新型钉尾横连在后路寰枢椎内固定中的三维有限元分析

Three-dimensional finite element analysis of a new horizontal screw-screw crosslink in posterior atlantoaxial internal fixation

背景:在寰枢关节疾病采用后路寰枢椎椎弓根螺钉内固定术(C_(1)-C_(2)pedicle screw-rod fixation,C_(1)-C_(2)PSR)中加用传统的棒-棒横连可以为螺钉/棒结构提供更坚固抗旋转稳定性,但有安装困难、影响植骨床和脊髓损伤的风险。作者设计的新型寰椎钉尾横连(horizontal screw-screw crosslink,hS-S CL)可以有效克服上述缺点,但其生物力学性能尚不清楚。目的:利用三维有限元分析新型寰椎钉尾横连在C_(1)-C_(2)PSR中的生物力学特性。方法:采集1名成人健康男性志愿者枕骨底到枢椎(C0-2)的CT薄层扫描数据,分别建立寰枢椎有限元模型:正常组、失稳组、失稳+C_(1)-C_(2)PSR(无横连组)、C_(1)-C_(2)PSR+hS-S CL(钉尾横连组)。对各个有限元模型加载1.5 Nm的扭矩,计算出4组模型在屈伸、左右侧屈、左右旋转工况下的活动度及横连应力峰值,并提取内固定应力云图。结果与结论:①失稳组较正常组的运动范围明显增大43.8%-78.7%;2种内固定组在6种工况下的运动范围较失稳组减少90.2%-98.7%,在屈伸状态下的运动范围基本一致,但在侧屈及旋转状态下,钉尾横连组较无横连组运动范围分别减少34.3%-43.8%和78.6%-79.1%,其中在旋转状态运动范围减少最为明显;②2种内固定内植物模型应力峰值:钉尾横连组最大应力总体上小于无横连组,内固定组在后伸时应力峰值最小;③内植物的应力云图:显示内固定未出现明显的应力集中现象,且主要的应力分布区域为螺钉根部与骨质结合部,横连两端与螺钉尾槽或连接棒结合部;④新型钉尾横连能明显提高内固定的抗旋转稳定性,在三维运动上承担部分应力,降低内植物的最大应力;钉尾横连两端的应力分布明显,该部位可能出现横连的断裂。

BACKGROUND:The addition of traditional rod-rod fixation for atlantoaxial joint disease to C_(1)-C_(2)pedicle screw-rod fixation(C_(1)-C_(2)PSR)can provide stronger anti-rotation stability for screw/rod fixation,but there is a risk of installation difficulties,impact on bone graft bed,and spinal cord injury.The new horizontal screw-screw crosslink(hS-S CL)designed by the authors can effectively overcome the above shortcomings,but its biomechanical properties are unclear.OBJECTIVE:To analyze biomechanical properties of new horizontal screw-screw crosslink in C_(1)-C_(2)PSR by three-dimensional finite element analysis.METHODS:CT thin layer scanning data were collected from the occipital base to the axis(C0-2)of one adult healthy male volunteer.The atlantoaxial finite element models were established respectively:the normal group,the unstable group,the non-crosslink group(unstable+C_(1)-C_(2)PSR),and the crosslink group(C_(1)-C_(2)PSR+hS-S CL).Range of motion and Von Miss Stresses in flexion and extension,lateral flexion and rotation of the four groups were calculated by applying 1.5 Nm torque to each finite element model,and the stress cloud was extracted.RESULTS AND CONCLUSION:(1)Range of motion of the unstable group was increased by 43.8%-78.7%compared with the normal group,and the range of motion of the internal fixation groups was 90.2%-98.7%lower than that of the unstable group under six conditions.The range of motion of the crosslink group and the non-crosslink group was basically the same in flexion and extension states,but in lateral flexion and rotation states,the range of motion of the crosslink group decreased 34.3%-43.8%and 78.6%-79.1%,respectively,compared with the non-crosslink group,and range of motion decreased most obviously in rotation state.(2)The stress peak of the internal plant model:The maximum stress of the crosslink group was generally smaller than that of the non-crosslink group,and the stress peak value of all the internal fixation groups was the lowest when the extension was carried out.(3)The stress cloud of internal plants showed that there was no obvious stress concentration phenomenon in the internal fixation,and the main stress distribution areas were the screw root and bone joint,and the crosslink ends were the screw tail groove or the joint rod joint.(4)The new horizontal screw-screw crosslink can obviously improve the antirotation stability of internal fixation and it can share part of the pressure in the three-dimensional motion direction of the internal fixation system and reduce the maximum stress of the internal plants.However,the stress distribution is obvious at both ends of the crosslink,and this part may be prone to fracture of the crosslink.