Risk Factors for Radiologic Subaxial Cervical Pathology After C1-2 Posterior Fusion

Background/Objectives: Atlantoaxial posterior fusion has unique characteristics, and it is anticipated that adjacent segment degenerative changes following fusion surgery may present distinctive findings. This study aims to analyze the risk factors for degenerative changes in subaxial levels following the increasingly common atlantoaxial posterior fusion procedure. Methods: A total of 58 patients (19 males, 39 females) who had neutral, flexion, and extension plain lateral radiographs taken and a follow-up record of approximately two years post-surgery were included in the final study cohort. The study analyzed surgical methods, patient demographics, hospitalization-related factors, visual analog scale (VAS) for neck pain, and radiologic parameters. Patients were classified into the radiologic subaxial pathology (RSP) group (n = 34) and the non-RSP group (n = 24) using several radiologic indicators of spinal instability or arthritic changes, and the risk factors for RSP were analyzed. Results: The RSP group showed a significantly higher proportion of females and prevalence of rheumatoid arthritis (RA). At 3 months postoperatively, the C1-7 sagittal vertical axis (SVA) was significantly lower in the RSP group. Multivariate regression analysis using significant variables (p < 0.05) such as sex, RA and 3-month C1-7 SVA showed that RA and 3-month C1-7 SVA were significantly associated with RSP. Among radiologic parameters related to surgery, multivariate analysis identified 3-month C1-7 SVA as the sole risk factor for RSP. To explore its correlation with other radiologic parameters at 3 months postoperatively, linear logistic regression analysis was conducted. Significant positive correlations were observed with the C1-2 Cobb angle. Conclusions: This study identified RA and C1-7 SVA as the most significant risk factors for RSP in atlantoaixal posterior fusion.