Fig. 3

The prevalence of cervical spine instability comprising AAS, VS, and SAS at baseline, > 5-year follow-up, and > 10-year follow-up in 162 consecutively followed patients. To simplify, VS combined with AAS was categorized as VS. The chi-squared test was used for the comparison. AAS atlantoaxial subluxation, VS vertical subluxation, SAS subaxial subluxation.