基于有限元的椎弓根螺钉结合两种材质椎间融合器治疗腰椎滑脱症的生物力学特性研究

Biomechanical evaluation of pedicle screw fixation combined with cages of different materials in treatment of lumbar spondylolisthesis by finite element analysis

摘要:

目的 通过有限元分析方法评估椎弓根螺钉结合两种材质椎间融合器在治疗腰椎滑脱症中的生物力学性能。方法 选取健康男性志愿者1名,使用螺旋CT扫描脊柱L4～L5节段，采用Mimics和Geomagic软件对CT图像进行三维模型重构并导入有限元分析软件ANSYS 12.0建立正常L4～L5节段三维有限元模型（INT）。在此基础上，模拟两种材质融合器结合椎弓根钉固定的模型，双侧椎弓根螺钉+Ti(钛)椎间融合器（M1），双侧椎弓根螺钉+ PEEK(聚醚醚酮)椎间融合器（M2）。对模型施加400N预载荷，运动附加力为6 N·m，定义模型约束和载荷条件后，在腰椎前屈、后伸、左右侧屈及左右旋转六种工况下计算L4～L5节段角位移及椎弓根螺钉和融合器所受应力。结果 M1，M2在各种工况的角位移均小于INT。应力实验中，M1融合器应力峰值在各种工况下均高于M2。后伸位时，M1与M2的螺钉及椎间融合器的应力峰值较其他工况小。结论 椎弓根内固定可以提供融合节段足够的稳定性。对于融合节段在椎弓根钉提供相同稳定性的条件下，PEEK材质融合器应力峰值均较Ti材质融合器小，PEEK材质融合器发生沉降及移位的可能性低于Ti材质融合器，所以其融合率相对较高。后伸位时所受应力较小，由此推测后伸位为较稳定的位置。

Abstract:

【Objective】 To evaluate the biomechanical characteristics of pedicle screw fixation combined with cages of different materials in the treatment of lumbar spondylolisthesis. 【Methods】 A three-dimensional finite element model of intact L4~L5 segments was constructed by using CT scans of a healthy male. Materia-lise's interactive medical image control system 10.01(Mimics 10.01), Geomagic 10.0 and the finite element program ANSYS 12.0 were applied to the model． Based on the intact L4～L5 model (INT) , the simulations of the cages of different materials were established with bilateral pedicle screws combined titanium material cages (M1 model) and bilateral pedicle screws combined PEEK material cages (M2 model ). Then 6 N·m moments with 400 N preload were applied to L3 vertebral body under the loading conditions of extension, flexion, lateral bending and torsion, respectively. The L4~L5 angular variation and stress distribution in pedicle screw and cage under different load were documented. 【Results】 The angular variations of fusion models (M1 and M2) were less than that of the normal lumbar spine model (INT). During the stress experiments, the peak stress of M1 under various conditions was higher than that of M2. Under the extension condition, the peak stress of screws and cages was lower than that under other working conditions. 【Conclusions】 Pedicle screw fixation can provide sufficient stability in fusion segment. For the same stability condition of pedicle fixations, PEEK material cages have smaller peak stress and less possibility of cages collapse and displacement than titanium material cages, so they have a relatively higher fusion rate. Under the extension condition both cages and screws have less stress. Therefore, we infer extension position is a stable position.