腰椎间融合后路非对称与对称固定螺钉应力的有限元比较

背景：经椎间孔腰椎间融合非对称固定的生物力学稳定性研究，发现固定效果与双侧椎弓根螺钉接近，可满足临床应用所需生物力学要求。经关节突椎弓根螺钉参与经椎间孔腰椎间融合非对称固定的螺钉力学安全性又会怎样呢？目的：建立L4＋s功能节段左侧经椎间孔腰椎间融合后，分别予以同侧椎弓根螺钉＋对侧经关节突椎弓根螺钉、同侧椎弓根螺钉＋对侧经椎板关节突螺钉及双侧椎弓根螺钉固定的三维有限元模型，施加相同的载荷，分析不同运动状态下螺钉应力分布特点，比较3种螺钉应力状况。方法：对一成人正常L4—5椎节段标本、椎间融合器、椎弓根螺钉和皮质骨螺钉进行64排螺旋CT扫描，通过Mimicsll．1建立左侧经椎间孔腰椎间融合后3种内固定组合（同侧椎弓根螺钉＋对侧经椎板关节突螺钉、同侧椎弓根螺钉＋对侧经关节突椎弓根螺钉及双侧椎弓根螺钉固定）的几何模型，利用Simpleware3．1软件分别建立三维有限元模型，模拟500N惦Nm载荷下前屈、后伸、左＼右侧弯、左＼右侧旋等6种运动状态，用Abaqus6．8软件进行螺钉应力变化和分布特点分析。结果与结论：由于经椎间孔腰椎间融合入路切除了左侧关节突，造成内植物应力分布不对称，对弹性模量大的内固定器械一椎弓根螺钉应力影响最大，尤其是在左旋运动时。在不对称组合内固定中，由于关节突关节螺钉的使用，使对侧椎弓根螺钉应力相应增加，以左旋运动时尤为明显，但关节突关节螺钉断裂的危险性增高不明显。提示为降低螺钉断裂的风险，经椎间孔腰椎间融合后路3种组合内固定均应严格限制旋转运动，尤其是关节突切除侧的旋转运动。

Screw stress features of the posterior asymmetric or symmetric fixation of transforaminal lumbar fusion based on a three-dimensional finite element method

BACKGROUND： Biomechanical investigation had discovered that effectiveness of the posterior asymmetric fixation based on transforaminal lumbar fusion is similar to double side pedicle screws fixation, which can meet the clinical biomechanical requirement. How is the transfacetopedicular screw security in posterior asymmetric fixation after transforaminal lumbar fusion？ OBJECTIVE： To develop three-dimensional finite element model of L4-s segment treated with posterior ipsilatera pedicle screws supplemented with contralateral transfacetopedicular screw fixation, posterior ipsilateral pedicle screws supplemented with contralateral translaminarfacet screw fixation and posterior bilateral pedicle screws fixation after transforamina! lumbar fusion respectively and treated with the same load, in order to evaluate the stress of the screws under different kinestates and the stress of three kinds of screws combined fixation in transforaminal lumbar fusion. METHODS： The geometrical model was created by Mimics 11.1 based on CT data of L4/5 motion segment, fusion cage, pedicle screws and os integumentale screw from an adult man. Different fixation models after left transforaminal lumbar fusion including the following sequentially test configurations： ipsilateral pedicle translaminarfacet screw; ipsilateral pedicle screws＋contralateral transfacetopedicular screw; bilateral pedicle screws. Subsequently, the above models were imported into the Simpleware 3.1 in order to establish the three-dimensional finite element models. 500 N／6 Nm loading was loaded on the upper surface of L of trensforaminal lumbar fusion supplement with three types of fixations to simulate lumbar flexion, extension, lateral bending and axial rotation. The three-dimensional finite element models were imported into Abaqus 6.8 to analyze the stress changes and stress distribution of screws. RESULTS AND CONCLUSION： Left facet joint was removed in transforaminal lumbar fusion procedure, leading to asymmetry stress attribution of internal implants. For rigid pedicle screws fixation, they were more influenced by asymmetry stress attribution, especially under left axial rotation. In asymmetry fixation, the stress of ipsilateral pedicle screws was increased accordingly due to the influence of transfacetopedicular screw, especially under left axial rotation. However, the breakage risk of screws remained lower under rotation controlled properly. For stepping down the risk of pedicle screws fatigue breakage, the axial rotation after three kinds of fixation based on transforaminal lumbar fusion should be restrict severely, especially the axial rotation on the side that facet joint was destroyed.