Bone Abstracts

Mechanical stress and strain generated by physical exercises or the other passive stimulations are well known to have a positive effect on the growing musculoskeletal system. Especially, when the impact stimulation which evokes high magnitude of strain in a second is applied to bone, it improves bone qualities. Thus, to verify the effect of impact stimulation, we conducted longitudinal study on morphological properties of the tibia in growing rats. Free falls from designated heights were implemented to induce high impact stimulation. Six-week-old male Wistar rats were randomly allocated to one of three conditions: free fall from 20-cm-height (W20; n=7), free fall from 40-cm-height (W40; n=7), and control (WC; n=7). The impact stimulations were administered to the free fall groups, ten times/day, and 5 days/week for 8 weeks. The right tibia was scanned by in-vivo micro-CT at 0, 4, and 8 weeks of experiment and structural parameters and tibia`s length were measured to evaluate the variation in morphological characteristics and bone length with maturing. After 4 weeks of the experiment, relative values (value of 4 or 8 weeks/0 week, thus 1 at 0 week) of BV/TV and Tb.N were significantly higher in W40 group than in WC and W20 groups (all P<0.05), while relative values of Tb.Sp was significantly smaller (P<0.05). However, there were no difference in relative values in Tb.Th and bone length among the groups (all P>0.05). No significant difference in all structural parameters between W20 and WC groups (P>0.05). After 8 weeks of the experiments, relative values in Tb.Th and tibial length were significantly higher in W40 group than in WC and W20 groups (P<0.05). Only relative value of Tb.Sp in W20 group was significantly smaller than that in WC group (P<0.05). Overall, impact stimulation for 8 weeks generated by free falls at a 40-cm-height affected not only trabecular bone homeostasis but also bone growth. Furthermore, since a significant bone growth was appeared after 8 weeks of stimulation, but not after 4 weeks, continuous stimulation may be needed to improve bone growth length in growing rats.