Section of Biomechanics, Bone and Joint Center, Henry Ford Hospital, 2799 West Grand Boulevard, Detroit, MI 48202, USA.
Bone. 2011 Oct;49(4):886-94. doi: 10.1016/j.bone.2011.07.006. Epub 2011 Jul 19.
Cancellous bone microstructure is an important determinant of the mechanical integrity of vertebrae. The numerous microstructural parameters that have been studied extensively are generally represented as a single value obtained as an average over a sample. The range of the intra-sample variability of cancellous microstructure and its effect on the mechanical properties of bone are less well-understood. The objectives of this study were to investigate the extent to which human cancellous bone microstructure within a vertebra i) is related to bone modulus and stress distribution properties and ii) changes along with age, gender and locations thoracic 12 (T12) vs lumbar 1 (L1). Vertebrae were collected from 15 male (66±15 years) and 25 female (54±16 years) cadavers. Three dimensional finite element models were constructed using microcomputed tomography images of cylindrical specimens. Linear finite element models were used to estimate apparent modulus and stress in the cylinders during uniaxial compression. The intra-specimen mean, standard deviation (SD) and coefficient of variation (CV) of microstructural variables were calculated. Mixed model statistical analysis of the results demonstrated that increases in the intra-specimen variability of the microstructure contribute to increases in the variability of trabecular stresses and decreases in bone stiffness. These effects were independent from the contribution from intra-specimen average of the microstructure. Further, the effects of microstructural variability on bone stiffness and stress variability were not accounted for by connectivity and anisotropy. Microstructural variability properties (SD, CV) generally increased with age, were greater in females than in males and in T12 than in L1. Significant interactions were found between age, gender, vertebra and race. These interactions suggest that microstructural variability properties varied with age differently between genders, races and vertebral levels. The current results collectively demonstrate that microstructural variability has a significant effect on mechanical properties and tissue stress of human vertebral cancellous bone. Considering microstructural variability could improve the understanding of bone fragility and improve assessment of vertebral fracture risk.
松质骨微观结构是决定椎体机械完整性的重要因素。大量广泛研究的微观结构参数通常表示为通过对样本进行平均得到的单一值。松质骨微观结构的样本内变异性范围及其对骨骼机械性能的影响尚未得到充分理解。本研究的目的是探讨以下两个问题：（i）在椎体中，人类松质骨微观结构在多大程度上与骨模量和应力分布特性相关；（ii）它随年龄、性别和部位（胸椎 12 与腰椎 1）的变化情况。从 15 名男性（66±15 岁）和 25 名女性（54±16 岁）尸体中采集了椎体。使用圆柱形样本的微计算机断层扫描图像构建了三维有限元模型。线性有限元模型用于估计圆柱体在单轴压缩过程中的表观模量和应力。计算了微观结构变量的样本内平均值、标准差（SD）和变异系数（CV）。对结果进行混合模型统计分析表明，微观结构变异性的增加会导致小梁应力的变异性增加，而骨刚度降低。这些效应独立于微观结构的样本内平均值。此外，微观结构变异性对骨刚度和应力变异性的影响不受连通性和各向异性的影响。微观结构变异性特性（SD、CV）通常随年龄增加而增加，女性大于男性，胸椎 12 大于腰椎 1。年龄、性别、椎体和种族之间存在显著的相互作用。这些相互作用表明，微观结构变异性特性在不同性别、种族和椎体水平之间随年龄的变化不同。这些结果共同表明，微观结构变异性对人类椎体松质骨的力学性能和组织应力有显著影响。考虑微观结构变异性可以提高对骨脆弱性的理解，并改善对椎体骨折风险的评估。
