Correlation of Cervical Sagittal Alignment, C1-C2 Fixation Angle and Age of Spontaneous Atlantoaxial Dislocation, its Clinical Significance

The atlanto-occipital joint and atlantoaxial joint are considered to be the important functional parts of the human skull-cervical axis. Research has found that the rotation of the craniocervical spine mainly depends on the atlantoaxial joint. The normal atlantoaxial joint plane is too flat to maintain its stability, so it is prone to spontaneous atlantoaxial dislocation. At present, posterior atlantoaxial fusion surgery is widely used for the treatment of atlantoaxial dislocation. Previous studies retrospectively analyzed the relationship between SVA angle, C1-C2 angle, and C2-C7 angle, but due to limitations in analytical methods, the role of age as a potential modifier or confounding factor for these relationships has not been fully studied.In this study, we found that the preoperative C2-C7 angle was positively correlated with the postoperative C2-C7 angle and preoperative C2-C7 SVA . Postoperative C2-C7 SVA was correlated with NDI and VAS. At the same time, with increasing age, patients' clinical manifestations become more pronounced and discomfort significantly increases. And based on the random forest regression model, we used age, C1-C2 angle, and C2-C7 SVA as predictive variables to construct predictive models for postoperative C1-C2 and C2-C7. Our study reveals that middle-aged and elderly patients with spontaneous atlantoaxial dislocation experience more severe pain and discomfort. Posterior surgery for this condition normalizes cervical spine curvature by increasing the C1-C2 angle and decreasing the C2-C7 angle, thus improving clinical symptoms. Proper C1-C2 angle fixation during surgery is crucial for postoperative correction. Restoring C2-C7 is more effective than C1-C2 in reducing pain. Machine learning analysis shows that age affects postoperative C1-C2 angle and C2-C7 SVA, but the relationship is not linear. Therefore, age should not be used as a simple linear predictor in surgical planning.