Structural pattern and functional correlations of the long bone diaphyses intracortical vascular system: investigation carried out with China ink perfusion and multiplanar analysis in the rabbit femur.

The intracortical vessel system of the rabbit femur has been studied after perfusion of the vascular tree with a water solution of dye (China ink) with multiplanar analysis. This method utilizes the full depth of field of the microscope objectives focusing different planes of the thick cortex. The microscopic observation even if restricted to a limited volume of cortex allowed to differentiate true 3-D nodes (54.5%) from the superimposition of vessels lying on different planes. The network model with elongated meshes preferentially oriented along the longitudinal axis of the diaphysis in his static configuration is not very different from the vascular anatomy depicted in the 2-D traditional models; however, the semi-quantitative morphometric analysis applied to the former supported the notion of a multidirectional microvascular network allowing change of flow according to the functional requirements. Other peculiar aspects not previously reported were cutting cone loops, blind-end and short-radius-bent vessels, and button-holes figures. The network design and node distribution were consistent with the straight trajectory of the secondary remodeling, with the proximal-to-distal and distal-to-proximal advancement directions of the cutting cones and with two main modes of node formation, namely bifurcation of the cutting cone and interception with pre-existing canals. The general organization of the network and its uninterrupted transformation during bone modeling and remodeling suggested a substantial plasticity of the intracortical vascular system capable to adapt itself to the changeable haemodynamic conditions.