Boundary Lubrication in Natural Articular Joints

This review concentrates on studies into the behaviour of natural articular cartilage under boundary lubrication. This includes investigations into the chemical composition at the surface of cartilage, carried out as a means of identifying the boundary lubricant. Studies on the friction of cartilage sliding against cartilage and cartilage sliding steel or glass under conditions expected to be in the boundary regime are described. Additionally, model studies on the possible mechanisms of boundary lubrication using well-defined artificial surfaces are also discussed. Although there appears to be some contradiction between the results of friction measurements, an explanation can, at least in part, be given in terms of the layer of cartilage that is being measured. The different chemical nature and lubricating behaviour of the layers found at or near the surface are discussed in relation to the various results given in the literature.