Trabecular generation de novo. A morphological and immunohistochemical study of primary ossification in the human femoral anlagen.

An understanding of trabecular formation in early skeletal development may provide insight into the problem of trabecular replacement in the aging skeleton. In an optical and scanning electron microscope study of the processes of de novo trabecular generation, the immunohistochemical distribution of collagen Types I, II and III, together with the matrix organising proteins fibronectin and tenascin, has been examined in the ossifying human femoral anlage. In the region of the developing spongiosa, the primary osseous trabeculae that arose by endochondral ossification were assembled around calcified cartilage remnants, consisting almost entirely of aggregates of mineralised microspheres. These structures were specifically recognised by antibodies raised against collagen Type II and fibronectin. In contrast, the primary osseous trabeculae that arose by subperiosteal intramembranous processes, were assembled around a framework of prominent coarse fibres that were recognised by antibodies raised against collagen Type III and tenascin. Irrespective of their origin, all the new trabeculae were similar in their general staining character for collagen Type I and fibronectin. However, throughout the developmental stages examined here endochondral trabeculae were separated from intramembranous trabeculae by a discrete boundary of compressed cells and mineralised cartilage.