Subluxation of the Carpal Scaphoid

Discussion and Conclusions In view of the fact that the decay of oscillation of the pendulum was linear we conclude that, for the periods of time, frequency of oscillation and loads examined, no fluid film was present between the cartilage surfaces under load. The fact that removal ofsynovial fluid increased the coefficient of friction suggested that synovial mucin was acting as a boundary lubricant. (Theoretically, the variation with shear rate of the viscosity of synovial fluid might be such as to give a shear force independent of velocity, thereby simulating boundary lubrication. In practice, the chance that the requisite relationship between shear rate and viscosity obtained in all the joints examined, at three different loads, is extremely remote.) Since treatment with defatting agents markedly increased the coefficient of friction in all joints, we conclude either that the extracellular fat in articular cartilage is a lubricant for the joint, or that an adsorbed layer of mucin was still present after the cartilage surfaces had been wiped (with tissues) and that all three defatting agents interfered with its adsorption or physical properties. Alternatively, these two mechanisms could both be operative. These possibilities are being studied further.