A Comparative Study On The Efficacy Of Two Axial Internal Fixation Systems In The Treatment Of Basilar Invagination Combined With Atlantoaxial Dislocation

Objective:By comparing the efficacy and prognosis of C₂lateral laminar screw+contralateral pedicle screw internal fixation system and C₂bilateral pedicle screw internal fixation system in the treatment of basilar invagination combined with atlantoaxial dislocation,to explore the C₂lateral laminar screw+Clinical application value of contralateral pedicle screw internal fixation system.Through the external pull-out force test,the biomechanical differences between C₂pedicle screw and laminar screw were compared,and an attempt was made to provide a biomechanical basis for the choice of clinical screw placement.Methods:The patients with skull base depression and atlantoaxial dislocation who were admitted to the Department of Neurosurgery,Affiliated Hospital of Guizhou Medical University from 2016 to September 2021 were retrospectively collected.After excluding patients with severe osteoporosis,45 cases were enrolled and completed the follow-up,and 2 cases were lost to follow-up.According to the presence or absence of abnormal C₂unilateral vertebral artery course or the contraindication of pedicle screw placement such as slender axial pedicle,the patients were divided into two groups:A and B.Group A（32 cases）:the patients had no contraindication to pedicle screw placement,and C₂bilateral pedicle screws were placed;group B（13 cases）:patients had unilateral pedicle screw placement contraindications,and they were placed C₂lamina screw on one side+pedicle screw on the opposite side.After C₂screw placement,patients with atlanto-occipital fusion deformity were treated with C₂screw+occipital plate internal fixation system,and the axial lamina and the outer cortical bone below the occipital plate were removed with a drill,and a bone graft bed was prepared for implantation.bone.For patients with normal atlanto-axial fusion,the outer cortical bone of the atlantoaxial lamina was removed with a drill,and a bone graft bed was prepared for bone grafting.The cervical collar was strictly worn for more than 3 months postoperatively.The two groups of patients were followed up,and the follow-up time was 1 week after operation,3 months after operation,and the last follow-up after operation（the last follow-up time was more than 6 months）.The clinical data of the two groups of patients were compared,including gender,age,JOA score before and after surgery,JOA improvement rate,ADI（atlantoaxial gap）,and the distance from the tip of the odontoid to the Qian’s line（DOCL）.),medulla oblongata angle,bone graft fusion and other imaging data.All data were statistically analyzed by SPSS 22.0.If the samples conformed to normal distribution,independent samples t test was used.For non-normality,independent samples rank sum test was used.The count data were compared by chi-square test.P<0.05 was considered statistically significant.Axis unicortical pedicle screw and unicortical laminar screw fixation were performed on 6 human axial specimens,and the maximum screw pullout force was tested and statistically analyzed.Results:In the retrospective study,45 patients were followed up,and all of them successfully completed the operation.One week after the operation,the reduction of the atlantoaxial joint had a good effect.The JOA scores of the two groups of patients at 1 week after operation and at the last follow-up were significantly different from those before operation（P<0.05）,which proved that both internal fixation systems were safe and reliable,and the neurological dysfunction was improved well.There were statistically significant differences in the two groups of patients at 1 week after operation and at the last follow-up in terms of medullary cervical spinal angle,ADI,and the distance from the tip of the odontoid process to Qian’s line（DOCL）compared with those before operation（P<0.05）.,which proves that the reduction effect of the two internal fixation systems is good,and the cervical medullary angle continues to increase.There was no significant difference in the JOA improvement rate between the two groups at 1 week after operation,3 months after operation and at the last follow-up（P>0.05）,suggesting that two different internal fixation systems have different effects on postoperative neurological improvement.At the last follow-up after operation,all patients in group A had bone graft fusion,and 1 patient in group B had poor bone graft fusion,but there was no significant difference in the rate of bone graft fusion between the two groups（P>0.05）.In the in vitro pull-out force study,the average maximum pull-out force of unicortical axis pedicle screws was 646.54±229.00N,and the average maximum pull-out force of unicortical axis pedicle screws was 383.25±169.20N;pedicle screws The maximum pull-out force was greater than that of laminar screws,and the difference was statistically significant（P<0.05）.Conclusions:The posterior internal fixation system composed of the two axial screw placement methods can achieve satisfactory clinical effects,effectively improve the medulla oblongata angle,and adequately decompress the medulla oblongata and cervical spinal cord.C2 bilateral pedicle screw internal fixation system has good long-term reduction effect and improved neurological function,and is the preferred internal fixation method for posterior surgery.For patients with contraindications to C2 pedicle screw placement,the C2 lateral lamina screw+contralateral pedicle screw internal fixation system can also provide a good reduction effect and effectively improve the patient’s neurological dysfunction.It is a feasible method.alternative plan.