The disuse effect on canal network structure and oxygen supply in the cortical bones of rats

In this study, based on the measurements of intracortical vascular canal structure, we investigated the disuse effect on local O-2 supply in the cortical bones of growing rats. Hindlimb disuse was produced by unilateral sciatic neurectomy (SN) at 4weeks age. The canal network structures within tibial cortical bone were evaluated in 8- and 12-week-old rats undergoing SN or no treatment (control) by synchrotron radiation micro-CT. Additionally, we developed an intracortical network model by combining the imaged-based canal network with a bone matrix containing theoretical lacunar-canalicular network, and determined the distribution of O-2 concentration in bone tissue numerically. In the control bone, canal network was reduced with growth, resulting in decreased blood flow and averaged O-2 concentration and increased spatial heterogeneity in tissue O-2 concentration. Disuse reduced the canal network, leading to a lower flow rate, lower average O-2 concentration and higher heterogeneity of O-2 concentrations. However, the rarefaction of the canal network with growth was smaller under the disuse condition, and accordingly, the flow rate, the average O-2 concentration and the heterogeneity of O-2 concentrations remained stable. In particular, although the fraction of the canal volume was smaller, the densities of canal segments and bifurcation points under disuse condition tended to be higher than those of the control bone. The heterogeneity of O-2 concentration was lower. Our results indicated that the disuse may lead to more uniformity in the canal network structure and thereby uniform O-2, possibly contributing to O-2 supply efficiency.