Objective: To investigate the degree of ossification and the frequency of ankylosis between the atlas and the dens of the axis in patients with longstanding ankylosing spondylitis (AS), to assess radiological involvement of the cervical spine, and to determine their correlations with structural severity and clinical variables, including neurological abnormalities.
Methods: In 61 AS patients with disease duration over 7 years, the findings of conventional radiographs were graded by the Bath Ankylosing Spondylitis Radiology Index (BASRI), and the ossification levels between the atlas and the dens and the severity of zygapophyseal (ZA) joint lesions were scored using multislice CT. Neurological examinations and somatosensory evoked potentials (SSEP) were performed by neurologists.
Results: According to the BASRI, 50 patients (82.0%) had radiological changes of the cervical spine > or = score 1. Thirty-seven patients (60.6%) revealed a certain extent of the atlantodental ossification, and the presence of partial or complete atlantodental ankylosis was seen over 30% of the patients. The BASRI-cervical spine score and the atlantodental ossification levels correlated with disease duration. ZA involvement was observed in 49 patients (80.3%), including 23 with ZA fusion (37.7%). Although 4 of 11 patients with atlantoaxial subluxation showed abnormal SSEP none had significant neurological complications. This might be attributed in part to atlantodental ankylosis and ZA fusion. Finally, ossifications of the anterior and posterior longitudinal ligaments were found 26.2 and 29.5%, respectively.
Conclusion: Cervical spine involvement and atlantodental ossification or ankylosis appear to be common in patients with longstanding AS, and to be particularly more severe in patients with a longer disease duration.