Prevalence and associated factors of facet joint ankylosis in patients with axial spondyloarthritis

To investigate the prevalence of facet joint ankylosis in the whole spine in axial spondyloarthritis (axSpA) using low dose computed tomography (ldCT), and to identify factors associated with facet joint ankylosis.Whole spine ldCT images from 161 patients with axSpA were examined, and the presence of facet joint ankylosis was assessed (right and left, C2-S1) by two readers. Facet joint ankylosis was scored from 0-46. Structural damage of vertebral body was assessed using CT syndesmophyte score (CTSS). Factors associated with ankylosed facet joint scores for the whole spine were identified using a generalized linear model with a negative binomial distribution.Seventy-nine patients (49%) and seventy patients (40%) (reader 1 and reader 2, respectively) had one or more ankylosed facet joint. Facet joint ankylosis was most common in the thoracic spine. The mean score of facet joint ankylosis for the whole spine was 6.6 ± 11.2 in reader 1 and 4.2 ± 8.4 in reader 2. Whole spine facet joint ankylosis score positively correlated with ASDAS and CTSS. In multivariable analysis, the ankylosed facet joint score was associated with ASDAS, sacroiliitis, CTSS, and a history of uveitis in both readers. Uveitis history, ASDAS and CTSS were associated with whole spine facet joint ankylosis score in subgroup analysis of only radiographic-axSpA.The prevalence of ankylosed facet joints is high in axSpA, especially in the thoracic segment. The whole spine ankylosed facet joint score is significantly associated with a history of uveitis, ASDAS, sacroiliitis, and syndesmophyte score.