Vennin S, Desyatova A, Turner J A, Watson P A, Lappe J M, Recker R R, Akhter M P
University of Nebraska-Lincoln, NE, United States.
Osteoporosis Research Center, Creighton University, Omaha, NE, United States.
Bone. 2017 Apr;97:233-242. doi: 10.1016/j.bone.2017.01.031. Epub 2017 Jan 27.
Osteoporotic (low-trauma) fractures are a significant public health problem. Over 50% of women over 50yrs. of age will suffer an osteoporotic fracture in their remaining lifetimes. While current therapies reduce skeletal fracture risk by maintaining or increasing bone density, additional information is needed that includes the intrinsic material strength properties of bone tissue to help develop better treatments, since measurements of bone density account for no more than ~50% of fracture risk. The hypothesis tested here is that postmenopausal women who have sustained osteoporotic fractures have reduced bone quality, as indicated with measures of intrinsic material properties compared to those who have not fractured. Transiliac biopsies (N=120) were collected from fracturing (N=60, Cases) and non-fracturing postmenopausal women (N=60, age- and BMD-matched Controls) to measure intrinsic material properties using the nano-indentation technique. Each biopsy specimen was embedded in epoxy resin and then ground, polished and used for the nano-indentation testing. After calibration, multiple indentations were made using quasi-static (hardness, modulus) and dynamic (storage and loss moduli) testing protocols. Multiple indentations allowed the median and variance to be computed for each type of measurement for each specimen. Cases were found to have significantly lower median values for cortical hardness and indentation modulus. In addition, cases showed significantly less within-specimen variability in cortical modulus, cortical hardness, cortical storage modulus and trabecular hardness, and more within-specimen variability in trabecular loss modulus. Multivariate modeling indicated the presence of significant independent mechanical effects of cortical loss modulus, along with variability of cortical storage modulus, cortical loss modulus, and trabecular hardness. These results suggest mechanical heterogeneity of bone tissue may contribute to fracture resistance. Although the magnitudes of differences in the intrinsic properties were not overwhelming, this is the first comprehensive study to investigate, and compare the intrinsic properties of bone tissue in fracturing and non-fracturing postmenopausal women.
骨质疏松性（低创伤）骨折是一个重大的公共卫生问题。50岁以上的女性中，超过50%会在余生遭受骨质疏松性骨折。虽然目前的治疗方法通过维持或增加骨密度来降低骨骼骨折风险，但还需要更多信息，包括骨组织的内在材料强度特性，以帮助开发更好的治疗方法，因为骨密度测量仅占骨折风险的约50%。这里所检验的假设是，与未发生骨折的绝经后女性相比，发生骨质疏松性骨折的绝经后女性骨质量降低，这可通过内在材料特性的测量来表明。从发生骨折的绝经后女性（N = 60，病例组）和未发生骨折的绝经后女性（N = 60，年龄和骨密度匹配的对照组）中采集了经髂骨活检样本（N = 120），使用纳米压痕技术测量其内在材料特性。每个活检样本被嵌入环氧树脂中，然后进行研磨、抛光并用于纳米压痕测试。校准后，使用准静态（硬度、模量）和动态（储能模量和损耗模量）测试方案进行多次压痕。多次压痕使得能够计算每个样本每种测量类型的中位数和方差。发现病例组的皮质硬度和压痕模量的中位数显著更低。此外，病例组在皮质模量、皮质硬度、皮质储能模量和小梁硬度方面的样本内变异性显著更小，而在小梁损耗模量方面的样本内变异性更大。多变量建模表明皮质损耗模量存在显著的独立力学效应，以及皮质储能模量、皮质损耗模量和小梁硬度的变异性。这些结果表明骨组织的力学异质性可能有助于抗骨折能力。尽管内在特性差异的幅度并不巨大，但这是第一项全面研究并比较发生骨折和未发生骨折的绝经后女性骨组织内在特性的研究。
