LAUSR

In rheumatoid arthritis (RA), foot synovitis is frequently evident in patients in DAS-28 remission, placing them at risk of radiographic joint damage. This has been attributed to the omission of foot and ankle joint counts from the DAS-28. The Rheumatoid Arthritis Foot Disease Activity Index (RADAI-F5) is a valid, reliable, and feasible tool and can be used as an adjunct to the DAS-28 to quantify foot disease activity. Recent qualitative research suggests that rheumatologists perceive validation of the RADAI-F5 against musculoskeletal ultrasonography (MSUS) as essential prior to clinical implementation. Accordingly, this study aimed to evaluate the construct validity of the RADAI-F5 relative to MSUS and clinical examinations of foot disease activity. People with RA were recruited from 3 NHS Rheumatology Outpatient services in Scotland. Participants attended a single research visit and completed the RADAI-F5. An MSUS-trained podiatrist performed multi-planar grayscale (GS) and power Doppler (PD) MSUS assessments on 17 regions of each foot, including joints and soft tissues and evaluated foot disease activity using summated scores based on semi-quantitative grading systems for synovial hypertrophy, PD synovitis, tenosynovitis (0-39) and presence/absence of erosions (0-7). An independent examiner clinically assessed the same 17 regions for swelling and tenderness and scored using a summated score for presence/absence (0-17). The construct validity of the RADAI-F5 was assessed using Spearman’s correlation coefficients with 95% confident intervals (95% CI) to test a priori-specified hypotheses for strength of associations. Of 60 participants, 48 were female, with a mean [standard deviation, ± SD] age of 62.6 ± 9.96 and median RA disease duration of 10 (interquartile range 6-20.5) years. For DAS28-ESR disease categories, 10% were in remission, 35% had low disease activity, 18.3% had moderate disease activity, and 36.7% had high disease activity. Forty-three participants were receiving DMARD therapy, and 17 were receiving biologics. Theoretically consistent associations confirming construct validity [95% CI] were observed between the RADAI-F5 and MSUS GS-detected synovial hypertrophy (0.72 [0.57-0.82]; strong) and MSUS PD-detected synovitis (0.50 [0.28-0.67]; moderate), MSUS-detected erosions (0.42 [0.19-0.61]; moderate) and clinical tenderness (0.52 [0.31-0.68]; moderate), and swelling (0.35 [0.11-0.55]; weak). Moderate-strong associations between RADAI-F5 and MSUS provide additional evidence of the excellent measurement properties of this tool. The RADAI-F5 scores, as anticipated, were more strongly associated with MSUS-detected synovial hypertrophy compared to clinical examinations of swelling and tenderness. With increased confidence in the RADAI-F5's validity, clinical implementation of the RADAI-F5 could help with the early identification of people with RA who are at risk of poor functional and radiographic outcomes. The RADAI-F5 has the potential for use in a broad range of clinical applications within podiatry and rheumatology, including triage, enhanced multidisciplinary team and patient-clinician communication, and remote consultations. Disclosure A. Hoque: None. M. Steultjens: None. D. Dickson: None. G.J. Hendry: None.