Abstract：
Atypical femoral fractures (AFFs) are categorized as low-energy fractures of the femoral shaft or subtrochanteric region. The use of computed tomography-based finite element analysis demonstrated that the femoral weakest point against tensile stress coincided with AFF location, which was determined by the lower limb axis and femoral bowing.
BACKGROUND: This study aimed to assess the relationship between the femoral weakest point against tensile stress and the lower limb axis and geometry, including femoral bowing, using a computed tomography (CT)-based finite element analysis (FEA) model.
METHODS: We retrospectively reviewed 19 patients with AFFs and analyzed their CT images of the contralateral intact femur. We performed FEA to find the maximum principal stress (MPS) and maximal tensile stress loading area (femoral weakest point, FWP) of each patient and matched the FWP with the real location of AFF. We applied mechanical axes differently, as neutral, varus, and valgus, in the FEA model, when we analyzed the change in MPS and FWP based on lower limb alignment. We compared the degree of agreement between the real fracture location and FWP before and after knee mechanical axis adjustment.
RESULTS: The average participant age was 75.9 (range, 61-87) years, and all participants were women. In the 19 patients included, we observed 20 and 7 shaft and subtrochanteric AFFs, respectively. The average mechanical axis at the knee joint level was 22.6 mm (range, 0-70 mm) of the varus. All the patients showed an increasing trend of MPS and a distal movement of FWP when the mechanical axis of the knee was applied from the valgus to varus alignment. The root mean square errors between the FWP and real fracture location were 14.58% and 10.87% before and after adjustment, respectively, implying that the degree of agreement was better in patients who underwent mechanical adjustment.
CONCLUSIONS: The use of CT/FEA demonstrated that the FWP against tensile stress coincided with AFF location, which was determined by the lower limb axis and femoral bowing.
BACKGROUND: This study aimed to assess the relationship between the femoral weakest point against tensile stress and the lower limb axis and geometry, including femoral bowing, using a computed tomography (CT)-based finite element analysis (FEA) model.
METHODS: We retrospectively reviewed 19 patients with AFFs and analyzed their CT images of the contralateral intact femur. We performed FEA to find the maximum principal stress (MPS) and maximal tensile stress loading area (femoral weakest point, FWP) of each patient and matched the FWP with the real location of AFF. We applied mechanical axes differently, as neutral, varus, and valgus, in the FEA model, when we analyzed the change in MPS and FWP based on lower limb alignment. We compared the degree of agreement between the real fracture location and FWP before and after knee mechanical axis adjustment.
RESULTS: The average participant age was 75.9 (range, 61-87) years, and all participants were women. In the 19 patients included, we observed 20 and 7 shaft and subtrochanteric AFFs, respectively. The average mechanical axis at the knee joint level was 22.6 mm (range, 0-70 mm) of the varus. All the patients showed an increasing trend of MPS and a distal movement of FWP when the mechanical axis of the knee was applied from the valgus to varus alignment. The root mean square errors between the FWP and real fracture location were 14.58% and 10.87% before and after adjustment, respectively, implying that the degree of agreement was better in patients who underwent mechanical adjustment.
CONCLUSIONS: The use of CT/FEA demonstrated that the FWP against tensile stress coincided with AFF location, which was determined by the lower limb axis and femoral bowing.
摘要：
非典型股骨骨折（AFF）被归类为股骨干或转子下区域的低能量骨折。使用基于计算机断层扫描的有限元分析表明，抗拉应力的股骨最弱点与AFF位置一致，由下肢轴和股骨弯曲决定。
背景：这项研究旨在评估抗拉应力的股骨最弱点与下肢轴和几何形状之间的关系，包括股骨弯曲，使用基于计算机断层扫描(CT)的有限元分析(FEA)模型。
方法：我们回顾性分析了19例AFFs患者的对侧完整股骨的CT图像。我们进行了有限元分析，以找到最大主应力（MPS）和最大拉伸应力加载区域（股骨最弱点，每位患者的FWP），并将FWP与AFF的真实位置进行匹配。我们以不同的方式应用机械轴，作为中立,varus,和外翻，在FEA模型中，当我们根据下肢排列分析MPS和FWP的变化时。我们比较了膝关节机械轴调整前后真实骨折位置与FWP的吻合程度。
结果：参与者平均年龄为75.9岁（范围，61-87）年，所有参与者都是女性。在包括的19名患者中，我们观察了20和7个轴和转子下AFF，分别。膝关节水平的平均机械轴为22.6mm（范围，0-70毫米）的内翻。当膝关节的机械轴从外翻到内翻对准时，所有患者均显示出MPS增加的趋势和FWP的远端运动。调整前后FWP与真实裂缝位置的均方根误差分别为14.58%和10.87%,分别,这意味着接受机械调整的患者的一致性程度更好。
结论：CT/FEA的使用表明，抗拉应力的FWP与AFF位置一致，由下肢轴和股骨弯曲决定。
背景：这项研究旨在评估抗拉应力的股骨最弱点与下肢轴和几何形状之间的关系，包括股骨弯曲，使用基于计算机断层扫描(CT)的有限元分析(FEA)模型。
方法：我们回顾性分析了19例AFFs患者的对侧完整股骨的CT图像。我们进行了有限元分析，以找到最大主应力（MPS）和最大拉伸应力加载区域（股骨最弱点，每位患者的FWP），并将FWP与AFF的真实位置进行匹配。我们以不同的方式应用机械轴，作为中立,varus,和外翻，在FEA模型中，当我们根据下肢排列分析MPS和FWP的变化时。我们比较了膝关节机械轴调整前后真实骨折位置与FWP的吻合程度。
结果：参与者平均年龄为75.9岁（范围，61-87）年，所有参与者都是女性。在包括的19名患者中，我们观察了20和7个轴和转子下AFF，分别。膝关节水平的平均机械轴为22.6mm（范围，0-70毫米）的内翻。当膝关节的机械轴从外翻到内翻对准时，所有患者均显示出MPS增加的趋势和FWP的远端运动。调整前后FWP与真实裂缝位置的均方根误差分别为14.58%和10.87%,分别,这意味着接受机械调整的患者的一致性程度更好。
结论：CT/FEA的使用表明，抗拉应力的FWP与AFF位置一致，由下肢轴和股骨弯曲决定。
