Human Performance Laboratory, Faculty of Kinesiology, University of Calgary, 2500 University Dr. NW, Calgary, Alberta T2N 1N4, Canada; McCaig Institute for Bone and Joint Health, University of Calgary, HRIC 3A08, 3280 Hospital Drive NW, Calgary, Alberta T2N 4Z6, Canada.
McCaig Institute for Bone and Joint Health, University of Calgary, HRIC 3A08, 3280 Hospital Drive NW, Calgary, Alberta T2N 4Z6, Canada; Department of Surgery, Department of Community Health Sciences, Cumming School of Medicine, Foothills Campus, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta T2N 4N1, Canada.
Bone. 2018 May;110:295-303. doi: 10.1016/j.bone.2018.02.015. Epub 2018 Feb 23.
Atypical femoral fractures (AFF) are characterized as low-energy fractures of the femoral shaft or subtrochanteric region. Femoral geometry is known to play a role in AFF risk; it is hypothesized that high-risk geometries are associated with elevated femoral shaft strain. However, it is not well known which geometric parameters have the greatest effect on strain, or whether interaction between parameters is significant. The purpose of this study was to thoroughly quantify the relationship between femoral geometry and diaphyseal strain, using patient specific finite element (FE) modelling in concert with parametric mesh morphing.
Ten FE models were generated from computed tomography (CT) images of cadaveric femora. Heterogeneous material properties were assigned based on average CT intensities at element locations and models were subject to loads and boundary conditions representing the stance phase of gait. Mesh morphing was used to manipulate 8 geometric parameters: neck shaft angle (NSA), neck version angle (NV), neck length (NL), femoral length (FL), lateral bowing angle (L.Bow), anterior bowing angle (A.Bow), shaft diameter (S.Dia), and cortical bone thickness (C·Th). A 2-Level full factorial analysis was used to explore the effect of different combinations of physiologically realistic minimum and maximum values for each parameter. Statistical analysis (Generalized Estimating Equations) was used to assess main effects and first order interactions of each parameter.
Six independent parameters and seven interaction terms had statistically significant (p<0.05) effects on peak strain and strained volume. For both measures, the greatest changes were caused by S.Dia, L.Bow, and A.Bow, and/or first order interactions involving two of these variables.
As hypothesized, a large number of geometric measures (six) and first order interactions (seven) are associated with changes in femoral shaft strain. These measures can be evaluated radiographically, which may have important implications for future studies investigating AFF risk in clinical populations.
非典型股骨骨折（AFF）的特征是股骨骨干或转子下区域的低能量骨折。已知股骨几何形状在 AFF 风险中起作用；据推测，高风险几何形状与股骨骨干应变升高有关。然而，目前尚不清楚哪些几何参数对应变的影响最大，或者参数之间的相互作用是否显著。本研究的目的是使用特定于患者的有限元（FE）建模与参数化网格变形相结合，彻底量化股骨几何形状与骨干应变之间的关系。
从尸体股骨的计算机断层扫描（CT）图像中生成了 10 个 FE 模型。根据元素位置的平均 CT 强度分配了不均匀的材料特性，并且模型受到了代表步态站立阶段的载荷和边界条件的作用。使用网格变形来操纵 8 个几何参数：颈干角（NSA）、颈倾斜角（NV）、颈长度（NL）、股骨长度（FL）、外侧弯曲角（L.Bow）、前弯曲角（A.Bow）、骨干直径（S.Dia）和皮质骨厚度（C·Th）。使用 2 级完全因子分析来探索每个参数的生理现实最小值和最大值的不同组合的效果。使用广义估计方程进行统计分析（Generalized Estimating Equations），以评估每个参数的主要影响和一阶交互作用。
六个独立参数和七个一阶交互项对峰值应变和应变体积有统计学意义（p<0.05）。对于这两个指标，S.Dia、L.Bow 和 A.Bow 的变化最大，或者涉及其中两个变量的一阶交互作用。
正如假设的那样，大量的几何测量值（六个）和一阶交互项（七个）与股骨骨干应变的变化有关。这些测量值可以通过影像学评估，这可能对未来研究临床人群中的 AFF 风险具有重要意义。
