Analysis And Study Of Biomechanics After OLIF By Finite Element Method

Objictive Among the surgical methods for lumbar degenerative diseases,oblique lumbar interbody fusion(OLIF)through lateral anterior peritoneal approach has been gradually recognized by spinal surgeons for its fewer complications and better curative effect.In this study,three-dimensional models simulating different OLIF surgical methods were established by finite element method,and OLIF post-operative fusion was performed by finite element method.The stability of the syndesmosis and adjacent segments were compared,and the stress changes of fusion cage,fixator and lumbar spine structures after different OLIF operations and their relationships were explored,which provided biomechanical theoretical basis for improving the clinical efficacy of OLIF operations.Methods A normal adult male volunteer was selected,and the history of spinal diseases and traumatic diseases were excluded.The volunteers were scanned by CT in L2-5 segment of the lumbar spine with the approval and signature of the relevant informed consent form by the ethical committee.The CT images were imported into Mimics 17.0 software in Dicom format.The lumbar spine images of CT scanning were extracted by mimics software,and the external lumbar spine of L2-5 was obtained.The three-dimensional contour data of L2-5 lumbar spine are imported into Geomagic software,and then the three-dimensional solid model of L2-5 lumbar spine is formed by grinding,smoothing,surface editing and gridding with the software.Solid Works drawing software was used to draw the shape of screw and intervertebral fusion cage according to the engineering size and assemble them separately.The screw and the three-dimensional model of the intervertebral fusion cage were put into the lumbar spine model in Solid Works,and the corresponding position was adjusted.Three groups of lumbar spine models were established: normal adult male lumbar spine model(group A),simple implantation of Cage model after OLIF(group B)and post-OLIF(Cage + screw)model(group C).The material attributes of each part are quoted from literature reports.Then three groups of models are introduced into Ansys to simulate six motion states after applying constraints and loads.The stability of each part of the lumbar spine after OLIF and its influence on adjacent segment degeneration are analyzed and compared.At the same time,the stress changes and distributions of the important structures of the lumbar spine in the fusion cage,internal fixation device and operation area are measured and analyzed.Results The model established in this experiment was verified and compared with the literature,which met the requirements of model validation,and three groups of finite element models were successfully established and studied.The number of tetrahedron elements in group A is 127796,the number of nodes is 310286,the number of tetrahedrons in group B is 250825,the number of nodes is 444842,the number of nodes in group C is 154358,and the number of nodes is 301615.Under six loading conditions,the mobility of group B and group C models L2-3 and L3-4 was significantly lower than that of the normal model,but there was little difference between group B and group C.Compared with group B model,the equivalent stress of Cage in group C model was significantly reduced under six working conditions.When the three models were extended backward,the stress of lumbar facet joint under operative segment in group B increased significantly compared with group A model.Compared with group B and C,the stress of the upper and lower endplates of fusion segments increased significantly,while the stress of adjacent endplates did not change significantly,while the stress of adjacent endplates in group B and C did not increase significantly.Conclusion Both OLIF can achieve good stability after operation.Local stress concentration occurs in the canine teeth contacted with the vertebral body when using the fusion alone,and the stress of the facet joints below the fusion segment increases,suggesting that the degeneration of the facet joint may be accelerated.After the combined use of nail and rod internal fixation,the nail and rod will share part of the fusion and reduce the load of the fusion device,which will significantly reduce the occurrence of long-term complications such as the sinking and displacement of the fusion device.In addition,there was no significant increase in stress on adjacent segments after OLIF,suggesting that OLIF does not have a significant impact on adjacent segment degeneration.