Influence of Synovial Fluid Pressure on Biphasic Lubrication Property in Articular Cartilage

Abstract

The influence of synovial fluid pressure in wedge-film gap on the biphasic lubrication property of articular cartilage during sliding motion has not been discussed in previous studies. We hypothesized that synovial fluid pressure generated in a wedge-film shaped gap just ahead of cartilage contact region suppresses the effusion of interstitial fluid in articular cartilage and that this enhances biphasic lubrication ability of articular cartilage. In the present study, we determined fluid pressure distribution in the wedge-shaped gap. We, then, also performed a friction analysis to compare the coefficient of dynamic friction of standard poroelastic model with that of synovial fluid pressure (SFP) model. In SFP model, the effusion of interstitial fluid from articular cartilage was regulated in accordance with the pressure difference between measured synovial fluid pressure and analyzed interstitial fluid pressure at the surface. Experimental results revealed that the maximum fluid pressure increased with the increase of sliding speed. The coefficient of dynamic friction was lower in SFP model than in standard model with the largest difference of 25% observed at 30 mm/s. Effusion of interstitial fluid from articular cartilage near the periphery of contact region was more suppressed at higher sliding speeds, which resulted in a better lubrication property due to higher interstitial fluid pressurization. These results suggested that synovial fluid plays important roles not only in hydrodynamic lubrication but also in biphasic lubrication by suppressing the effusion of interstitial fluid in articular cartilage.

Keywords

• articular cartilage
• biphasic lubrication
• synovial fluid
• interstitial fluid
• hydrodynamic pressure