Orthopaedic Biomechanics Laboratory, Department of Mechanical Engineering, University of California, Berkeley, CA CA 94720-1740, USA.
Bone. 2010 Apr;46(4):1162-9. doi: 10.1016/j.bone.2009.12.009. Epub 2009 Dec 23.
The intra-specimen spatial variation in mineralization of bone tissue can be changed by drug treatments that alter bone remodeling. However, the contribution of such changes to the overall biomechanical effect of a treatment on bone strength is not known. To provide insight into this issue, we used a rat model to determine the effects of ovariectomy, parathyroid hormone, and raloxifene (vs. sham) on the contribution of spatial variations in mineralization to treatment-induced changes in vertebral stiffness. Mineral density was measured from 6-microm voxel-sized quantitative micro-CT scans. Whole-vertebral and trabecular stiffness values were estimated using finite element analysis of these micro-CT scans, first including all intra-specimen variations in mineral density in the model and then excluding such variations by using a specimen-specific average density throughout each specimen. As expected, we found appreciable effects of treatment on overall bone stiffness, the effect being greater for the trabecular compartment (up to 52% reduction vs. sham, p<0.0001) than the whole vertebra (p=0.055). Intra-specimen mean mineralization was not changed with treatment but the intra-specimen variation in mineralization was, although the effect was small (4%). Intra-specimen spatial variations in mineralization accounted for 10-12% and 5-6% of overall stiffness of the trabecular compartment and whole vertebral body, respectively. However, after accounting for all treatment effects on bone geometry and trabecular microstructure, any treatment effects due to changes in mineralization were negligible (<2%), although statistically detectable (p<0.02). We conclude that, despite a role in the general biomechanical behavior of bone, the spatial variations in tissue mineralization, as measured by quantitative micro-CT, did not appreciably contribute to ovariectomy-, PTH-, or raloxifene-induced changes in stiffness of the whole bone or the trabecular compartment in these rat vertebrae.
骨组织矿化的标本内空间变化可因改变骨重建的药物治疗而改变。然而，这种变化对治疗后骨强度的整体生物力学效应的贡献尚不清楚。为了深入了解这个问题，我们使用大鼠模型来确定卵巢切除术、甲状旁腺激素和雷洛昔芬（与假手术相比）对骨刚度治疗引起的变化中矿化空间变化的贡献。使用 6 微米体素大小的定量微 CT 扫描测量矿物质密度。使用这些微 CT 扫描的有限元分析来估计整个椎体和小梁的刚度值，首先在模型中包含所有标本内矿物质密度的变化，然后通过在每个标本中使用特定标本的平均密度来排除这种变化。正如预期的那样，我们发现治疗对整体骨刚度有明显的影响，这种影响在小梁隔（与假手术相比，降低 52%，p<0.0001）比整个椎体（p=0.055）更明显。标本内平均矿化没有因治疗而改变，但矿化的标本内变化是存在的，尽管影响很小（4%）。标本内矿化的空间变化分别占小梁隔和整个椎体刚度的 10-12%和 5-6%。然而，在考虑到所有治疗对骨几何形状和小梁微结构的影响后，由于矿化变化引起的任何治疗效果都可以忽略不计（<2%），尽管在统计学上是可检测的（p<0.02）。我们得出结论，尽管组织矿化的空间变化在骨的一般生物力学行为中起作用，但通过定量微 CT 测量，它并没有显著影响卵巢切除术、PTH 或雷洛昔芬引起的整个骨或小梁隔刚度的变化。
