The Anatomic And Radiographic Study Of Transoral Atlantoaxial Cage And Internal Fixation System

BackgroundUpper cervical spine deformity is a common disease,often causing nerve damage.Surgery is an effective way to prevent further deterioration of neurological function.The key treatment is full decompression and reliable internal fixation.For patients with irreducible atlantoaxial dislocation,the current mainstream surgical option is one-stage anterior release and/or odontotomy with posterior occipitocervical fusion.,However,repositioning may cause fatal injury to the patient and surgical trauma can't be neglected.In recent years,the technology for the treatment of upper cervical spine deformity continues to develop,providing patients with better surgical options.We confirmed the feasibility of the transoral atlantoaxial distraction in the early clinical work,so we will design an integrative system of transoral atlantoaxial cage and internal fixation to reduce the difficulty of operation and surgery-related complications,and improve long-term efficacy.ObjectiveCollecting the imaging data and clinical outcome of patients with basilar invagination and irreducible atlantoaxial dislocation treated by Transoral atlantoaxial reduction internal fixation provides the theoretical basis for the design of integrative system of transoral atlantoaxial cage and internal fixation.Through the atlantoaxial anatomy and imaging measurement of Chinese adult specimens,we set the foundation for the design of integrative system of transoral atlantoaxial cage and internal fixation.MethodsPart ?We collected the imaging data and clinical evaluation of 22 patients with basilar invagination and irreducible atlantoaxial dislocation in the previous period.Imaging data include:(1)O-C2 angle:the angle of the McGregor line and the inferior edge of the axis of the vertebral body measured by lateral cervical X-ray before and after surgery;(2)dO-C2 angle:dO-C2 angle = preoperative O-C2 angle-postoperative O-C2 angle;(3)dCL:dCL = preoperative CL-postoperative CL(CL is defined as vertical distance from the maxillary odontoid to the Chamberlian line on the sagittal plane of the CT);(4)atlas-dens interval(ADI).Clinical evaluation included:(1)neurological improvement rate =(postoperative JOA-preoperative JOA)/(17-preoperative JOA)× 100%.Twenty-two patients were divided into group A(neurofunctional improvement<50%)and group B(neurological improvement ?50%)according to the rate of neurological improvement.Part ?48 Chinese adult specimens and 50 atlantoaxial CT three-dimensional reconstructions were measured.The relevant parameters are as follows:?the sagittal diameter of C1 lateral mass articulation;?the transverse diameter of C1 lateral mass articulation;?the length of atlas screw;?atlas screw insertion angle:atlas screw angle side to head(al),atlas screw insertion outside angle(?2);?the sagittal diameter of C2 lateral mass articulation;?the transverse diameter of C2 lateral mass articulation;?the length of axis screw;?xis screw insertion angle:atlas screw insertion outside angle(?1),atlas screw angle side to tail(?2);?atlantoaxial lateral mass joint space.ResultsPart ?Group A included 5 patients and group B,17 patients,all patients with clinical symptoms were improved.There was no significant difference in ADI,CL,dCL,O-C2 angle and dO-C2 angle between group A and group B(P>0.05).The mean preoperative symptom treatment interval of group A was 106 ± 68 months and group B 45 ± 47 months,the difference was statistically significant(P<0.05).1 patient underwent MRI examination showed that there are still persistent compression of the brain stem,the second-stage of transoral odontotomy with posterior fixation was performed,the symptoms were not significantly alleviated.No internal fixation failure,incision infection and other complications were foundPart ?The entry point of the atlas is 2mm above the junction point of the lateral mass of the atlas and anterior arch of the atlas.The exit point of the atlas is the crossing of the centerline of atlas pedicle and the posterior arch of atlas.The entry point of axis is 2mm below the junction point of the articular surface of axial lateral mass and the base of the dens.The exit point of axis is the junction point of axis pedicle centerline and the vertebral laminae.The anatomical measurement outcome of Atlantoaxial specimen was as follows:the sagittal diameter of C1 lateral mass articulation was 17.12±1.29mm,the transverse diameter of C1 lateral mass articulation was 15.76±1.16 mm,the length of atlas screw was 27.51±1.85 mm,the sagittal diameter of C2 lateral mass articulation 17.46±1.55 mm,the transverse diameter of C2 lateral mass articulation 15.79±1.11 mm,the length of axis screw 28.24±1.59 mm.The radiological measurement outcome of imagines of atlantoaxial three-dimensional reconstruction were as follows:the sagittal diameter of C1 lateral mass articulation was 17.34±1.26mm,the transverse diameter of C1 lateral mass articulation was 15.95±1.15mm,the length of atlas screw was 27.74±1.84mm.Atlas screw insertion outside angle was 12.67±0.66 degree,and atlas screw angle side to head was 13.42±1.00 degree.The sagittal diameter of C2 lateral mass articulation 17.71 ± 1.52 mm,the transverse diameter of C2 lateral mass articulation 16.02±1.10 mm,the length of axis screw 28.45±1.57mm.Axis screw angle side to tail was 15.40±0.31 degree,and axis screw insertion outside angle was 12.53±0.29 degree.The anterior space height atlantoaxial lateral mass joint was 3.24±0.53mm,and posterior space height atlantoaxial lateral mass joint was 2.60±0.53mm.ConclusionsAtlantoaxial joint distraction technique for treatment of basilar invagination with irreducible atlantoaxial dislocation is effective.Atlantoaxial joint distraction technique without odontotomy can effectively recede the odontoid process,reduce the atlantoaxial dislocation and decompress the spinal cord.The data from anatomical and radiological measurement confirmed the feasibility of the integrative system of transoral atlantoaxial cage and internal fixation.