Background Atlantoaxial ankylosis (AAA) is another late manifestation of cervical spine involvement in longstanding AS and suggest that higher cervical mSASSS is more related with the development of AAA than atlantoaxial subluxation (AAS). AAA does not cause as much cervical instability as AAS.

Objectives To analyze radiologic and clinical findings of atlantoaxial ankylosis and atlantoaxial subluxation in ankylosing spondylitis

Methods A total of 150 AS patients (145 men, 5 women, mean age, 36.8 years) who had AAA (60 men and 2 women, mean age, 60 years) or AAS (85 men and 3 women, mean age, 34 years) were randomly gathered and underwent at least two plain radiographs of lateral cervical spine on flexion. The atlantodental interval more than 3mm was considered as AAS. Loss of atlantodental interval was considered as AAA. The plain radiographs of lateral cervical spine were independently analyzed by two radiologists. Interobserver reliability between reader 1 and 2 in scoring mSASSS in AS was analyzed. We compared the results of mSASSS between AAS and AAA to see if it was related to severity or duration of the disease.

Results The mean mSASSS of AS patients with AAA and AAS were 40.1 and 16.5 respectively and the mean duration of AS patients with AAA and AAS were 19.3 and 13.7 years each. There was a significantly (p<0.05) higher total mSASSS, especially cervical spine mSASSS, for AS patients with AAA than those with AAS after mSASSS was corrected for age and duration. But, disease duration was not significantly related with the development of AAA compared with that of AAS.

Conclusions We found that it has incidence as high as AAS and both are similar in that they are late presentation of AS and occur in patient with long duration. We found that AAA is another manifestation of cervical spine involvement in longstanding AS and is related to severity of the AS reflected by higher cervical mSASSS.

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Disclosure of Interest None declared