The lubricative function of artificial joint material surfaces by confocal laser scanning microscopy. Comparison with natural synovial joint surface.

The purpose of this study was to observe and compare the effect of the behavior of different lubricating surfaces, including articular cartilage and several artificial joint materials, under the physiological loading by confocal laser scanning microscopy (CLSM) to clarify the mechanism of lubrication in natural joints and subsequently improve the quality of artificial joints. In our experiment, even with considerable loading, natural articular cartilage exhibited a synovial fluid area and an area of direct and solid contact. In the region between these two areas, a liquid crystal layer was observed. On the other hand, the materials used for artificial joints (metal and polyethylene, which are now in use, and polyvinyl alcohol-hydrogel polymer which is being developed), did not exhibit neither a clear fluid pool area nor the intermediary area with liquid crystal formation. These results suggest that natural articular cartilage surface has a particular characteristic which builds up a synovial pooling area and liquid crystal formation in the third area by interaction with macromolecules in synovial fluid under the loading condition. These characteristics give natural articular cartilage its excellent lubricative function. To improve the quality of artificial joints, the characteristics of the implant material surface and the synovial macromolecules must be considered.