Department of Orthopaedics, The Second Affiliated Hospital of Soochow University, Suzhou, China;Department of Orthopaedics, Pudong New Area People's Hospital affiliated to Shanghai University of Medicine - Health Sciences, Shanghai, China.
Department of Surgery, Pudong New Area People's Hospital affiliated to Shanghai University of Medicine - Health Sciences, Shanghai, China.
Acta Orthop Traumatol Turc. 2021 Jan;55(1):9-15. doi: 10.5152/j.aott.2021.20035.
The aim of this study was to evaluate the strength of the locking plate and lag screw construct that is applied in two different working lengths on the simple distal femur fracture model with a finite element analysis (FEA) method.
From the computerized tomography scan data of a 60-year-old healthy male, the AO/OTA 33A1-type fracture model was simulated; the fracture gap was stabilized with the models of locking plate construct with (groups C and D) or without an interfragmentary lag screw (groups A and B). Furthermore, 102-mm plate (groups A and C) and 82-mm plate working lengths (groups B and D) were tested using FEA. Two loading conditions (axial compression and torsion) were applied at the center of the femoral head. Construct stiffness, interfragmentary micromotion, and the peak von Mises stress (VMS) on the plate were assessed.
Group D provided the highest axial stiffness (1347 N/mm), and group A was the weakest (439 N/mm). With the lag screw, shear micromotion remained generally low compared with that without the screw for all axial and torsional load levels and for both plate working lengths, i.e., 0.23 mm with lag screw versus 0.43 mm without lag screw (102 mm working length, 700 N). The percentage decreases of shear micromotion under axial (350/700/1400 N) and torsional loads for the 102-mm working length were >22% and 73%, respectively; while those for the 82-mm working length were >28% and 33%, respectively. The reduction of axial micromotion was observed with the lag screw for all axial load levels as well as for both plate working lengths, i.e., 0.33 mm with lag screw versus 0.87 mm without lag screw (102-mm working length, 700 N). The percentage decreases of axial micromotion under axial loading (350/700/1400 N) for 102 mm and 82 mm working lengths were >42% and 50%, respectively. The peak VMS on the plate stayed generally low with lag screw compared with without lag screw throughout all tested load levels, as well as for both plate working lengths, i.e., 124.26 MPa versus 244.39 MPa (102 mm working length, 700 N). The percentage decreases of the peak VMS under axial (350/700/1400 N) and torsional loads for the 102-mm working length were >40% and 69%, respectively, while those for the 82-mm working length were >47% and 61%, respectively.
The current FEA concludes that in a simple distal femur fracture, adding a lag screw to a locking plate construct provides better torsional stability with a 102-mm plate working length and better axial stability with a 82-mm plate working length. Additionally, the strength of the materials is increased and implant failure can be minimized by using this technique.
本研究旨在通过有限元分析（FEA）方法评估应用于简单股骨远端骨折模型的两种不同工作长度的锁定板和拉力螺钉结构的强度。
从 60 岁健康男性的计算机断层扫描数据中模拟 AO/OTA 33A1 型骨折模型；使用模型锁定板结构（C 组和 D 组）或不使用骨间拉力螺钉（A 组和 B 组）稳定骨折间隙。此外，使用 FEA 测试 102-mm 板（A 组和 C 组）和 82-mm 板工作长度（B 组和 D 组）。在股骨头中心施加两种加载条件（轴向压缩和扭转）。评估结构刚度、骨间微移和板上的峰值 von Mises 应力（VMS）。
D 组提供了最高的轴向刚度（1347 N/mm），A 组最弱（439 N/mm）。对于所有轴向和扭转加载水平以及两种板工作长度，使用拉力螺钉时剪切微动通常比不使用螺钉时低，即有螺钉时为 0.23mm，无螺钉时为 0.43mm（102mm 工作长度，700N）。轴向（350/700/1400N）和扭转加载下 102mm 工作长度的剪切微动百分比降低分别为>22%和 73%；而 82mm 工作长度的分别为>28%和 33%。在所有轴向载荷水平以及两种板工作长度下，使用拉力螺钉均可观察到轴向微动的减少，即有螺钉时为 0.33mm，无螺钉时为 0.87mm（102mm 工作长度，700N）。轴向加载（350/700/1400N）下 102mm 和 82mm 工作长度的轴向微动百分比降低分别为>42%和 50%。在所有测试的载荷水平以及两种板工作长度下，与不使用拉力螺钉相比，板上的峰值 VMS 通常使用拉力螺钉时较低，即 124.26 MPa 对 244.39 MPa（102mm 工作长度，700N）。轴向（350/700/1400N）和扭转载荷下 102mm 工作长度的峰值 VMS 百分比降低分别为>40%和 69%，而 82mm 工作长度的分别为>47%和 61%。
本有限元分析得出结论，在简单的股骨远端骨折中，在锁定板结构中添加拉力螺钉可提供更好的 102mm 板工作长度的扭转稳定性和更好的 82mm 板工作长度的轴向稳定性。此外，通过使用这种技术可以增加材料的强度并最大程度地减少植入物失效的可能性。
