Changes in the hexosamine content and swelling ratio of articular cartilage as functions of depth from the surface.

The hexasamine content and swelling ratio of adult bovine articular cartilage were determined as functions of depth. Progressing from the surface downward, the hexosamine content increased rapidly to a depth equivalent to approximately 30 to 35 per cent of the total thickness of the uncalcified portion of the tissue, and thereafter decreased at a less rapid rate. The swelling ratio was relatively constant throughtout the first quarter of the tissue but diminished thereafter. At depths below 35 per cent, the curve for the decrease in swelling ratio with depth was similar in form to that for the decrease in hexosamine content. Considering the factors that determine the swelling ratio of polyelectrolyte gels, it is proposed that progressing down from the surface, the interaction between the macromolecular components of the tissue is increased to a depth equivalent to about one-third of the total thickness of the cartilage.