Age-related changes in the 3 D hierarchical structure of rat tibia cortical bone 2 characterized by high resolution micro-CT 3

Three-dimensional hierarchical structure of female Sprague-Dawley rat tibia cortical 11 bone was characterized as a function of age (3, 12, 32, 42, 60, and 72 weeks) using a high 12 resolution micro-computed tomography. At the whole bone level, 3 week samples exhibited 13 statistically significant differences in a mean total tissue volume, mean cortical bone volume, 14 mean cortical bone volume density, mean periosteal perimeter, and mean cortical thickness (p < 15 0.05) compared to all other ages. At the tissue level, there was a statistically significant increase 16 in a mean canal number density and a decrease in a mean canal volume and diameter between 3 17 week and 12 week samples. While no significant variations were found between mean canal 18 lengths, there was a dependence of mean canal orientation on age. At the cell level, there were no 19 statistically significant differences in a lacuna number density and a lacuna volume density, and 20 all lacunae element-based parameters displayed no dependence on age across age. In addition, at 21 the microstructural level, the cannular indices were reported separately for anterior, posterior, 22 medial, lateral anatomical regions. From 3 32 weeks of age, there existed significantly less 23 Articles in PresS. J Appl Physiol (January 17, 2013). doi:10.1152/japplphysiol.00948.2011