[Clinical application of a quantitative method of atlantoaxial reduction angle in basilar invagination]

Objectives: To investigate the clinical application effect of a quantitative method of atlantoaxial reduction angle in basilar invagination. Methods: A retrospective analysis of clinical and radiographic data was conducted of 38 patients with complicated atlantoaxial dislocation and basilar invagination admitted to the Department of Neurosurgery, First Affiliated Hospital of Chongqing Medical University from May 2020 to May 2022. There were 5 males and 33 females, aged (53.5±9.9) years (range: 38 to 80 years). All patients underwent C_1-2 interarticular fusion cage implantation+occipital-cervical fixation by pressing rob with the cantilever technique. The atlantoaxial reduction model of previous studies by our team was used to calculate the reduction angles before surgery. Then titanium rods of prebending angle were prepared according to the calculation before the operation. After that quantitative reduction of angle was performed during the operation. The paired t-test was used to compare the difference between the theoretical and actual reset value. Results: The theoretical reduction angle of all patients was (10.62±1.78)° (range: 6.40° to 13.20°), the actual reduction angle was (10.53±1.63)° (range: 6.70° to 13.30°) and there was no statistical difference between them (t=1.688, P=0.100). The theoretical posterior occipitocervical angle after the operation of all patients was (117.37±5.88)° (range: 107.00° to 133.00°), the actual posterior occipitocervical angle after the operation was (118.25±6.77)° (range: 105.40° to 135.80°) and there was no statistical difference between them (t=-0.737, P=0.466). The postoperative follow-up time of the patients was more than 6 months and the symptoms of all patients were relieved. All patients had satisfactory fusion between small joints without incision infection, internal fixation fracture, displacement, atlantoaxial redislocation, and other long-term complications. Conclusion: The quantitative method of atlantoaxial reduction angle in basilar invagination can calculate the theoretical reduction angle of the clivus axis angle and guide the preparation of the pre-bending titanium rod before surgery, so as to realize the quantification of the atlantoaxial reduction angle.