Further studies on the composition of human femoral head cartilage

This report continues our previous studies on the composition and swelling of articular cartilage. When the protein part of the proteoglycan moiety has been taken into consideration, there is no longer a large fraction of the tissue which is not accounted for. In fact, the collagen, proteoglycans, and free electrolyte represent over 92% of the dry weight of adult femoral head cartilage, the remainder consisting most probably of other glycoproteins. Once the composition of cartilage had been well defined, it was possible to calculate the overall wet volume of tissue per unit weight of collagen for both normal and osteoarthritic cartilage. This is an important parameter, as it constitutes a direct measure of the extensibility of the collagen network. By determining the fixed charge density profile close to the articular surface, we have also been able to estimate the swelling pressure due to the proteoglycans in this region of the tissue, and to show that there is a gentle grading of osmotic stresses.