Department of Physics and Mathematics, University of Eastern Finland, Kuopio, Finland.
Biomech Model Mechanobiol. 2011 Jul;10(4):529-38. doi: 10.1007/s10237-010-0253-3. Epub 2010 Sep 1.
Measurement of bone mineral density (BMD) by DXA (dual-energy X-ray absorptiometry) is generally considered to be the clinical golden standard technique to diagnose osteoporosis. However, BMD alone is only a moderate predictor of fracture risk. Finite element analyses of bone mechanics can contribute to a more accurate prediction of fracture risk. In this study, we applied a method to estimate the 3D geometrical shape of bone based on a 2D BMD image and a femur shape template. Proximal femurs of eighteen human cadavers were imaged with computed tomography (CT) and divided into two groups. Image data from the first group (N = 9) were applied to create a shape template by using the general Procrustes analysis and thin plate splines. This template was then applied to estimate the shape of the femurs in the second group (N = 9), using the 2D BMD image projected from the CT image, and the geometrical errors of the shape estimation method were evaluated. Finally, finite element analysis with stance loading condition was conducted based on the original CT and the estimated geometrical shape to evaluate the effect of the geometrical errors on the outcome of the simulations. The volumetric errors induced by the shape estimation method itself were low (<0.6%). Increasing the number of bone specimens used for the template decreased the geometrical errors. When nine bones were used for the template, the mean distance difference (±SD) between the estimated and the CT shape surfaces was 1.2 ± 0.3 mm, indicating that the method was feasible for estimating the shape of the proximal femur. Small errors in geometry led systematically to larger errors in the mechanical simulations. The method could provide more information of the mechanical characteristics of bone based on 2D BMD radiography and could ultimately lead to more sensitive diagnosis of osteoporosis.
双能 X 射线吸收法（DXA）测量骨密度（BMD）通常被认为是诊断骨质疏松症的临床金标准技术。然而，BMD 本身只是骨折风险的中度预测指标。骨骼力学的有限元分析可以帮助更准确地预测骨折风险。在这项研究中，我们应用了一种方法，根据二维 BMD 图像和股骨形状模板来估计骨骼的三维几何形状。对 18 具人体尸体的股骨进行了计算机断层扫描（CT）成像，并将其分为两组。第一组（N=9）的图像数据用于通过总体 Procrustes 分析和薄板样条创建形状模板。然后，使用从 CT 图像投影的二维 BMD 图像，将该模板应用于第二组（N=9）的股骨形状估计，评估形状估计方法的几何误差。最后，根据原始 CT 和估计的几何形状进行站立加载条件下的有限元分析，以评估几何误差对模拟结果的影响。形状估计方法本身引起的体积误差较低（<0.6%）。增加用于模板的骨骼标本数量可以减少几何误差。当使用 9 块骨头作为模板时，估计形状和 CT 形状表面之间的平均距离差（±SD）为 1.2±0.3mm，表明该方法可用于估计股骨近端的形状。较小的几何误差会导致机械模拟中的误差系统地增大。该方法可以基于二维 BMD 射线照相提供更多关于骨骼机械特性的信息，并最终导致骨质疏松症的更敏感诊断。
