ARTHRITIS AND THE INTERACTING MECHANISMS OF SYNOVIAL JOINT LUBRICATION .2. JOINT LUBRICATION AND ITS RELATION TO ARTHRITIS

The lubrication mechanisms involved in synovial joints have remained a mystery for decades. Most research efforts aiming to explain synovial lubrication phenomena and arthritis have relied on the adaptation of existing lubrication theories widely utilized in engineering. As descr ibed in Part I of this paper synovial joints exhibit an intricate stru cture that is extremely sensitive to many internal and external factor s. In Part II, the mechanisms of synovial lubrication by both cartilag e and synovial fluid are discussed in terms of mechanical and physiolo gical concepts. A model of synovial lubrication is presented where fle xure of the joint initiates lubrication by synovial fluid. It is also proposed that the widely varying conditions of loads and sliding speed s found in synovial joints are accommodated by a combination of lubric ation mechanisms involving both synovial fluid and cartilage. A fundam ental difference between an artificial bearing and a living synovial j oint is the significance of metabolic feedback processes to control we ar of synovial cartilage which is far greater than any known analogous processes in artificial bearings. Instabilities in these feedback pro cesses caused by cartilage wear are then reviewed as a basic cause of arthritis.