Abstract:

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.

Key words:  Finite element, Intervertebral fusion, Three-dimensional reconstruction, Pedicle screw