Relationship between O-EA angle and lower cervical curvature in patients with anterior atlantoaxial dislocation before and after occipitocervical fusion

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To investigate the relationship between O-EA angle and lower cervical curvature in patients with anterior atlantoaxial dislocation undergoing occipitocervical fusion, and to analyze the effect of O-EA angle on lower cervical curvature. The clinical data of 61 patients with anterior atlantoaxial dislocation undergoing occipitocervical fusion who were admitted between April 2010 and July 2018 and met the selection criteria were retrospectively analyzed. There were 32 males and 29 females, with an age of 14-76 years (mean, 50.7 years). The fixed segment included 19 cases of C 0-C 2, 27 cases of C 0-C 3, 14 cases of C 0-C 4, and 1 case of C 0-C 5. The O-EA angle, C 2-7 Cobb angle, and T 1 tilt angle were measured before operation and at last follow-up. According to the O-EA angle measured at last follow-up, the patients were divided into <95° group (group A), 95°-105° group (group B), and >105° group (group C), and compared the differences of gender, age, fixed segment (short segment was at C 3 and above, long segment was beyond C 3), and C 2-7 Cobb angle. Correlation analysis between the O-EA angle and C 2-7 Cobb angle before operation and at last follow-up, as well as the changes of O-EA angle and C 2-7 Cobb angle between before operation and at last follow-up were analyzed. All 61 patients were followed up 12-24 months, with an average of 22.4 months. There was no significant difference in O-EA angle, C 2-7 Cobb angle, and T 1 tilt angle before operation and at last follow-up ( P>0.05). According to the last follow-up O-EA angle grouping, there were 14 cases in group A, 29 cases in group B, and 18 cases in group C. There was no significant difference in age, gender composition, and fixed segment composition among the three groups ( P>0.05); the differences in C 2-7 Cobb angles among the three groups were significant ( P<0.05), groups A, B, and C showed a gradually increasing trend. The O-EA angle was positively correlated with C 2-7 Cobb angle before operation and at last follow-up ( r=0.572, P=0.000; r=0.618, P=0.000); O-EA angle change at last follow-up was also positively correlated with C 2-7 Cobb change ( r=0.446, P=0.000). The O-EA angle of patients with anterior atlantoaxial dislocation is positively correlated with C 2-7 Cobb angle. Too large O-EA angle should be avoided during occipitocervical fixation, otherwise it may accelerate the degeneration of the lower cervical spine.