The role of synovial fluid filtration by cartilage in lubrication of synovial joints--I. Mixture model of synovial fluid.

A mathematical model of lubrication of human synovial joints under squeeze-film conditions is presented in this several-part paper. Squeeze-film action leads to a concentration of hyaluronic-acid-protein macromolecular complex in the synovial fluid between the approaching cartilage surfaces as a result of the diffusion of water and low molecular weight substances through the cartilage surfaces or along the gap. Increasing viscosity of synovial fluid delays the approach of these surfaces and the formation of stable gels then protects cartilage, if sliding motion ensues, before fluid film lubrication is restored.