The experienced sonographers can reach a high intra- and interobserver reliability for the Ultrasound (US) assessment of Subtalar Joint Synovitis in Rheumatoid Arthritis patients, via a consensus-driven US protocol and an agreed scoring system. More extensive studies are required to reveal whether these findings are valid in clinical settings with less-experienced sonographers.

To examine the intraobserver and interobserver reliability of the ultrasonographic (US) assessment of the subtalar joint (STJ) synovitis in rheumatoid arthritis (RA) patients.

An ultrasonographic (US) reliability exercise was performed on 10 RA patients with hindfoot pain after establishing the US protocol by Delphi consensus from 21 sonographers. B-mode and power Doppler (PD) techniques were employed to assess anteromedial, posteromedial and posterolateral STJ. A 4-grade semiquantitative grading score was used for synovitis, and a dichotomous score was used for the presence of joint effusion (JE). Cohen's and Light's κ were used for computation of intraobserver and interobserver reliability. For B-mode and PD signal, computation of weighted k coefficients and absolute weighing was done.

Mean weighted Cohen’s κ 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). Weighted Cohen’s κ 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 κ 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 κ 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.

By employing a multisite assessment, synovitis of STJ in RA can be definitively assessed by US.