Effect of Synovial Fluid Pressurization on the Biphasic Lubrication Property of Articular Cartilage

Abstract

The wedge-film and squeeze-film effects have been evaluated as a mechanism of hydrodynamic lubrication without considering the relationship to the interstitial pressurization in biphasic lubrication. We hypothesized that the synovial fluid pressure generated by articular motion suppresses the exudation of the interstitial fluid, enhancing the biphasic lubrication ability of articular cartilage. To verify this hypothesis, the effect of the synovial fluid pressure generated by the wedge-film effect was investigated, and in our previous study, it was found that the synovial fluid plays an important role in hydrodynamic lubrication and biphasic lubrication. In this study, the effect of fluid pressurization generated by the squeeze-film effect on biphasic lubrication was evaluated. First, we measured the pressure distribution in the squeeze-film fluid sandwiched between a plate and an approaching cylindrical polyurethane indenter. Second, a synovial fluid pressure (SFP) articular cartilage model was created in Abaqus based on our previous study, where the exudation of the interstitial fluid from articular cartilage was regulated depending on the pressure difference between the interior and exterior of the cartilage. Third, the fluid load support in the cartilage model was analysed at contact. The results revealed that the squeeze-film pressure increased with increasing approach speed. The fluid load support ratio of the SFP model was higher than that of the standard model at approach speeds of 1, 5 and 10 mm/s. The synovial fluid pressure, induced by the squeeze-film effect, influences the biphasic lubrication property of articular cartilage.