558 THE JOURNAL OF BONE AND JOINT SURGERY Proteoglycans and Calcification of Cartilage in the Femoral Head Epiphysis of the Immature Rat*

ABSTRACT: The femoral heads of young rats have been used to monitor changes in proteoglycan structure during growth and endochondral ossification. Proteo-glycans were extracted in good yield. The tissue content of proteoglycans increased until the time of calcifica-tion and then decreased. In contrast, the collagen con-tent increased over the period studied. On Day 20, just preceding the onset of calcification, the proteoglycans had a lower glycosaminoglycan content, were some-what smaller, and contained a larger proportion of molecules that were not capable of interacting with hyaluronic acid. On Day 25, during ongoing calcifica-tion, the proportion of proteoglycans that were not ca-pable of interacting with hyaluronic acid was low, while it again was high on Day 40, just preceding os