Ultrasound of Subtalar Joint Synovitis in Patients with Rheumatoid Arthritis: Results of an OMERACT Reliability Exercise Using Consensual Definitions

Objective. To evaluate the intraobserver and interobserver reliability of the ultrasonographic (US) assessment of subtalar joint (STJ) synovitis in patients with rheumatoid arthritis (RA). Methods. Following a Delphi process, 12 sonographers conducted an US reliability exercise on 10 RA patients with hindfoot pain. The anteromedial, posteromedial, and posterolateral STJ was assessed using B-mode and power Doppler (PD) techniques according to an agreed US protocol and using a 4-grade semiquantitative grading score for synovitis [synovial hypertrophy (SH) and signal] and a dichotomous score for the presence of joint effusion (JE). Intraobserver and interobserver reliability were computed by Cohen's and Light's kappa. Weighted kappa coefficients with absolute weighting were computed for B-mode and PD signal. Results. Mean weighted Cohen's kappa for SH, PD, and JE were 0.80 (95% CI 0.62-0.98), 0.61 (95% CI 0.48-0.73), and 0.52 (95% CI 0.36-0.67), respectively. Weighted Cohen's kappa for SH, PD, and JE in the anteromedial, posteromedial, and posterolateral STJ were -0.04 to 0.79, 0.42-0.95, and 0.28-0.77; 0.31-1, -0.05 to 0.65, and -0.2 to 0.69; 0.66-1, 0.52-1, and 0.42-0.88, respectively. Weighted Light's kappa for SH was 0.67 (95% CI 0.58-0.74), 0.46 (95% CI 0.35-0.59) for PD, and 0.16 (95% CI 0.08-0.27) for JE. Weighted Light's kappa for SH, PD, and JE were 0.63 (95% CI 0.45-0.82), 0.33 (95% CI 0.19-0.42), and 0.09 (95% CI -0.01 to 0.19), for the anteromedial; 0.49 (95% CI 0.27-0.64), 0.35 (95% CI 0.27-0.4), and 0.04 (95% CI -0.06 to 0.1) for posteromedial; and 0.82 (95% CI 0.75-0.89), 0.66 (95% CI 0.56-0.8), and 0.18 (95% CI 0.04-0.34) for posterolateral STJ, respectively. Conclusion. Using a multisite assessment, US appears to be a reliable tool for assessing synovitis of STJ in RA.