Biomechanical Evaluation Of Lumbar Spondylolysis Repair With Various Fixation Options:A Finite Element Analysis

[Objective] This study was designed to compare the biomechanical properties of lumbar spondylolysis repairs using different fixation methods by using threedimensional finite element analysis.[Methods] Five finite element models(A,B,C,D,and E)of L4-S1 vertebral body were reconstructed by CT images of a male patient(A: intact model;B: spondylolysis model;C: spondylolysis model with intrasegmental direct fixation by Buck screw;D:spondylolysis model with intersegmental indirect fixation by pedicle screw system;E:spondylolysis model with hybrid internal fixation).L5-S1 level was defined as the operative level.After the intact model was verified,six physiological motion states were simulated by applying 500 N concentrated force and 10 Nm torque on the upper surface of L4.The biomechanical properties of the three different internal fixation methods were evaluated by comparing the range of motion(ROM),maximum stress,and maximum displacement.[Results] Compared with spondylolysis model B,the ROM and maximum displacement of intrasegmental internal fixation model C,intersegmental pedicle screw internal fixation model D,and mixed internal fixation model E decreased.The maximum stress on L5/S1 disc in intact model A,spondylolysis model B,and the intrasegmental internal fixation model C was much higher than in intersegmental pedicle screw internal fixation model D and mixed internal fixation model E under extension and lateral bending conditions.Under axial rotation and lateral bending conditions,the maximum stress of interarticular muscle and internal fixation system in spondylolysis model B and intrasegmental internal fixation model C was significantly higher than that in intersegmental pedicle screw internal fixation model D and the mixed internal fixation model E.In contrast to spondylolysis model with the intersegmental pedicle screw internal fixation model D,the mixed internal fixation model E was distributed in two internal fixation systems.[Conclusion] In several mechanical comparisons,hybrid fixation had better biomechanical properties than other fixation methods.The experimental results show that hybrid fixation can stabilize the isthmus and reduce intervertebral disc stress,which making it the preferred treatment for lumbar spondylolysis.