Uncalcified cartilage resorption in human fetal cartilage canals.

In the human fetus, epiphyses appear as a solid avascular cartilaginous mass until the eleventh week of development. Around the third fetal month of development, vascular canals coming from the perichondrium are recognized in the mineralized epiphyseal cartilage. Whether cartilage canals develop by passive inclusion or active chondrolysis is still a matter of controversy. We studied the relationships between the intracanalar cells and the surrounding matrix on human fetal epiphyses embedded in glycol methacrylate. At the blind end of canals both stellate fibroblast-like cells and vacuolated macrophages are observed. These cellular foci show all characteristics of active chondrolysis (loss of metachromasia, lacunae containing cells intimately associated with matrix, and presence of granular debris). Similar resorptive foci have been observed in the pannus of rheumatoid joints and in the embryonic chick growth plate composed of uncalcified cartilage. A cellular cooperation (fibroblast/macrophage) is necessary for uncalcified cartilage breakdown. In the human fetus, monocytes/macrophages have been recognized in the peripheral blood as early as the twelfth week of gestation. Our observations support the view that chondrolysis due to both fibroblasts (of mesenchymal origin) and macrophages is the basic mechanism for cartilage canal development.