| Objective:(1)Utilize modeling software to generate the finite element model of the L4-S1 segment,as well as the L4-S1 segment afflicted with L5 bilateral spondylolysis.(2)Develop three internal fixation system models using computer-aided design software and simulate surgery for L5 bilateral spondylolysis.(3)Investigate the biomechanical properties of the five groups of models.(4)Assess the advantages of different internal fixation techniques in the management of lumbar spondylolysis.Methods:Recruit a healthy young male soldier as a volunteer for thin-layer 3D CT scanning of the lumbosacral vertebrae and save the scan data in the DICOM format.Use Mimics Research 21.0software to initially establish a three-dimensional geometric model and save it in STL+ format.Refine the model through Geomagic Wrap 21.0 software,smoothing,reducing noise,and correcting errors to simulate a NURBS surface solid model saved in STEP format.Using Solidworks 21.0 software,assemble the model,construct vertebral body attachments and internal fixation,simulate L5 bilateral spondylolysis and surgical repair of spondylolysis,and finally generate a three-dimensional model of the normal L4-S1 segment,L4-S1 segment with L5 bilateral spondylolysis,and three repair techniques: Buck screw,pedicle screw-rod-plate hook,and pedicle screw "U" rod,denoted as A,B,C,D,and E,respectively.Analyse the biomechanics of the five groups of models under the same loading conditions(axial compression,flexion,extension,left bending,and left rotation)using Ansys Workbench 17.0software,and compare the resulting biomechanical differences between the different models.Result:(1)The data obtained from the normal model in this experiment is consistent with the previous research data,and we have successfully developed an effective three-dimensional finite element model for the L4-S1 segment.(2)After bilateral spondylolysis at L5,the total range of motion(ROM)for both the L4-S1 and L5/S1 segments increased under all load conditions,with the greatest increase observed during left bending and rotation.The total ROM and ROM for each segment of the three groups of internal fixation models are comparable to those of the normal model.(3)The total average maximum displacement of model B differs significantly from that of the other four models in five motion states(P<0.05).There was no statistically significant difference between the average maximum displacement of the three groups of internal fixation models and model A during axial compression and extension(P>0.05).The average maximum displacement of model C and model D during left rotation and model A and model C during left bending is smaller than that of model E,and there are significant differences between them(P<0.05).(4)The mean maximum stress of the cancellous bone implanted in the three groups of internal fixation models exhibited statistically significant differences in each motion state(P<0.05).During extension,the stress was lowest in model D,followed by model E and model C.For the other four motion states,the stress was lowest in model C,followed by model D and model E.(5)The mean maximum displacement of the isthmus in model B was significantly higher than that in the other four groups of models under all loading conditions,with a statistically significant difference(P<0.05).The mean maximum displacement of the isthmus in the three groups of internal fixation models was smallest in model D under all motion states except axial compression.The displacement in model C was greater than that in model E under axial compression and forward flexion,while the displacement in model C was less than that in model E under other states.(6)The mean maximum stress of internal fixation in the three groups did not exhibit statistical differences in axial compression(P>0.05).However,in left bending and left rotation,the stress was lowest in model E,followed by model D and model C.In forward bending,the stress was lowest in model E,followed by model C and model D.In backward extension,the stress was highest in model C,followed by models D and E,with a statistically significant difference between them(P<0.05).There was no statistical difference in stress between models D and E in backward extension(P>0.05).(7)The maximum stress of the L4/5 intervertebral disc in the five groups of models did not significantly change in each motion state.However,the maximum stress of the L5/S1 intervertebral disc exhibited a statistically significant difference between the five groups(P<0.05).The stress was highest in model B,followed by models E,A,C and D.There was no significant difference in stress between models A,C,and D(P>0.05).Conclusion:(1)A highly effective three-dimensional finite element model of the L4-S1 segment was successfully obtained in this study.(2)Spondylolysis leads to significant alterations in the biomechanical conduction of the spine,resulting in pronounced instability.Furthermore,the intervertebral disc of the affected segment may undergo degeneration during physiological movement.(3)All three groups of internal fixation models significantly improved the stability of the lumbar spine.However,it was found that the isthmus and overall stability of the pedicle screw "U" rod model were weaker when compared to the pedicle screw-rod-plate hook and Buck screw systems.(4)In the "U" rod pedicle screw model,the average maximum stress of the L5/S1 intervertebral disc is higher compared to that of the pedicle screw-rod-lamina hook and Buck screw system.Consequently,the possibility of degeneration of the intervertebral disc of the lesion segment is greater when using the pedicle screw "U" rod system to repair isthmic fissure.(5)The average maximum stress of the Buck screw system in all motion states is higher than that of the pedicle screw "U" rod and pedicle screw-rod-lamina hook system.Therefore,it can be considered that the risk of internal fixation fracture after surgery is higher with the Buck screw system compared to the other two systems.(6)Taking into account the biomechanical characteristics of the three internal fixation methods,this study concluded that the pedicle screw-rod-lamina hook system exhibits superior biomechanical properties. |
PDF Full Text Request