is on order of 10-6 - 10-5 mm3/Nm ; for the same artificial cartilage against a femoral component uniformly covered by identical micro-pockets of 50 μm depth, on 15% of its surface, the wear factor drops in the range 10-7 - 10-6 mm3/Nm, i.e., the wear factor reduces with 80%. The highest wear reduction due to the micro-pockets presence is obtained in the case of PVA hydrogel with 77% water content, i.e., for a fluid amount similar to that of the natural cartilage.