Unnikrishnan Ginu U, Barest Glenn D, Berry David B, Hussein Amira I, Morgan Elise F
J Biomech Eng. 2013 Oct 1;135(10):101007-11. doi: 10.1115/1.4025179.
Intra- and inter-specimen variations in trabecular anisotropy are often ignored in quantitative computed tomography (QCT)-based finite element (FE) models of the vertebra. The material properties are typically estimated solely from local variations in bone mineral density (BMD), and a fixed representation of elastic anisotropy ("generic anisotropy") is assumed. This study evaluated the effect of incorporating specimen-specific, trabecular anisotropy on QCT-based FE predictions of vertebral stiffness and deformation patterns. Orthotropic material properties estimated from microcomputed tomography data ("specimen-specific anisotropy"), were assigned to a large, columnar region of the L1 centrum (n = 12), and generic-anisotropic material properties were assigned to the remainder of the vertebral body. Results were compared to FE analyses in which generic-anisotropic properties were used throughout. FE analyses were also performed on only the columnar regions. For the columnar regions, the axial stiffnesses obtained from the two categories of material properties were uncorrelated with each other (p = 0.604), and the distributions of minimum principal strain were distinctly different (p ≤ 0.022). In contrast, for the whole vertebral bodies in both axial and flexural loading, the stiffnesses obtained using the two categories of material properties were highly correlated (R2 > 0.82, p < 0.001) with, and were no different (p > 0.359) from, each other. Only moderate variations in strain distributions were observed between the two categories of material properties. The contrasting results for the columns versus vertebrae indicate a large contribution of the peripheral regions of the vertebral body to the mechanical behavior of this bone. In companion analyses on the effect of the degree of anisotropy (DA), the axial stiffnesses of the trabecular column (p < 0.001) and vertebra (p = 0.007) increased with increasing DA. These findings demonstrate the need for accurate modeling of the peripheral regions of the vertebral body in analyses of the mechanical behavior of the vertebra.
在基于定量计算机断层扫描（QCT）的椎体有限元（FE）模型中，小梁各向异性的标本内和标本间差异常常被忽视。材料属性通常仅根据骨矿物质密度（BMD）的局部变化来估计，并假定弹性各向异性的固定表示形式（“一般各向异性”）。本研究评估了纳入标本特异性小梁各向异性对基于QCT的椎体刚度和变形模式有限元预测的影响。从微观计算机断层扫描数据估计的正交各向异性材料属性（“标本特异性各向异性”）被分配到L1椎体的一个大的柱状区域（n = 12），一般各向异性材料属性被分配到椎体的其余部分。将结果与全程使用一般各向异性属性的有限元分析进行比较。还仅对柱状区域进行了有限元分析。对于柱状区域，从两类材料属性获得的轴向刚度彼此不相关（p = 0.604），最小主应变的分布明显不同（p≤0.022）。相比之下，对于轴向和弯曲加载的整个椎体，使用两类材料属性获得的刚度高度相关（R2>0.82，p<0.001），且彼此无差异（p>0.359）。在两类材料属性之间仅观察到应变分布的适度变化。柱状区域与椎体的对比结果表明椎体周边区域对该骨骼力学行为有很大贡献。在关于各向异性程度（DA）影响的配套分析中，小梁柱（p<0.001）和椎体（p = 0.007）的轴向刚度随DA增加而增加。这些发现表明，在分析椎体力学行为时，需要对椎体周边区域进行准确建模。
