Objective:To compare the clinical efficacy and complications of combined anterior and posterior approach and simple posterior release reduction and internal fixation in the treatment of basilar invagination (BI) with irreducible atlantoaxial dislocation (IAAD) .Methods:The medical records of 47 patients with basilar invaginationdepression complicated with refractory atlantoaxial dislocation who received surgical treatment from July 2000 to December 2017 were retrospectively analyzed. The patients were divided into anterior and posterior combined approach group (23 cases) and posterior approach group (24 cases). Key observation indicators include: Chamberlain line (CL), Wackenheim line (WL), McGae line (ML), atlantodens interval (ADI), cervicomedullary angle (CMA), clivus-canal angle (CCA), JOA scores (Japanese Orthopedic Association, JOA) and Ranawat grade.Results:The average follow-up was 48.7±31.2 months in the A-P group and 44.4±33.4 months in the P group. The average preoperative JOA score of the A-P group was 8.20±2.75 points and 14.98±1.05 points at the last follow-up, and the improvement rate was 77.35%±11.35%. The average preoperative JOA score of the P group was 8.06±2.52 points, and the last follow-up was 14.71±0.62 points, and the improvement rate was 74.38%±10.52%. There was no statistically significant difference between the two groups in JOA score ( t=0.877, P=0.262) and improvement rate ( t=1.478, P=0.206) at the last follow-up. The preoperative CL, WL, ML, ADI, CMA and CCA angles of the A-P group were 13.12±5.76 mm, 6.94±3.55 mm, 7.04±4.57 mm, 9.75±2.06 mm, 110.85°±13.6°, 95.32°±18.3°, respectively. The last follow-up was 1.68±2.53 mm, -2.76±2.26 mm,-1.52±2.43 mm, 1.12±1.55 mm, 149.26°±12.6°, and 141.42°±13.7°, respectively, with statistically significant differences from preoperative. The preoperative CL, WL, ML, ADI, CMA and CCA angles of P group were 12.52±5.17 mm, 6.59±3.04 mm, 6.94±4.32 mm, 9.88±1.93 mm, 115.35°±12.4°, 97.25°±16.4°, respectively. The results of the last follow-up were 2.00±3.67 mm, -3.06±1.85 mm, -1.76±2.88 mm, 1.17±1.18 mm, 146.76°±11.4° and 137.56°±10.4°, respectively, which were statistically significant compared with the preoperative results. There was no significant difference between the two groups in preoperative and final follow-up. The average bone graft fusion time of the A-P group was 9.2±4.9 months, and the average bone graft fusion time of the P group was 9.5±4.7 months. There was no statistically significant difference in the bone graft fusion time between the two groups ( t=0.547, P=0.382). Postoperative complications occurred in a total of 8 cases in the two groups, including 6 cases (21.7%) in the combined approach group and 2 cases (8.3%) in the posterior approach group. The incidence of complications in the posterior approach group was significantly lower than that in the combined approach group. Conclusion:The clinical and imaging results of the treatment of basilar depression with atlantoaxial dislocation by one-stage posterior release reduction and internal fixation are basically the same as those obtained by the anterior and posterior combined approach, but the complication rate of the posterior approach is significantly lower than that of the anterior and posterior combined approach.