Nyman Jeffry S, Roy Anuradha, Tyler Jerrod H, Acuna Rae L, Gayle Heather J, Wang Xiaodu
Department of Mechanical Engineering and Biomechanics, The University of Texas at San Antonio, San Antonio, Texas 78249, USA.
J Orthop Res. 2007 May;25(5):646-55. doi: 10.1002/jor.20337.
The risk of bone fracture depends in part on tissue quality, not just the size and mass. This study assessed the postyield energy dissipation of cortical bone in tension as a function of age and composition. Specimens were prepared from tibiae of human cadavers in which male and female donors were divided into two age groups: middle aged (51 to 56 years, n = 9) and elderly (72 to 90 years, n = 8). By loading, unloading, and reloading a specimen with rest periods inserted in between, tensile properties at incremental strain levels were assessed. In addition, postyield toughness was estimated and partitioned as plastic strain energy related to permanent deformation, released elastic strain energy related to stiffness loss, and hysteresis energy related to viscous behavior. Porosity, mineral and collagen content, and collagen crosslinks of each specimen were also measured to determine the micro- and ultrastructural properties of the tissue. Age affected all the energy terms plus strength but not elastic stiffness. The postyield energy terms were correlated with porosity, pentosidine (a marker of nonenzymatic crosslinks), and collagen content, all of which varied significantly with age. General linear models suggested that pentosidine concentration and collagen content provided the best explanation of the age-related decrease in the postyield energy dissipation. Among them, pentosidine concentration had the greatest contribution to plastic strain energy and was the best explanatory variable of damage accumulation.
骨折风险部分取决于组织质量，而非仅仅取决于尺寸和质量。本研究评估了皮质骨在拉伸时屈服后能量耗散随年龄和成分的变化情况。标本取自人类尸体的胫骨，其中男性和女性捐赠者被分为两个年龄组：中年组（51至56岁，n = 9）和老年组（72至90岁，n = 8）。通过对标本进行加载、卸载，并在其间插入休息期后重新加载，评估了不同应变水平下的拉伸性能。此外，还估算了屈服后韧性，并将其划分为与永久变形相关的塑性应变能、与刚度损失相关的释放弹性应变能以及与粘性行为相关的滞后能。还测量了每个标本的孔隙率、矿物质和胶原蛋白含量以及胶原蛋白交联情况，以确定组织的微观和超微结构特性。年龄影响了所有能量项以及强度，但不影响弹性刚度。屈服后能量项与孔隙率、戊糖苷（非酶交联的标志物）和胶原蛋白含量相关，所有这些均随年龄显著变化。一般线性模型表明，戊糖苷浓度和胶原蛋白含量最能解释屈服后能量耗散随年龄的下降情况。其中，戊糖苷浓度对塑性应变能的贡献最大，是损伤累积的最佳解释变量。
