To select the most appropriate radiologic scoring method for the evaluation of radiographic progression in ankylosing spondylitis (AS) in clinical trials.

The validity of the currently available methods, the Bath Ankylosing Spondylitis Radiology Index (BASRI), the Stoke Ankylosing Spondylitis Spine Score (SASSS), and the modified SASSS (M‐SASSS), was tested according to the aspects of the Outcome Measures in Rheumatology Clinical Trials filter: truth, discrimination (reliability and sensitivity to change), and feasibility, using radiographs of 133 patients at 4 different time points (baseline, 1 year, 2 years, and 4 years). One observer scored these sets in chronological order. To assess interobserver reliability, a second observer scored radiographs of 20 patients at the 4 different time points.

After 4 years, 9% and 8% of patients showed changes >0 in the sacroiliac (SI) joints and hips, respectively. Independent of the method chosen, ∼40% of patients showed changes in both the lumbar and cervical spine. Therefore, it was concluded that, for the assessment of progression, SI joints and hips are of minor importance. The intraclass correlation coefficient (ICC) varied from 0.87 to 0.98 and ICCs for intraobserver scores varied from 0.96 to 0.99. Concerning progression scores, only the ICC for the M‐SASSS measured after 2 years remained acceptable (0.82). The intraobserver scores for progression after 2 years of followup were an ICC of 0.93 for the BASRI, an ICC of 0.79 for the SASSS, and an ICC of 0.95 for the M‐SASSS. Concerning sensitivity to change, it was found that the M‐SASSS classified the highest percentage of patients with a change >0.

The M‐SASSS is the most appropriate method by which to score the radiographic progression in AS patients in clinical trials.