Trabecular bone dynamics in mice subjected to unilateral sciatic neurectomy assessed by in vivo μCT using monochromatic synchrotron radiation

Abstract

Monochromatic synchrotron radiation μCT (SRCT) allows quantitative imaging of bone microstructure with high spatial resolutions. Using an SRCT system developed at Japan large‐scale synchrotron radiation facility (Spring‐8), we evaluated the structural changes of tibial metaphyseal trabecular network in ICR mice (n=6) subjected to unloading in one hindlimb induced by sciatic neurectomy at 13 weeks of age. Both hindlimbs were scanned for five minutes at 10 days and 20 days after surgery. The three‐dimensional image was reconstructed with a two‐dimensional filtered backward projection algorithm based on radiographic images acquired with 25‐keV X‐ray over an angular range of 0°–180° with 0.2° steps, providing contiguous images comprised of 1000 × 1000 cubic voxels of 11.7 μm in size. Two reconstructed images at the two different time points were matched by a registration method based on maximizing mutual information. After bone segmentation by setting a threshold value to the hydroxyapatite density of 0.82 g/cm3, local trabecular resorption and formation were quantitated and compared between intact (INT) and sciatic‐neurectomized (SN) hindlimbs. Mechanical unloading reduces the rate of trabecular bone formation but has no effect on the rate of bone resorption as shown in the figure. In both hindlimbs, the number densities of segments and nodes in the trabecular network decreased whereas the trabecular bone thickeness increased, possibly in compensation for the regression of trabecular network. However, the increase of trabecular thickness decreased by 13% in SN hindlimbs.