Arts et Metiers Paris Tech, Bd de l'Hôpital, Paris, France.
Spine (Phila Pa 1976). 2012 Feb 1;37(3):E156-62. doi: 10.1097/BRS.0b013e3182293628.
A finite element analysis on osteoporotic vertebrae.
This study aims to validate subject-specific finite element models (FEMs) derived from a low-dose imaging system (EOS, Biospace Med, France) for the prediction of vertebral strength. The vertebrae are submitted to an eccentric compression force leading to compression and anterior bending.
Given the aging population, osteoporosis and vertebral fractures are a major public health issue. A low bone mineral density (BMD) does not always explain incident fractures, and multifactorial analyses are required. In this context, FEMs based on quantitative computed tomography (QCT) have been proposed to predict vertebral strength in vitro or quantify effects of treatments. However, the clinical use of such a model for the in vivo follow-up of the whole spine is limited by the high-radiation dose induced by QCT and the lying position, which does not allow postural assessment with the same modality.
Fourteen vertebrae were modeled using a parametric meshing method. The mesh was subject-specific using geometric parameters computed on the 3-dimensional (3D) reconstructions obtained from the EOS biplanar radiographs. The contribution of cortical bone was taken into account by modeling a cortico-cancellous shell whose properties were derived from experimental data. The effect of subject-specific bone Young's moduli derived from EOS vertebral areal BMD was quantified. The 3D position of the point-of-load application and the 3D orientation of the force was faithfully reproduced in the model to compare the predicted strength and experimental strength under the same loading conditions.
The relative error of prediction decreased from 43% to 16% (2.5 times) when subject-specific mechanical properties, derived from EOS areal BMD, were implemented in the FEM compared with averaged material properties. The resulting subject-specific FEMs predicted vertebral strength with a level of significance close to the QCT-based models (r adjusted = 0.79, root mean square error = 367 N).
This work underlines the potential of low-dose biplanar x-ray devices to make subject-specific FEMs for prediction of vertebral strength.
骨质疏松椎体的有限元分析。
本研究旨在验证源自低剂量成像系统（EOS，Biospace Med，法国）的特定于个体的有限元模型（FEM），以预测椎体强度。椎体受到偏心压缩力，导致压缩和前弯。
随着人口老龄化，骨质疏松症和椎体骨折是一个主要的公共卫生问题。低骨密度（BMD）并不总是解释骨折事件，需要进行多因素分析。在这种情况下，已经提出了基于定量计算机断层扫描（QCT）的 FEM 来预测体外椎体强度或量化治疗效果。然而，由于 QCT 引起的高辐射剂量以及仰卧位限制了相同模态的姿势评估，因此该模型在整个脊柱的临床随访中应用有限。
使用参数化网格方法对 14 个椎体进行建模。网格是特定于个体的，使用从 EOS 双平面射线照片获得的 3D 重建中计算的几何参数。通过建模皮质-松质壳来考虑皮质骨的贡献，其特性源自实验数据。定量了源自 EOS 椎体面积 BMD 的特定于个体的骨杨氏模量的影响。在模型中忠实地再现了加载点的 3D 位置和力的 3D 方向，以便在相同的加载条件下比较预测强度和实验强度。
与平均材料特性相比，当将源自 EOS 面积 BMD 的特定于个体的机械特性实施到 FEM 中时，预测的相对误差从 43%降低到 16%（提高了 2.5 倍）。由此产生的特定于个体的 FEM 以接近基于 QCT 的模型的显着水平预测了椎体强度（调整后的 r = 0.79，均方根误差= 367 N）。
这项工作强调了低剂量双平面 X 射线设备用于制作预测椎体强度的特定于个体的 FEM 的潜力。
