Paper 7: Properties of Synovial Fluid

Synovial fluid functions both as a lubricant and as a nutritive medium in joints. Its chemical composition suggests that it is a dialysate of blood plasma with the addition of the mucosubstance, hyaluronic acid. In addition the fluid contains a small cellular component. The quantities of some of the chemical components are apparently anomalous and need explanation. The hyaluronic acid, probably combined with a small amount of protein, is believed to be secreted by the cells lining the joint cavity, the synovial cells.

The volume and naked eye appearance of the fluid vary from joint to joint in the same species and in the same joint from species to species. The volume of fluid that can be aspirated from normal human joints is too small for most chemical and physical investigations and recourse must be made to fluids from the larger domestic animals and to pathological human fluids.

The most characteristic property of the fluid is its viscosity. This has been investigated using the Weissenberg rheogoniometer. This allows of a study of the viscosity and elasticity of the fluids at different shear rates. Results on fluid from both normal animal joints and pathological human joints will be presented. Their relevance in joint lubrication will be discussed.