Three-dimensional Finite Element Analysis Of Anterior/Posterior Articular Mass Screw Of C2 And Preliminary Clinical Application Of Posterior Articular Mass Screw Of C2

Objective:1.To establish a three-dimensional finite element model of normal total cervical vertebra and an instability model of the upper cervical spine,then verify the validity of the two models;2.Five different internal fixation methods are loaded on the instability model,including two anterior approaches and three posterior approaches,and then the finite element analysis is carried out;3.Study on the clinical effect of articular mass screw of C2.Method:Select a volunteer and obtain CT images of his cervical vertebrae,and construct a three-dimensional finite element model of normal whole cervical vertebra by using finite element software based on CT data,and verify the validity of the model.Then,on the basis of the normal model,the upper cervical instability model was established by removing transverse ligament tissue and its validity was verified.Finally,five different internal fixation methods were loaded on the instability model.Among them,there are two kinds of anterior approach:TARP operation combined with different anterior screws of C2(A)bilateral transoral articular mass screws of C2 group and(B)bilateral transoral reverse pedicle screws of C2 group.Three kinds of posterior approach:Atlas pedicle screws supplemented with different axial posterior screws(C)bilateral articular mass screws of C2 group,(D)bilateral pedicle screws of C2 group(E)bilateral lamina screws of C2 group.The range of motion(ROM)and stress of C1-C2 under different working conditions such as flexion and extension,lateral bending and axial rotation were obtained by finite element calculation.A clinical case of atlantoaxial dislocation treated with posterior articular mass screw of C2 as a substitute for posterior pedicle screw fixation was analyzed retrospectively.A 26-year-old male patient diagnosed atlantoaxial dislocation was unable to place nails because of the narrow bilateral axial pedicle.The operation was performed with posterior axial facet screw combined with bilateral atlas pedicle screw fixation and fusion,and satisfactory results were obtained.Result:1.The three-dimensional finite element model of normal whole cervical vertebra and the instability model of upper cervical vertebra established in this study are consistent with the actual anatomical structure of cervical vertebra,has good geometric similarity and has been verified,which can be used for further biomechanical research.2.There was no significant difference in ROM value of C1-C2 segment between two different internal fixation models of anterior approach,and no significant difference in ROM value of C1-C2 segment of three different internal fixation models of posterior approach.3.The peak stress of the two internal fixation models of the anterior approach was different,group A>group B,while the peak stress of the three internal fixation models of the posterior approach was different,and the overall trend was group C>group E>group D.4.Clinical case study:the course of operation was smooth,postoperative CT showed that all screws were fixed in place,the position of nail path was good,and no abnormality was found.X-ray examination 8 months after operation showed that the atlantoaxial screw was fixed and the bone graft was fused,and no complications such as loosening and unnailing were found.Conclusion:1.The three-dimensional finite element model and instability model of normal whole cervical vertebra established in this study have good geometric similarity and have been verified.2.In TARP operation,both bilateral transoral articular mass screw of C2 and bilateral transoral reverse pedicle screw of C2 can significantly reduce the range of motion of C1-C2,there are no significant difference in biomechanical stability between them(P>0.05).In posterior cervical surgery,Cl pedicle screw fixation with articular mass screw or pedicle screw or lamina screw of C2 can provide reliable biomechanical stability,and there are no significant difference among them(P>0.05).3.Anterior/posterior articular mass screws of C2 are reliable and can be used as an alternative and complementary nail placement technique for anterior/posterior transoral pedicle screws of C2.The initial clinical application of posterior articular mass screw of C2 is satisfactory.