Equilibrium water partition in articular cartilage.

Water partition between the interstitial fluid in articular cartilage and an external bathing solution was found using a new in-situ method. This consisted of measuring the concentration of radioactive water allowed to diffuse through the articular surface of laterally constrained cartilage-subchondral bone plugs. Incubation times ranged from 15 minutes to 48 hours. Tracer solutions included: Hank's Balanced Salt Solution with and without antibiotics and enzyme inhibitors, and distilled water. Bulk partition coefficients ranged from 0.305 to 0.811. Both the hydration and partition coefficients varied spatially with depth, while no association was found between them. The macromolecular structure of the collagen and proteoglycan components are believed responsible for these findings.