Biomechanical Evaluation Of Screw Pull-out Strength On Axis Of Anterior Transoralpharyngeal Atlantoaxial Reduction Plate And Clinical Application

BackgroundAltantoaxial dislocation is mostly caused by craniocervical junction injury,inflammation,congenital malformations,tumor and other factors.The incidence of altantoaxial dislocation is low,but it has high morbidity and mortality.Transoral direct access to the craniocervical junction of the lesion and the injury site, directly past way to lift the oppression of the ventral cervical spinal cord.The traditional transoral approach can decompress the oppression of the ventral cervical spinal cord and simultaneously fix altantoaxial from back.To achieve the reduction of intraoperative real-time directly from the front of the atlantoaxial fixation, so that decompression, reduction and fixation time to complete, we designed transoralpharyngeal atlantoaxial reduction plate (TARP), to the related biomechanics and anatomy study experienced TARPⅠ,Ⅱgeneration of development, in the past TARPⅠ,Ⅱbehalf despite his good biomechanics, but clinically still screw loose, shifting bit, especially for the loose screw axis, the clinical axis screw loosening rate isabout 10%.To meet the atlantoaxial fixation after reduction requirements, TARP system remains constant improvement and development, and bio-mechanics research and stress distribution to clinical applications of the TARP system must be provided.Objective:To evaluate the transoral screw pull-out strength on C2 of transoralpharyngeal atlantoaxial reduction plate(TARP) and TARP-Ⅲsystem's application and efficacy in the treatment of irreducible atlantoaxial dislocation.Method:1.Six fresh C1,C2 spine specimens(totally 12 cases including both sides) were designed to compare screw pull-out strength of C1 and C2.C1 screw was impla nted into the lateral mass,C2 screw was separately implanted into pedicle,vertebrae and articular process underneath,and the pull-out strength was tested and compared.Statistical processing:SPSS 13.0 statistical software was used for data processing and statistical analysis. Measurement data were recorded by mean±standard deviation(X±s).Using completely randomized design analysis of variance(One-way ANOVA) and SNK pairwise comparison test for statistical analysis,,with P<0.05 for significant difference.2.21 cases of unreducible atlantoaxial dislocation underwent reduction and fixation with TARP system were followed up for 6-18 months with an average of 12 months.C2 screw was separately implanted into pedicleand articular process underneath.Follow-up observation of atlantoaxial fusion, atlantoaxial stability, with or without internal fixation loosening, with or without postoperative infection to occur.Result:1.There are no statistically significa nt difference between screw pull-out strength of C1 latera 1 mass screw (546.45±85.07N) and C2 pedicle screw (593.14±97.77N), however,that of C1 lateral mass screw is stronger than C2 vertebrae screw and C2 screw underneath articular process.The pull-out strength of C2 screw underneath articular process is stronger than C2 vertebrae screw.2.All cases of atlantoaxial dislocation were treated by the TARP surgery experienced anatomic atlas, decompression of the spinal cord, rigid fixation, good fusion after three months. The clinical results are satisfactory.Conclusion:Experimentally,pedicle screw fixation transoral approach to C2 pedicle and C2 articular process underneath of TARP is strong and safe.TARP system of axis with anterior pedicle screw better than under the fixed axis vertebraeand the atlas lateral mass screw fixation. Axis screws with anterior pedicle screw fixation of TARP system is safe, and the pull-out strength was significantly better than vertebral facet screws,so anterior pedicle screw fixation on axis is the first choice for TARP system; atlantoaxial facet screw fixation is better than that of vertebral axis screw, and reduces the risk of spinal cord injury, for irreducible atlantoaxial dislocation axis is not appropriate with anterior pedicle screw screw, atlantoaxial facet screw fixation can be used as first choice under the supplementary scheme.In short, TARP system uses pedicle screws or facet joint screw fixation for the whereabouts of the atlas lateral mass screw fixation, which is more secure and reliable, can significantly reduce the risk of clinical screw loosening and confirm reset fixed atlantoaxial dislocation, for the TARP-Ⅲclinical application on behalf of the plate provides a biomechanical basis.TARP-Ⅲgeneration systems used in clinical for the stability after the atlantoaxial reduction, reducing spinal cord compression, promoting fusion rate and reducing the postoperative screw loosening were positive.