Investigation On Morphological And Mechanical Properties Of Mouse Tibia During Bone Remodeling

Osteoporosis is one of the most common bone diseases and has become a major health problem worldwide.However,the mechanism of bone remodeling induced by osteoporosis is still not fully understood.As estrogen defect is a major reason for osteoporosis,how it affects bone remodeling in spatio-temporal scope is still not clear.Parathyroid Hormone(PTH)is an effective bone anabolic drug which has been approved by FDA,but its use and mechanism are still under intense investigations.The main aim of this study is to investigate the effect of ovariectomy(Ovx)and PTH on the bone remodeling.This study uses animal experiments to create osteoporotic bone models and treated bone models which are completed in the University of Sheffiled: Thirteen C57Bl/6 female mice are ovariectomized(Ovx,n=6)or sham-operated(Sham,n=7).Ten C57BL/6J female mice are in control group(Wild,n=5)or in intervention group treated with PTH(WildPTH,n=5).The bone remodeling of the entire right tibia is monitored with the in vivo mirco computed tomography(?CT)(with a nominal voxel size of 10.4 ?m)at the mouse age of 14,16,17,18,19,20,21 and 22 weeks.Three bone morphological parameters(bone mineral content(BMC),bone volume(BV)and bone cross-sectional area)are calculated from the ?CT data base.The finite element(FE)models of the tibias are converted from the ?CT images by Matlab.Three bone mechanical parameters(strain energy density(SED),failure load and stiffness)are calculated in FE models.Besides the global changes of the entire tibia following the timeline,we apply a novel 4-dimensional approach developed in a previous study to monitor local changes in the whole tibia of female C57Bl/6 mice in 4 groups.According to the results of the global changes,Ovx has little influence on the total BMC and the total BV,but Ovx slightly reduces the tibial failure load and stiffness;PTH treatment increases total BMC,total BV,failure load and stiffness significantly.According to the results of local changes,Ovx reduces BMC and BV in the proximal tibia,which leads to the increase of SED there;PTH treatment improves BMC and BV in all partitions of the tibia,which leads to the decrease of SED everywhere.In addition,it is found Ovx significantly increases tibial endosteal area,whereas the changes of tibial periosteal area are not obvious;PTH promotes the expansion of periosteal area and the shrinking of endosteal area,especially in Lateral and Anterior parts.Through the spatio-temporal quantity analysis and FE analysis,this study reveals the mechanism how Ovx and PTH affect bone remodeling,which provides important theoretical basis for the investigation and treatment of osteoporosis.