The chondrocyte: a cell under pressure.

Mechanical load is an important regulator of chondrocyte metabolic activity. Changes in amplitude or frequency of the load can have a significant effect on the production of matrix macromolecules and of agents leading to cartilage breakdown. The composition of cartilage reflects the net response of the chondrocytes to the prevailing loading pattern, with cartilage proteoglycan content highest in heavily loaded regions and removal of load leading to cartilage thinning and proteoglycan loss. The mechanism of mechanotransduction is poorly understood; the chondrocytes appear to react to cartilage deformation and to the changes in hydrostatic pressure, extracellular ionic composition and streaming potentials induced by the load.