不同置钉角度下腰骶椎椎弓根螺钉固定加椎间融合的有限元生物力学比较研究

Biomechanical comparison of different nailing angles in pedicle screw fixation plus intervertebral fusionin lumbosacral finite element models

目的比较不同置钉角度下腰骶椎椎弓根螺钉同定加椎间融合的有限兀生物力学性能，以确定最佳的椎弓根螺钉固定角度。方法通过CT扫描、Mimicsl3．0软件i维重建、Freeform6．0表面处理和Ansys10，0软件前处理等方法建立正常L4～S1，节段有限元模犁，并据此建立去除L5～S。椎间盘后椎弓根螺钉后路固定加椎间融合模型。根据不同置钉角度分为3纰：模型1组：上、下位螺钉水平位内置0。，矢状位与终板平行；模型2组：上、下位螺钉水平位内置15°，矢状位与终板平行；模型3组：上位螺钉水平位内置0°、矢状位上翘15°，下位螺钉水平位内置0°、矢状化位与板平行。在这3组模型上分别加载5N·m的前屈、后仲、左侧弯和左旋转扭矩载荷，计算各组钉棒结构、椎间融合器及L4～S1，的应力分布值。结果在前屈、后伸、左侧弯和左旋转4种状态下，模型2组的钉棒结构、椎问融合器、L4、L5和S1的最大应力值均处于最低水平，前屈时分别为2．96×10^7、5．65×10^5．76×10^6、8．06×10^6、8．51×10^6N／m2，后伸时分别为2．98×10^6、6．08×10^6、6．49×10^6、8．63×10^6、9．17×10^6 N／in：，侧弯时分别为3．06×10^7、9．71×10^6、2．39×10^6、1．14×10^6、8．6l×10^6N／mL，左旋转时分别为2．96×10^7、1．00×10^6、5．76x10^6、8．06×10^6、8．51×10^6N／m2。除左旋转以外，其他3种静载状态下模型l组的钉棒结构和椎问融合器最大应力值均低于模型3组。结论腰骶椎后路椎弓根螺钉闻定加椎问融合时，矢状位与终板平行、水平位内倾一定角度有助于改善整体结构的应力水平，缓解螺钉和椎体结构的应力集中，从而避免断钉、断棒及螺钉松动的发生。

Objective To determine the optimal nailing angle by comparing the biomechanical properties of different nailing angles in pedicle screw fixation plus intervertebral fusion in lumbosacral finite element models. Methods We established the finite element models of normal lumbosacral vertebral IA-SI segments whose intervertebral disc of L5-SI was removed using CT scan, three-dimensional recon- struction by software Mimicsl3.0, surface treatment by software Freeform6.0 and preprocessing by software Ansysl0. O, respectively. Fixation with posterior pedicle screws and intervertebral fusion was simulated in the finite element models. The models were divided into 3 groups according to the different nailing angles. Model 1： the screws above and below were inserted by angle of 0~ transversely with the sagittal view parallel to the end plate. Model 2： the screws above and below were inserted by an angle of 15° transversely with the sagittal view parallel to the end plate. Model 3： the screw above was inserted by an angle of 0° transversely with the sagittal view uplifted by an angle of 15° while the screw below was inserted by an angle of 0° transversely with the sagittal view parallel to the end plate. Then all the models were subjected to torque loads of 5 N · m at anteflexion, posterior extension, left bending and left rotation respectively. The stress distributions ofscrew-rod system, cage, L4. i,5 and S1 were analyzed and compared between the 3 groups. Results The stress distributions of screw-rod system, cage, L4, L5 and SI at anteflexion, posterior extension, left bending and left rotation were the lowest in Model 2. The stress distributions of screw-rod system, cage, 1,4, L5 and SI were respectively 2.96 x 107, 5.65 x l06, 5.76 x 106, 8.06 10 aod 8.51 x 106 N/m2 at anteflexion, re- spectively 2. 98x107, 6. 08x106, 6.49x106, 8.63x106 and 9. 17x106 N/m2 at posterinr extension, respectively 3.06 x 107. 9.71 x 106, 2.39 x 106, 1. 14 x 106 and 8.61 x 106 N/m-＇ at left bending, and re- spectively 2. 96 x 107, 1.00 x 106, 5.76 x 106, 8.06 x 106 and 8.51 x 106 N/m2 at left rotation. The max- imum stresses of screw-rod system and cage in Model l were lower than in Model 3 at anteflexion, posterior extension and left bending. Conclusion In fixation of lumbosacral posterior pedicle screw and interver- tebral fusion, screws parallel to the end plate in the sagittal view and inserted by an inclined inward angle in the transverse position can improve the stress of the whole structure and ease the concentrated stress on screws and vertebral body, preventing breaking and loosening of screw-rod system.