Previous studies have not quantified the relative contributions of intracortical and extracortical perfusion to cortical porosity and new bone formation. The current study was performed to determine the relative importance of intramedullary, intracortical, and extraosseous soft-tissue blood flow and type of tissue to the repair of devascularized canine tibial cortex. A 2.5-cm segment of tibia between two standardized osteotomies was devascularized. The segment was replaced anatomically and stabilized with a plate. The animals were divided randomly into two groups: skin coverage (N = 8) and muscle coverage (N = 8). Thirty-one days postoperatively, cerium141 microspheres were injected, prior to sacrifice, to measure blood flow. Extraosseous soft-tissue perfusion was the same in the skin coverage and muscle flap coverage groups. There was no relationship between intramedullary or extraosseous soft-tissue flow and depth of new bone formation and cortical porosity. Intracortical blood flow was directly related to depth of new bone formation (p = 0.0006) and cortical porosity (outer cortex, p = 0.001; inner cortex, p = 0.0001). These findings indicate that the cortical repair process is linked to the restoration of perfusion and that muscle coverage, rather than the quantity of blood flow, determines the extent of cortical repair.