Bianco Rohan-Jean, Arnoux Pierre-Jean, Wagnac Eric, Mac-Thiong Jean-Marc, Aubin Carl-Éric
*Department of Mechanical Engineering, Polytechnique Montréal †Sainte-Justine University Hospital Center, Montreal, QC, Canada ‡Laboratoire de Biomécanique Appliquée, UMRT24 IFSTTAR/Aix-Marseille Université, Marseille, France §Department of Surgery, Université de Montréal ∥Department of Surgery, Hôpital du Sacré-Cœur de Montréal, Montréal, QC, Canada.
Clin Spine Surg. 2017 Apr;30(3):E226-E232. doi: 10.1097/BSD.0000000000000151.
Detailed biomechanical analysis of the anchorage performance provided by different pedicle screw designs and placement strategies under pullout loading.
To biomechanically characterize the specific effects of surgeon-specific pedicle screw design parameters on anchorage performance using a finite element model.
Pedicle screw fixation is commonly used in the treatment of spinal pathologies. However, there is little consensus on the selection of an optimal screw type, size, and insertion trajectory depending on vertebra dimension and shape.
Different screw diameters and lengths, threads, and insertion trajectories were computationally tested using a design of experiment approach. A detailed finite element model of an L3 vertebra was created including elastoplastic bone properties and contact interactions with the screws. Loads and boundary conditions were applied to the screws to simulate axial pullout tests. Force-displacement responses and internal stresses were analyzed to determine the specific effects of each parameter.
The design of experiment analysis revealed significant effects (P<0.01) for all tested principal parameters along with the interactions between diameter and trajectory. Screw diameter had the greatest impact on anchorage performance. The best insertion trajectory to resist pullout involved placing the screw threads closer to the pedicle walls using the straightforward insertion technique, which showed the importance of the cortical layer grip. The simulated cylindrical single-lead thread screws presented better biomechanical anchorage than the conical dual-lead thread screws in axial loading conditions.
The model made it possible to quantitatively measure the effects of both screw design characteristics and surgical choices, enabling to recommend strategies to improve single pedicle screw performance under axial loading.
对不同椎弓根螺钉设计及置入策略在拔出载荷下提供的锚固性能进行详细的生物力学分析。
使用有限元模型从生物力学角度表征外科医生特定的椎弓根螺钉设计参数对锚固性能的具体影响。
椎弓根螺钉固定常用于治疗脊柱疾病。然而，对于根据椎体尺寸和形状选择最佳螺钉类型、尺寸及置入轨迹，目前几乎没有共识。
采用实验设计方法对不同的螺钉直径、长度、螺纹及置入轨迹进行计算机测试。创建了一个详细的L3椎体有限元模型，包括弹塑性骨特性以及与螺钉的接触相互作用。对螺钉施加载荷和边界条件以模拟轴向拔出试验。分析力-位移响应和内部应力以确定每个参数的具体影响。
实验设计分析显示，所有测试的主要参数以及直径与轨迹之间的相互作用均具有显著影响（P<0.01）。螺钉直径对锚固性能影响最大。抵抗拔出的最佳置入轨迹是使用直接置入技术将螺纹靠近椎弓根壁放置，这表明了皮质层握持的重要性。在轴向加载条件下，模拟的圆柱形单导程螺纹螺钉比圆锥形双导程螺纹螺钉具有更好的生物力学锚固性能。
该模型能够定量测量螺钉设计特征和手术选择的影响，从而能够推荐在轴向加载下改善单个椎弓根螺钉性能的策略。
