Water is the most abundant component of normal articular cartilage, making up from 65% to 80% of thewetweight of the tissue.

6,7 A small percentage of this water is contained in the intracellular space, about 30% is associated with the intrafibrillar space within the collagen, and the remainder is contained in the ECM. Water content varies throughout cartilage, decreasing in concentration from approximately 80% at the surface to 65% in the deep zone. Most of the water can be moved through the ECM by compressing the solid matrix. Frictional resistance against this flow through the ECM is very high, and this resistance to water flow within the ECM is the basis of articular cartilage’s ability to cushion very high joint loads.