University of Virginia, Center for Applied Biomechanics, 4040 Lewis & Clark Drive, Charlottesville 22911, VA, USA.
Universitat Politècnica de Catalunya-Barcelona Tech, Comte d'Urgell 187, CP 08036 Barcelona, Spain.
J Mech Behav Biomed Mater. 2014 May;33:99-108. doi: 10.1016/j.jmbbm.2013.04.027. Epub 2013 Jul 29.
The goal of this study was to determine material properties for the anterior cortex and subcortical regions of human patellae and relate those properties to mineral density and fractal dimension of the bone. Ten human patellae were obtained from eight fresh frozen human cadavers and subjected to anteriorly-directed spherical indentation-relaxation experiments using two different sized indenters to two different indentation depths. Response data were fit to a three-mode viscoelastic model obtained through elastic-viscoelastic correspondence of the Hertzian contact relation for spherical indentation. A location-specific effective bone density measurement that more heavily weighted bone material close to the indentation site (by von Mises stress distribution) was determined from micro-computed tomography (38µm resolution) data captured for each specimen. The same imagery data were used to compute location specific fractal dimension estimates for each indentation site. Individual and averaged patella material models verified the hypothesis that when the larger indenter and greater indentation depth is used to engage the surface and deeper (trabecular) bone, the bone exhibits a more compliant response than when only the surface (cortical) bone was engaged (instantaneous elastic modulus was 325MPa vs. 207MPa, p<0.05). Effective bone mineral density was shown to be a significant predictor of the elastic modulus for both small and large indentation types (p<0.05) despite relatively low correlations. Exponential regressions of fractal dimension on elastic modulus showed significant relationships with high correlation for both the small (R(2)=0.93) and large (R(2)=0.97) indentations.
本研究旨在确定人髌骨前皮质区和皮质下区域的材料特性，并将这些特性与骨的矿物质密度和分形维数相关联。从 8 具新鲜冷冻的人体尸体中获得了 10 个人髌骨，并使用两个不同尺寸的压头在两个不同的压入深度对其进行了向前的球形压痕-松弛实验。通过赫兹球形压痕接触关系的弹性-粘弹性对应关系，将响应数据拟合到三模态粘弹性模型。从为每个标本捕获的微计算机断层扫描（38µm 分辨率）数据中确定了一种位置特异性的有效骨密度测量值，该值更侧重于靠近压痕部位的骨材料（通过 von Mises 应力分布）。相同的图像数据用于计算每个压痕部位的位置特异性分形维数估计值。个体和平均髌骨材料模型验证了这样一个假设，即当较大的压头和较大的压入深度用于接触表面和更深的（小梁）骨时，与仅接触表面（皮质）骨时相比，骨表现出更具弹性的响应（瞬时弹性模量为 325MPa 对 207MPa，p<0.05）。尽管相关性相对较低，但有效骨矿物质密度被证明是小和大压入类型弹性模量的重要预测因子（p<0.05）。分形维数对弹性模量的指数回归显示出与小（R(2)=0.93）和大（R(2)=0.97）压痕均具有显著关系和高相关性。
