Objective. To analyze radiologic findings of cervical involvement in ankylosing spondylitis (AS) patients, determine its association with structural severity and clinical variables, and to divide radiologic findings of atlantoaxial ankylosis (AAA) in AS patients into three anatomical components. Methods. The study includes 150 AS patients with either AAA (62 patients) or atlantoaxial subluxation (AAS, 88 patients) who underwent plain radiography of the cervical spine on flexion at our tertiary center for rheumatic diseases. The study subjects’ medical records were reviewed. Lateral plain radiographs of the cervical spine were analyzed by a musculoskeletal radiologist. We compared the results of the modified Stoke Ankylosing Spondylitis Spinal Score (mSASSS) between AAS and AAA patients to determine if mSASSS was related to severity or duration of AS. Results. The mean duration of illness in AS patients with AAA was 19.3 years, and in AAS patients 13.7 years (p＜0.01). The mean total mSASSS of AS patients with AAA was 40.1, and of AAS patients 16.5 (p＜0.001), and was positively associated with the development of AAA and AAS. The odds ratio (OR) of AAA development by cervical spine mSASSS change was higher (OR, 1.079) than the OR (1.049) of lumbar spine mSASSS even after adjusting for age, sex, and disease duration. Conclusion. Although AAA is described infrequently, we found from our data that it is another manifestation of cervical spine involvement in longstanding AS and is related to severity of AS reflected by higher cervical mSASSS.

Keywords: Ankylosing spondylitis, Atlanto-axial joint, Anklyosis