Three-Dimensional Cortical Bone Microstructure in a Rat Model of Hypoxia-Induced Growth Retardation

Abstract

Little is known about hypoxia-induced modification of the canal network in the cortical bone despite its involvement in intracortical vascularity and bone blood supply. In this study, we examined the effect of chronic hypoxia on the canal network in postnatal bone. Tibiae were harvested from 4- and 8-week-old rats (hyp-4 and -8, n = 8 each), whose growth was retarded owing to postnatal exposure to hypoxia (12-14% O₂), and from 3- and 4-week-old normoxic rats (cnt-4 and -5, n = 8 each), which were similar in tibial length and cortical cross-sectional area to hyp-4 and -8, respectively. The diaphyseal canals were detected by monochromatic synchrotron radiation CT with a 3.1-μm voxel resolution. The anatomical properties of the canal network were compared between age- or size-matched hypoxic and normoxic groups. The canals were larger in diameter, were more densely distributed and connected, and opened into the marrow cavity with a higher density in hyp-4 than in cnt-4. The canal density and connectivity were also higher in hyp-4 than in cnt-3. The canal diameter, density, and connectivity were smaller in hyp-8 than in cnt-4; however, the densities of endocortical and periosteal canal openings did not differ between hyp-8 and cnt-4. We concluded that chronic hypoxia enhanced the formation of cortical canal networks at the postnatal developmental stage, probably facilitating intra- and transcortical vascularization and bone perfusion accordingly.

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

“…Particularly, Schneider et al (46) found a significant difference between the anterior and posterior regions, citing a fourfold decrease in the canal volume density and a fivefold decrease in the canal number density in the posterior region compared with the anterior region. An analogous site dependency was found by Matsumoto et al (31) in rat tibiae harvested from 3-and 4-wk-old rats. Using monochromatic synchrotron radiation CT (SRCT), Matsumoto and colleagues found the posterior region of the tibia to be less porous than the anterior region.…”

“…Schneider et al (46) also observed a site dependence of mean canal orientation within mouse femora, although those findings found the anterior and medial regions to contain canals with a greater mean orientation. These differences in the spatial orientation of canals may be due to possible differences in a nonuniform load distribution in the tibia (31,49) in these two species.…”

“…However, much less has been done applying this technology to the assessment of the cortical microstructure of small rodents. Due to the smaller scale of the vascular canal network of these animals, the analysis of rat and mouse cortical bone has been mainly achieved through the use of synchrotron radiation micro-CT (SRCT) (31,32,46,53). The use of SRCT offers many advantages over conventional desktop micro-CT imaging including higher spatial resolution and the elimination of beam-hardening artifacts (8,16), allowing for the determination of local bone mineralization (41,50).…”

Subtraction micro-computed tomography of angiogenesis and osteogenesis during bone repair using synchrotron radiation with a novel contrast agent

“…The high detection sensitivity and quantitative performance of this type of imaging have been reported in angiography and lung imaging using iodine and xenon, respectively, as contrast agents. 28,29 Here, we focused on the zirconium dioxide k-edge that is close to the energy suitable for mCT imaging of rodent cortical bone 22,30 and developed ZrCA for sSRCT, which provides several advantages in bone microvascular imaging.…”

“…For rat tibial bone imaging at SPring-8, the 20-keV X-ray yielded good contrast with a high signal-to-noise ratio, allowing quantitative evaluation of its cortical microstructure and mineralization. 22,30 The zirconium dioxide k-edge (18 keV) is not far from 20 keV, and the light brilliance is as extremely high at 18 keV as at 20 keV in SPring-8 (http://www.spring8.or.jp/en/about_us/ whats_sr/sp8_features/). Thus, the X-ray energy close to 18 keV is ideal for not only separately imaging of vascular and bone microstructures of small or rodent bone specimen but also assessment of its mineral density, which shows regionto-region and time-to-time variations during bone repair.…”