Fluid compartmentation and articular mechanoreceptor discharge in the cat knee joint.

Experiments were performed to determine the effect of alteration of intra-articular pressure in different areas of the cat knee joint on the discharge of slowly adapting mechanoreceptors in the posterior region of the joint. At physiological (subatmospheric) pressures the anterior and posterior regions of the knee joint are not hydraulically continuous. However, at supra-atmospheric pressures between 2.5 and 9 cmH2O there is free communication between these areas. The discharge of receptors in the posterior region of the joint is influenced by intra-articular pressure changes in the posterior region when these are supra-atmospheric. However, pressure changes in the anterior region of the joint have little effect on the discharge of these receptors until free communication occurs between anterior and posterior regions. It is suggested that articular mechanoreceptors detect tension changes in collagen fibrils rather than volume changes of the joint capsule.