Heterogeneity of the cartilage-marrow interface during uncalcified cartilage resorption in the chick embryo tibia.

The morphology of the cartilage-marrow interface in chick embryo tibiae has been studied from Day 11 to Day 14. The cartilage-marrow interface did not present a uniform aspect and three different areas could be defined. Most of the interface was lined by fibroblast-like cells, macrophage-like cells and multinucleate giant cells. Other areas were characterised by a paucity of cells and by the presence of much cell debris. In focal areas the cartilage surface was excavated and covered by several layers of closely packed cells. These cells presented longitudinal axes perpendicular to the cartilage surface and were characterised ultrastructurally by the presence of large amounts of rough endoplasmic reticulum and large cytoplasmic processes extending into the matrix. The presence of different cell associations along the cartilage-marrow interface seems to suggest that uncalcified cartilage resorption follows a phasic pattern.