Unit of Biomechanics, Department of Mechanics, School of Applied Mathematical and Physical Sciences, National Technical University of Athens, Zografou Campus, Theocaris Building, 157-73 Attiki, Greece.
Med Eng Phys. 2010 Mar;32(2):145-54. doi: 10.1016/j.medengphy.2009.11.003. Epub 2009 Nov 27.
The present study aims to the design of a finite-element model simulating accurately the pullout behaviour of cylindrical pedicle screws and predicting their pullout force. Three commercial pedicle screws, subjected to pure pullout from synthetic bone, were studied experimentally. The results were used for the design, calibration and validation of a finite-element model. Special attention was paid to the accurate simulation of the failure inside the host material under shear. For this purpose, a bilinear cohesive zone material model was adopted, controlling the mode-II debonding of neighbouring elements in the vicinity of the screw. Comparison between experimental and numerical results proved that the implementation of this approach can significantly enhance the accuracy of the numerical simulation of a screw's mechanical behaviour under pure pullout loads. The numerical model was used for the parametric study of various factors affecting the pullout performance of a cylindrical pedicle screw. It was concluded that the major parameter influencing the pullout force is the outer radius (increasing its value by 36% increases the pullout force by 34%). The influence of the purchase length of the screw is of similar quantitative nature. The respective dependence on the thread inclination, depth and pitch was significantly weaker.
本研究旨在设计一个有限元模型，准确模拟圆柱形椎弓根螺钉的拔出行为，并预测其拔出力。对三种商业椎弓根螺钉进行了纯拔出实验，对合成骨进行了实验研究。实验结果用于有限元模型的设计、校准和验证。特别关注如何准确模拟剪切下宿主材料内部的失效。为此，采用了双线性内聚区材料模型，控制螺钉附近相邻单元的模式 II 脱粘。实验结果与数值结果的比较表明，采用这种方法可以显著提高纯拔出载荷下螺钉力学行为的数值模拟精度。数值模型用于研究各种因素对圆柱形椎弓根螺钉拔出性能的影响。研究结果表明，影响拔出力的主要参数是外半径（增加 36%会使拔出力增加 34%）。螺钉的购买长度的影响具有相似的定量性质。各自对螺纹倾斜度、深度和螺距的依赖性明显较弱。
