Institute of Orthopaedic Research and Biomechanics, Ulm University, Helmholtzstrasse 14, D-89081 Ulm, Germany.
J Biomech. 2010 Jun 18;43(9):1731-7. doi: 10.1016/j.jbiomech.2010.02.026. Epub 2010 Mar 5.
Osteoporosis-related vertebral fractures represent a major public health problem. Anatomy-specific CT-based finite element (FE) simulations could help in identifying which vertebrae have the highest risk of fracture and thus help to decide upon the need for vertebroplasty or other surgical intervention. Continuum level FE simulations require effective macroscopic material properties of the vertebra. Micro finite element (microFE) models can be used to circumvent the difficult experiments that are necessary to determine these effective properties. From a quantitative point of view, these microFE models depend critically on the chosen trabecular tissue properties. The question remains whether linear elastic microFE models of vertebral trabecular bone with and without specimen-specific tissue properties yield similar results as non-destructive macroscopic experiments under moist conditions. microFE models were set up from microCT scans with specimen-specific or average tissue moduli measured by nanoindentation under dry and wet testing conditions. Non-destructive macroscopic mechanical compression, tension and torsion tests were performed. Experimentally obtained and simulated apparent stiffnesses were compared. No significant difference was found when comparing microFE simulations with wet tissue properties and experiments for tension, compression and torsion (p>0.05). Concordance correlation coefficients were high for tension and compression (r(c)(wet)>or=0.96,p<0.05) but moderate for torsion (r(c)(wet)=0.81,p<0.05). The agreement between simulation and experiment was confirmed by Bland-Altman plots which showed mean differences <or=10MPa. Surprisingly, the agreement between simulation and experiment was not reduced by using an average tissue modulus. The results indicate that valid microFE models can be set up using average tissue properties obtained under wet indentation conditions.
骨质疏松性椎体骨折是一个主要的公共卫生问题。基于解剖结构的 CT 有限元（FE）模拟可以帮助确定哪些椎体骨折风险最高，从而有助于决定是否需要进行椎体成形术或其他手术干预。连续体水平的 FE 模拟需要有效的椎体宏观材料性能。微有限元（microFE）模型可用于避免确定这些有效特性所需的困难实验。从定量的角度来看，这些 microFE 模型严重依赖于所选的小梁组织特性。问题仍然是，在潮湿条件下，具有和不具有特定于标本的组织特性的线性弹性 microFE 模型是否会产生与无损宏观实验相似的结果。microFE 模型是根据具有特定于标本或平均组织模量的 microCT 扫描建立的，这些组织模量是通过在干燥和潮湿测试条件下的纳米压痕测量得到的。进行了无损宏观机械压缩、拉伸和扭转测试。比较了实验获得的和模拟的表观刚度。在拉伸、压缩和扭转方面，当比较具有湿组织特性的 microFE 模拟和实验时，没有发现显著差异（p>0.05）。对于拉伸和压缩，一致性相关系数较高（r(c)(wet)>或=0.96，p<0.05），但对于扭转，一致性相关系数中等（r(c)(wet)=0.81，p<0.05）。模拟与实验之间的一致性通过 Bland-Altman 图得到了确认，该图显示平均差异<或=10MPa。令人惊讶的是，使用平均组织模量并没有降低模拟与实验之间的一致性。结果表明，可以使用在湿压痕条件下获得的平均组织特性来建立有效的 microFE 模型。
