Modelling of fluid support inside articular cartilage during sliding

Considerable attention has been drawn to the lubricating mechanism of synovial joints. Biphasic lubrication was proposed by Mow and Lai [1] based on the load partitioning mechanism between fluid and solid phases of articular cartilage. Forster et al. [12] carried out experimental studies to investigate the same, whereas Ateshian et al. [13, 17] further investigated it theoretically using interstitial fluid pressurization. Forster and Fisher [15] showed that start-up frictional coefficient was higher than that under a wide range of sliding conditions and that biphasic nature of the cartilage does play a significant role in joint lubrication. The experimental and theoretical studies of frictional behaviour of the cartilage have been carried out by several researchers; however, finite-element modelling is far less in comparison, and mainly focused on deformation rather than sliding conditions. In the present study, two finite-element models were developed to study the effect of sliding on fluid load support in the cartilage and its implications to frictional and lubricating characteristics. The results predicted by the static model were same as those given by a metallic plate sliding over the cartilage surface, whereas the model of a metallic cylindrical indenter sliding over the cartilage surface with the migrating contact area showed remarkably higher fluid load support for relatively long-time durations. The results agreed with the experimental results presented by Forster and Fisher [15] and Bell et al. [24] and, in general, with those of other researchers with respect to weeping, boosted, and self-generating lubrication mechanism. Further extensive studies need to be carried out to compare the finite-element prediction with the experimental studies under other conditions.