High Reproducibility of an Automated Measurement of Mobility for Patients with Axial Spondyloarthritis

Objective.Conventional measures of spinal mobility used in the assessment of patients with axial spondyloarthritis (axSpA), such as the Bath Ankylosing Spondylitis Metrology Index and its components, are subject to interobserver variability. The University of Córdoba Ankylosing Spondylitis Metrology Index (UCOASMI) is a validated composite index based on a motion video-capture system, UCOTrack. Our objective was to assess its reproducibility in clinical practice settings.Methods.We carried out an observational study of repeated measures in 3 centers. Video-capture systems were installed and adapted to clinical rooms. Patients with axSpA and stable disease were selected by consecutive stratified sampling [disease duration, sex, and the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI)]. Intraobserver reliability of the UCOASMI and of conventional measures was tested 3–5 days apart. For interobserver reliability, 3 patients from each center were evaluated in the other centers, within 3–7 days. The intraclass correlation coefficients (ICC) were calculated.Results.Thirty patients were included (73% men, mean age 53 yrs, mean BASDAI 3.0). Interobserver and intraobserver ICC of the UCOASMI was 0.98. Conventional measurements showed lower but adequate reproducibility as well, except for interobserver reliability of lateral flexion (0.41), cervical rotation (0.61), and Schöber test (0.07), and intraobserver reliability of tragus-to-wall distance (0.30).Conclusion.Reproducibility of the UCOASMI seems very high, and apparently more reliable than conventional measures of mobility.