Institute of Lightweight Design and Structural Biomechanics, Vienna University of Technology, Gußhausstrasse 27-29, 1040 Vienna, Austria.
Osteoporos Int. 2012 Feb;23(2):563-72. doi: 10.1007/s00198-011-1568-3. Epub 2011 Feb 23.
While dual energy X-ray absorptiometry (DXA) is considered the gold standard to evaluate fracture risk in vivo, in the present study, the quantitative computed tomography (QCT)-based finite element modeling has been found to provide a quantitative and significantly improved prediction of vertebral strength in vitro. This technique might be used in vivo considering however the much larger doses of radiation needed for QCT.
Vertebral fracture is a common medical problem in osteoporotic individuals. Bone mineral density (BMD) is the gold standard measure to evaluate fracture risk in vivo. QCT-based finite element (FE) modeling is an engineering method to predict vertebral strength. The aim of this study was to compare the ability of FE and clinical diagnostic tools to predict vertebral strength in vitro using an improved testing protocol.
Thirty-seven vertebral sections were scanned with QCT and high resolution peripheral QCT (HR-pQCT). Bone mineral content (BMC), total BMD (tBMD), areal BMD from lateral (aBMD-lat), and anterior-posterior (aBMD-ap) projections were evaluated for both resolutions. Wedge-shaped fractures were then induced in each specimen with a novel testing setup. Nonlinear homogenized FE models (hFE) and linear micro-FE (μFE) were generated from QCT and HR-pQCT images, respectively. For experiments and models, both structural properties (stiffness, ultimate load) and material properties (apparent modulus and strength) were computed and compared.
Both hFE and μFE models predicted material properties better than structural ones and predicted strength significantly better than aBMD computed from QCT and HR-pQCT (hFE: R² = 0.79, μFE: R² = 0.88, aBMD-ap: R² = 0.48-0.47, aBMD-lat: R² = 0.41-0.43). Moreover, the hFE provided reasonable quantitative estimations of the experimental mechanical properties without fitting the model parameters.
The QCT-based hFE method provides a quantitative and significantly improved prediction of vertebral strength in vitro when compared to simulated DXA. This superior predictive power needs to be verified for loading conditions that simulate even more the in vivo case for human vertebrae.
虽然双能 X 射线吸收法（DXA）被认为是评估体内骨折风险的金标准，但在本研究中，基于定量计算机断层扫描（QCT）的有限元建模已被发现可提供体外椎体强度的定量和显著改善的预测。然而，鉴于 QCT 需要更大剂量的辐射，该技术可能会在体内使用。
椎体骨折是骨质疏松个体中常见的医疗问题。骨密度（BMD）是评估体内骨折风险的金标准。基于 QCT 的有限元（FE）建模是一种预测椎体强度的工程方法。本研究的目的是使用改进的测试方案比较 FE 和临床诊断工具预测体外椎体强度的能力。
用 QCT 和高分辨率外周 QCT（HR-pQCT）扫描 37 个椎体段。评估两种分辨率的骨矿物质含量（BMC）、总 BMD（tBMD）、侧位（aBMD-lat）和前后位（aBMD-ap）的面积 BMD。然后，用一种新的测试装置在每个标本中诱导楔形骨折。从 QCT 和 HR-pQCT 图像分别生成非线性均质化 FE 模型（hFE）和线性微 FE（μFE）。对于实验和模型，均计算并比较了结构特性（刚度、极限载荷）和材料特性（表观模量和强度）。
hFE 和 μFE 模型均比结构模型更好地预测了材料特性，比从 QCT 和 HR-pQCT 计算的 aBMD 更好地预测了强度（hFE：R²=0.79，μFE：R²=0.88，aBMD-ap：R²=0.48-0.47，aBMD-lat：R²=0.41-0.43）。此外，hFE 无需拟合模型参数即可对实验力学性能进行合理的定量估计。
与模拟 DXA 相比，基于 QCT 的 hFE 方法可提供体外椎体强度的定量和显著改善的预测。对于更模拟人体椎体体内情况的加载条件，需要验证这种优越的预测能力。
