Costotransverse joint ankylosis and their association with syndesmophyte progression in patients with radiographic axial spondyloarthritis

Background:Abnormal new bone formation can occur not only in the vertebral body but also can occur in facet, costovertebral, and costotransverse joints in radiographic axial spondyloarthritis (r-axSpA) patients. Little is known about the association between syndesmophyte progression and paravertebral joint ankylosis in r-axSpA.Objectives:Costotransverse joint ankylosis in r-axSpA patients was measured. Furthermore, the association between syndesmophyte progression for 2 years assessed by computed tomography syndesmophyte score (CTSS) and facet, costovertebral, and costotransverse joints ankylosis were evaluated.Design:Single-center, prospective, cohort study.Methods:Whole spine CT images taken at baseline and 2-year follow-up were used to calculate the CTSS of the vertebral body. In addition, ankylosis of the facet/costovertebral/costotransverse joints was scored. CTSS (range, 0–552) and facet joint ankylosis (range, 0–46) were assessed at 23 vertebral units. Costovertebral joints at T1–T12 (range, 0–48) and costotransverse joints at T1–T10 (range, 0–20) were also assessed by independent two readers. Intraclass correlation coefficients (ICC) were calculated to determine inter-reader reliability. Odds ratios (OR) were calculated to identify the associations between syndesmophyte progression and the baseline status of facet, costovertebral, and costotransverse joints.Results:In all, 50 patients with r-axSpA were included. Readers 1 and 2 identified C7–T3 (facet joints), T5–T7 and T12 (costovertebral joints), and T8–T9 (costotransverse joints), as common sites of ankylosis at baseline and at 2-year follow-up. The ICCs for the facet, costovertebral, and costotransverse joints at baseline were 0.876, 0.952, and 0.753, respectively. OR of baseline costovertebral and costotransverse joint ankylosis for predicting syndesmophyte progression of the vertebral body was 4.644 [95% confidence interval (CI), 2.295–9.398] and 1.524 (95% CI, 1.036–2.244), respectively.Conclusion:Costotransverse joint ankylosis in r-axSpA patients can be measured semi-quantitatively on whole spine CT, and ankylosis of the costotransverse and costovertebral joints predicts the progression of syndesmophytes. Trial registration: Not applicable.