Finite Element Analysis Of Dynamic Cervical Implant And Cervical Total Spondylectomy

Total spondylectomy is recognized as one of the effective methods for treating spinal tumors,can significantly reduce the risk of local recurrence.Internal fixation devices are needed to provide adequate mechanical strength and stability of the reconstruction segment because of the procedure leads to complete transaction of the cervical spine.Dynamic cervical implant is a U-shaped structure of cervical non-fusion implant device,It provides dynamic stability of the cervical spine,has the advantages of retaining the activity of the operation section.Research on the impact of the stability and the biomechanical properties of the cervical spine of internal fixation methods after total spondylectomy and dynamic stability after implantation has important clinical value,have become the focus of research and analysis.The three dimensional finite element model of the human lower cervical spine C_3⁷motion segments was established based on CT images and combined with image processing software.The nondestructive model consists of vertebral cortical bone,cancellous bone,arch,annulus,nucleus,collagen fibers,endplate,five major ligaments and cervical facet joints.On the basis of the non-destructive model,C₅ cervical segments and connected tissues include annulus,nucleus,endplate and ligaments were removed,the internal fixation devices include plate,titanium mesh and pedical screw were implanted in the model,two fixed finite element models after the whole resection of C₅ were established:?1?Reconstructed vertebral with Titanium mesh and anterior fixation with plates and posterior fixation with single segment pedicle screw,?2?Reconstructed vertebral with Titanium mesh and anterior fixation with plates and posterior fixation with single segment pedicle screw.On the basis of the non-destructive model,the C_5/6 segment of the disc and its anterior attached ligament and other tissues were resected,and two kinds of disc degeneration models were established:?1?finite element model of C_5/6 segment reconstructed with dynamic cervical implant through anterior approach,?2?finite element model of C_5/6 segment reconstructed with dynamic cervical implant through anterior approach.To compare and investigate the range of motion and the mechanical characteristics of implanted devices of each cervical segment under flexion,extension,lateral bending and axial rotation working conditions.The results showed that the range of motion of the non-destructive cervical spine C_3⁷ under four cases were consistent with the conclusions of previous studies in vitro experiments and finite element analysis of other people,verified the reliability of the model.ROM of the reconstruction segments of two fixed models after total spondylectomy of C₅ were greatly reduced by over 83%as compare to that of the intact model,stability of the reconstruction section segment improved significantly.Adjacent segments of TM+AP+SPS model had a great compensatory activity,Stress of the titanium mesh of TM+AP+SPS model was focused on the compression side,while Stress of the titanium mesh of TM+AP+SPS model was focused on the rear.Stress of the pedicle screw of TM+AP+SPS model and TM+AP+DPS model were all concentrated in the root of the screw and the pedicle of the cervical spine.From the stability considerations,the stability of cervical spine was better in TM+AP+DPS model.Comparison results of two models of Dynamic cervical implant stabilization and interbody fusion of the cervical C_5/6 segment degeneration treatment showed that,ROM of the surgical segment in DCI group was preserved better,can maintain normal physiological activities of cervical spine.ROM of the surgical segment after fusion surgery was lost 86%⁹1%,ROM of adjacent segments increased significantly,DCI surgery has smaller influence on cervical ROM and stress,and is more consistent with the biomechanical requirements of the cervical spine.The stress of DCI model were all concentrated on the"U-shaped"bottom under six working conditions,provides the reference and theoretical basis for selection of operation scheme and optimization of surgical instruments.