Bone Abstracts

This study was undertaken to evaluate the effect of whole-body vibration (WBV) with extremely low-amplitude on early-stage bone healing. Experiments were conducted with an approval of the Animal Research Committee of Osaka University Graduate School of Engineering Science. Male BALB/cByJJcl mice were subjected to a 0.5 mm drill-hole surgery on a tibial diaphysis at 14 weeks of age and divided into three groups (n=8 each) from the day after the surgery, which received 0.03 g WBV at either 30 Hz (W30), 90 Hz (W90), or 0 Hz, i.e. sham WBV (SW) for 20 min/day respectively. After 12-day WBV, each animal was perfused with agarose solution containing zirconia nanoparticles for vascular casting. Following euthanasia, the defect portion was harvested, fixed with 4% paraformaldehyde solution, and scanned by synchrotron light at 17.9 and 18.1 keV, below and above the zirconia k-edge respectively. The two scan data sets were reconstructed, and vascular and bone images (2.7 μm voxel resolution) were obtained through image subtraction. K₂HPO₄ phantom solutions were also scanned for bone mineral quantification. Between-group differences in volume fractions of newly formed bone (B.Vf) and angiogenic vessels (V.Vf) as well as the mean degree of mineralization (DM) in the defect were tested for significance (P<0.05) with the Kruskal–Wallis test followed by Dunn’s multiple comparison test. B.Vf was higher in W30 (52±1%) than in SW (41±4%) while V.Vf was lower in W30 (4±2%) than in SW (10±4%). DM was higher in W30 (0.79±0.02 g/cm³) than in SW (0.76±0.03 g/cm³). B.Vf (45±2%) and DM (0.78±0.02 g/cm³) in W90 tended to be higher than those in SW. These results suggest that WBV with extremely low-amplitude facilitates early-stage bone defect repair. Reduced angiogenesis, which could still suffice to promote osteogenesis, implies that the present WBV drives the differentiation of mesenchymal stem cells preferentially toward bone-forming cells rather than endothelial cells.