ABSTRACT
Tribology is defined as the science that deals with the interaction between surfaces in motion and consequences of that interaction, i.e. friction, lubrication and wear. This chapter aims to define tribology in normal synovial joints and in joint replacements, with reference to corrosion in the latter. Synovial fluid is a dialysate of blood plasma, without clotting factors, erythrocytes or haemoglobin. Studies have shown that fluid-film lubrication dominates in synovial joints. In hydrodynamic (HD) lubrication, there is no contact between surfaces and hence no wear. In elastohydrodynamic (EHD) lubrication, elastic deformation of the bearing surface enlarges the area of the bearing surface and traps pressurized fluid. The micro-elastohydrodynamic (MEHD) lubrication model assumes that the asperities of articular cartilage are deformed under high loads. Boosted lubrication assumes that, under squeeze-film conditions, the water in the synovial fluid is pressurized into the cartilage, leaving behind a more concentrated pool of hyaluronic acid-protein complex to lubricate the surfaces.
