不同螺纹C2椎弓根拉力螺钉系统固定治疗枢椎环骨折的有限元分析

C2 pedicle lag screws with different thread designs for the fixation of axis ring fractures: a finite-element analysis

中文关键词:  枢椎环骨折  C2椎弓根拉力螺钉  有限元  双螺纹  半螺纹

英文关键词:Axis ring fracture  C2 pedicle lag screw  Finite element  Double thread  Single thread

中文摘要:

  【摘要】 目的：比较半螺纹、双螺纹、全螺纹C2椎弓根拉力螺钉系统固定治疗枢椎环骨折的生物力学特性，为临床选择椎弓根螺钉提供参考。方法：获取1名28岁健康成年男性志愿者的C0～C3节段薄层CT扫描数据，建立正常颈椎C0～C3节段三维六面体网格有限元原始模型。参照既往枢椎环骨折C2椎弓根骨折分型，通过弱化网格单元强度的方法在原始模型上建立A、B、C三种枢椎环骨折模型：A型骨折模型，双侧椎弓根对称性骨折；B型骨折模型，单侧上关节突及椎体后壁骨折，伴对侧椎弓根骨折；C型骨折模型，双侧上关节突骨折，伴椎体后壁骨折。分别用单螺纹、双螺纹及全螺纹椎弓根拉力螺钉系统模拟固定C2-3节段，在模型枕骨髁部施加50N垂直向下压力模拟头颅重力，同时施加1.5N·m力矩使模型加载前屈、后伸、侧屈及旋转四种生理载荷，比较各固定模型在各工况下节点路径上的位移及应力分布情况。结果：固定A型骨折模型后，单螺纹螺钉在各工况下节点路径上的最大位移均小于双螺纹螺钉和全螺纹螺钉；固定B型骨折模型后，单螺纹及双螺纹螺钉各工况下节点路径上的最大位移小于全螺纹螺钉，单螺纹螺钉在前屈、后伸工况下节点路径上的最大位移小于双螺纹螺钉，在侧屈及旋转工况下节点路径上的最大位移大于双螺纹螺钉；固定C型骨折模型后，单螺纹螺钉各工况下节点路径各方向上的最大位移均大于双螺纹螺钉和全螺纹螺钉。固定不同类型骨折的应力极值，A型骨折模型，单螺纹螺钉的应力极值最小，全螺纹螺钉在前屈及后伸工况下应力极值大于双螺纹螺钉，侧曲与旋转小于双螺纹螺钉；B型骨折模型，除旋转工况外，单螺纹螺钉的应力极值均最小；C型骨折模型，单螺纹螺钉的应力极值最小，全螺纹螺钉的应力极值最大。单螺纹螺钉应力主要集中在骨折断端附近及尾端钉帽与椎体表面接触区域，应力极值在骨折断端螺杆处；双螺纹螺钉和全螺纹螺钉应力主要集中在头端螺纹与尾端螺纹，钉帽与椎体后表面接触部位应力较小，应力极值在尾端螺纹与骨皮质交接处。结论：单螺纹螺钉固定B型骨折椎体后壁及上关节突一侧及C型骨折的生物力学效果更佳；双螺纹螺钉固定A型骨折及B型骨折椎弓根骨折一侧生物力学效果更好；全螺纹螺钉在固定所有骨折类型的生物力学性能均不及单螺纹和双螺纹螺钉。

英文摘要:

  【Abstract】 Objectives: To compare the biomechanical characteristics of C2 pedicle lag screws of single-thread, double-thread, and full-thread in the fixation of axis ring fractures, and to provide reference for clinical selection of different types of pedicle lag screws. Methods: The thin-section CT scan data of the C0-C3 segments of a healthy 28-year-old male adult volunteer were obtained to establish the original model of 3D hexahedral mesh finite element of normal C0-C3 segment. According to the previous classification of C2 pedicle fracture of axis ring fracture, three C2 pedicle fracture models of A, B and C were established on the original model by weakening the strength of mesh unit. The C2-3 segment was simulatedly fixed with single-threaded, double-threaded and full-threaded screw models, respectively. A 50N vertically downward pressure was applied to the occipital condyle of the model to simulate the head gravity, and a 1.5N·m torque was applied to the model to load the four physiological loads of flexion, extension, lateral flexion and rotation. The displacement and stress distribution of the fracture end nodes of each fixed model under different working conditions were compared. Results: In fracture model A under all motion conditions, the maximum displacement of the node path of single-threaded screw was smaller than that of the double-threaded screw and full-threaded screw; In model B, single-threaded screw and double-threaded screw were smaller than full-threaded screw in the maximum displacement of node path under all motion conditions, while single-threaded screw was smaller than double-threaded screw in the maximum displacement of node path under flexion and extion, and greater than double-threaded screw under lateral bending and rotation conditions; In model C, the maximum displacement of the single-threaded screw in each direction of the node path was all greater than that of the double-threaded screw and the full-threaded screw. In terms of extreme stress value, in fracture model A, single-threaded screw was the smallest, full-threaded screw was greater under flexion and extension conditions and smaller under lateral bending and rotation conditions than double-threaded screw; in model B, single-threaded screw was the smallest except the rotation condition; in model C, single-threaded screw was the smallest and full-threaded screw was the largest. The stress of the single-threaded screw was mainly concentrated near the fracture end and the contact area between the nail cap and the surface of vertebral body, and the extreme stress was at the screw end of the fracture end; The stress of double-threaded screw and full-threaded screw was mainly concentrated in the head end thread and tail end thread, the stress of the contact area between the nail cap and the posterior surface of vertebral body was small, and the extreme stress value was at the junction of the tail end thread and the cortical bone. Conclusions: The biomechanical effect of single-threaded screw fixation of the posterior wall of vertebral body and the side of superior articular process of type B fracture and type C fracture is better. Double-threaded screw fixation of type A fracture and the pedicle fracture side of type B fracture is better in biomechanical effect; The biomechanical properties of full-threaded screw are not as good as single-threaded and double-threaded screws in fixing all fracture types.