Nyman Jeffry S, Uppuganti Sasidhar, Makowski Alexander J, Rowland Barbara J, Merkel Alyssa R, Sterling Julie A, Bredbenner Todd L, Perrien Daniel S
Department of Veterans Affairs, Tennessee Valley Healthcare System , Nashville, TN, USA ; Department of Orthopaedic Surgery and Rehabilitation, Vanderbilt University, Medical Center East , Nashville, TN, USA ; Department of Biomedical Engineering, Vanderbilt University Medical Center , Nashville, TN, USA ; Center for Bone Biology, Vanderbilt University Medical Center , Nashville, TN, USA.
Department of Orthopaedic Surgery and Rehabilitation, Vanderbilt University, Medical Center East , Nashville, TN, USA.
Bonekey Rep. 2015 Apr 22;4:664. doi: 10.1038/bonekey.2015.31. eCollection 2015.
As in clinical studies, finite element analysis (FEA) developed from computed tomography (CT) images of bones are useful in pre-clinical rodent studies assessing treatment effects on vertebral body (VB) strength. Since strength predictions from microCT-derived FEAs (μFEA) have not been validated against experimental measurements of mouse VB strength, a parametric analysis exploring material and failure definitions was performed to determine whether elastic μFEAs with linear failure criteria could reasonably assess VB strength in two studies, treatment and genetic, with differences in bone volume fraction between the control and the experimental groups. VBs were scanned with a 12-μm voxel size, and voxels were directly converted to 8-node, hexahedral elements. The coefficient of determination or R (2) between predicted VB strength and experimental VB strength, as determined from compression tests, was 62.3% for the treatment study and 85.3% for the genetic study when using a homogenous tissue modulus (E t) of 18 GPa for all elements, a failure volume of 2%, and an equivalent failure strain of 0.007. The difference between prediction and measurement (that is, error) increased when lowering the failure volume to 0.1% or increasing it to 4%. Using inhomogeneous tissue density-specific moduli improved the R (2) between predicted and experimental strength when compared with uniform E t=18 GPa. Also, the optimum failure volume is higher for the inhomogeneous than for the homogeneous material definition. Regardless of model assumptions, μFEA can assess differences in murine VB strength between experimental groups when the expected difference in strength is at least 20%.
与临床研究一样，基于骨骼计算机断层扫描（CT）图像开展的有限元分析（FEA），在评估对椎体（VB）强度的治疗效果的临床前啮齿动物研究中很有用。由于源自显微CT的有限元分析（μFEA）对小鼠椎体强度的预测尚未通过实验测量进行验证，因此进行了一项参数分析，探索材料和失效定义，以确定在两项研究（治疗和基因研究）中，控制组和实验组之间骨体积分数存在差异的情况下，具有线性失效标准的弹性μFEA是否能够合理评估椎体强度。椎体以12μm的体素大小进行扫描，体素直接转换为8节点六面体单元。当对所有单元使用18GPa的均匀组织模量（Et）、2%的失效体积和0.007的等效失效应变时，治疗研究中预测的椎体强度与通过压缩试验确定的实验椎体强度之间的决定系数或R²为62.3%，基因研究中为85.3%。当将失效体积降低到0.1%或增加到4%时，预测值与测量值之间的差异（即误差）会增加。与均匀的Et = 18GPa相比，使用不均匀的组织密度特定模量提高了预测强度与实验强度之间的R²。此外，不均匀材料定义的最佳失效体积高于均匀材料定义。无论模型假设如何，当预期强度差异至少为20%时，μFEA可以评估实验组之间小鼠椎体强度的差异。
