Epiphyseal and physeal cartilage vascularization: a light microscopic and tritiated thymidine autoradiographic study of cartilage canals in newborn and young postnatal rabbit bone.

The vascular pattern of newborn and early postnatal epiphyseal and physeal cartilage is integral to long bone development and differs from later postnatal patterns. In the present study, we supplement light microscopic histology with tritiated thymidine autoradiography to help assess the position of cartilage canals and the dynamics of cartilage vascularity in relation to growth. Tritiated thymidine labeling studies to assess cell proliferation activity were done by using 2 microc/g body weight intraperitoneal injections into newborn and 3-, 4-, and 7-day-old New Zealand white rabbits that were killed 1 hr after the injection. Proximal humeral, distal femoral, and third metatarsal epiphyses were assessed by routine histology and serial section autoradiography. Cartilage canals were seen in each epiphysis. Transphyseal vessels were seen in each epiphysis continuous from the epiphysis to the metaphysis or were present within the physis traversing the proliferating and hypertrophic cell zones. Histologic sections showed vessels from the perichondrium continuous with those of the epiphyseal cartilage canals at proximal humeral, distal femoral, and metatarsal epiphyses. Serial sections showed vascular buds and connective tissue cells lying in indentations at the periphery of and present within the epiphyseal cartilage. Autoradiographic studies showed extensive labeling of vessel wall cells and surrounding connective tissue cells of the cartilage canals (a) within the epiphyseal cartilage, (b) traversing the physis, and (c) within the epiphyseal cartilage but continuous with the perichondrial vessels. The labeling was always far more extensive than in the surrounding chondrocytes and was always present throughout the entire extent of the canals. In conclusion, the cell labeling activity strongly supports an active dynamic phenomenon underlying the vascularization of epiphyseal and physeal cartilage.