Optimization and finite element analysis of a safe screw pathway in bilateral lumbo-iliac fixation / 中华创伤骨科杂志

ABSTRACT

Objective:To analyze the biomechanical characteristics of bilateral lumbo-iliac fixation by finite element analysis after digital optimization of a safe screw pathway.Methods:Firstly, a healthy adult male volunteer was recruited for this study who underwent CT scanning of the lumbus and pelvis, with a slice thickness of 0.625 mm.The original data were imported into Mimics 16.0 software for 3D lumbar and pelvic reconstruction.At the same time, a geometric screw pathway and a free screw pathway were generated in the pedicles of L4 and L5 and ilium.Secondly, all 3D models were imported into Ansys 12 software to assemble a finite element model.The displacements and von Misses stress distribution were measured in the conditions of forward bending, backward extending, lateral bending to the left and right, and left and right rotations in the models of 2 kinds of pathway after gravity axial load of 500 N was applied.Results:The models of 2 different pathways were similar in comprehensive displacement and stress in the conditions of forward bending, lateral bending and backward extending, and in the maximum stress of the screw in the conditions of forward bending and lateral bending.However, the comprehensive displacement and stress in the condition of rotation and the stress of the screw in the conditions of backward extending and rotating in the model of geometric screw pathway were obviously smaller than those in the model of free screw pathway.The maximum pelvic stress was on the screw surface between 190 and 260 MPa, concentrated on the bending area of the 2 screws connecting the sacrum and vertebral body.The lumbar-iliac fixation model showed high com-pressive stiffness.The maximum von Misses stress appeared in the L4-L5 pedicle screw on the longitudinal rod.Under rotational loading, the upper longitudinal rod connecting the L4-L5 pedicle screw and the iliac bone screw bore the maximum stress.Conclusions:Our finite element analysis shows that double verte-bral bodies and long screw fixation are effective ways of iliolumbar fixation.The geometric screw path optimized by digital analysis exhibits better fatigue resistance, rotation resistance and overall stability.Internal lum-bo-iliac fixation can effectively share the stress of vertebral bodies.