目的　建立腰骶椎椎间融合椎弓根钉内固定的有限元力学模型，并对椎弓根螺钉和融合器的应力分布进行生物力学评价。  方法　通过CT扫描、Mimics三维重建、Freeform表面处理和Ansys前处理等方法建立正常腰骶椎L4~S1节段有限元模型，并据此建立去除L5~S1椎间盘后椎弓根钉后路固定加椎间融合模型固定。并对模型进行前屈、后伸、侧弯和旋转加载分析，观察模型的钉棒结构、Cage在4种加载状态下的应力分布情况。  结果　前屈、后伸、侧弯和旋转加载时椎弓根钉应力主要集中在钉的尾部和钉棒交界处。 Cage在旋转加载时应力集中在中部，在其它三种状态下的应力集中在前缘。在4种加载状态下棒钉结构和椎间融合器的最大应力值分别如下，前屈：2.96×107  N/m2 ，  5.65×106 N/m2 ； 后伸：2.98×107 N/m2 ， 6.08×106 N/m2；侧弯：3.06×107 N/m2 ，9.71×106 N/m2；旋转：2.96×107 N/m2， 1.00×106 N/m2；    结论　本实验成功建立了L4~S1节段后路椎间融合内固定的有限元模型，模型加载后的内固定应力分布符合临床观察，具有一定临床指导意义。

Objective    To develop a three-dimensional finite element model for posterior fusion surgery of L4~S1 and evaluate the stress distributions of the pedicle screw and cage.   Method    The finite element model of normal lumbosacral vertebral L4~S1 segments with removal of L5~S1 intervertebral disc was established through CT scan，three-dimensional reconstruction by using Mimics，surface treatment by using Freeform and analysis by using Ansys, respectively. The model was fixed by the posterior pedicle screws and intervertebral fusion. The model was analyzed under different conditions such as flexion，extension，bending and rotation under the same load.　Results　All the stress mostly concentrated on the screw tail and junction between the arch bar and the screw. The stress on the Cage was mainly located in the anterior part except under the condition of rotation, which is located at the middle. The peak stress on screw and cage are 2.96×107  N/m2 ，  5.65×106 N/m2  in flexion, 2.98×107 N/m2 ， 6.08×106 N/m2  in extension, 3.06×107 N/m2 ，9.71×106 N/m2 in bending, 2.96×107 N/m2， 1.00×106 N/m2 in rotation.　Conclusion　Three-dimensional finite element model of posterior fusion surgery of L4~S1 has been developed successfully and the stress distribution of pedicle screw and cage are close to clinical record, which can provide a significant guidance for clinical practice.