Techniques of tissue exclusion have been used previously in qualitative investigations of the vascularity of long bones, after experimental fracture; we quantified their effects on bone blood flow in rabbits. Thirty-six adult rabbits were divided into three groups in which flow was measured, with the microsphere technique, 1 and 2 weeks after osteotomy. In Group 1, osteotomy of the tibial shaft only was done; in Group 2, osteotomy was done with exclusion of the periosteum and muscle by a silicone rubber sheath; and in Group 3, osteotomy was done with exclusion of the marrow by reaming and insertion of an intramedullary nail. All involved limbs were immobilized in a cast. In Group 1, cortical flow increased but marrow flow did not change, which suggests that the changes in cortical flow were mediated by a supply paralleling that of the marrow. In Group 2, the changes in cortical flow were abolished, which implies that this parallel supply is from the periosteum and extraosseous tissues. In Group 3, cortical flow was not significantly reduced, which demonstrates recruitment of this periosteal and extraosseous supply. These results lend support to the hypothesis that the blood supply to the healing diaphysis is principally from the periosteum and extraosseous tissues during the early peak period of blood flow.

The effect of cast immobilization on blood flow to the tibial diaphysis was studied by the microsphere method, both before and after casting of one hindlimb of adult New Zealand White rabbits. Preliminary studies were undertaken to investigate the possibility of the reduction of tibial flow by the microspheres used for the control measurements of blood flow. There were no significant differences in the flows to the tibial diaphysis or skeletal muscle between the immobilized and control limbs after either 1 or 2 weeks. This similarity between control and experimental limbs indicates that immobilization had no major effect on tibial blood flow over and above the systemic effects of the procedure.