Chemical composition and swelling of normal and osteoarthrotic femoral head cartilage. II. Swelling.

Studies of the equilibrium, partition, and diffusion of tritiated water were carried out on normal and osteoarthrotic cartilage as well as on cartilage from which proteoglycans had been extracted chemically. All the water was found to be freely exchangeable in both normal and degenerate specimens. The diffusiviity of the water was equal to about 40% of the value in free solution, with an activation energy equal to that in free solution. It was concluded that the swelling of degenerate tissue is not due to any changes in the state of the water, but to a failure of the damaged collagen network to oppose the swelling pressure of the proteoglycans. Swelling similar to that observed in fibrillated cartilage was also found in initially normal specimens treated with collagenase.