Fundamental fluid transport mechanisms through articular cartilage

A unified self-consistent set of equations governing the fundamental fluid transport mechanisms through articular cartilage is described. These equations include Darcy's law for fluid flow through a permeable medium and Biot's consolidation equations for a fluid-filled elastically deformable permeable solid matrix. Kinematical, mechanical, and geometrical parameters which are important in the understanding of the biomechanics of normal and pathological articular cartilage are identified. Clearly, the present investigation is inchoate in that many of the mechanical and physical constants associated with articular cartilage are as yet unknown and imprecisely defined. Thus only a parametric study has been reported. It was found that in normal, healthy human articular cartilage during normal function the mechanical pumping mechanism dominated the processes of interstitial fluid transport, with the direct fluid pressure mechanism being the mode of fluid transport in the transitory phase of flow reversal. Further, upon load application the interstitial fluid was exuded across the articular surface directly under the load, and upon load removal the fluid was then imbibed under the load. Finally it was found that after one complete cycle there was a very small amount of net flux of fluid into the tissue.