Development, Validation, and Interpretation of the Rheumatoid Arthritis Foot Disease Activity Index (RADAI-F5)
Authors:   , Hoque Anika 
Published: August 2024

Introduction: Rheumatoid arthritis (RA) frequently manifests in the foot and ankle, resulting in a decline in functional ability and overall quality of life. Early detection and intervention of foot inflammation is vital for optimising RA management and enhancing patient outcomes. However, the lack of a valid and reliable measure to assess foot disease in RA, coupled with the omission of these joints from disease indices and infrequent foot examinations in rheumatology settings, poses significant challenges and frequently results in suboptimal management of foot symptoms. To address this, the Rheumatoid Arthritis Foot Disease Activity Index (RADAI-F5) has emerged as a valid and reliable patient-reported outcome measure (PROM) that evaluates RA foot disease activity. A comprehensive examination of the clinical barriers and facilitators related to the tools implementation is essential to ensure its successful integration into rheumatology care settings. Musculoskeletal ultrasound (MSUS) has gained recognition as a valuable imaging technique for RA within rheumatology and podiatry settings. As indicated by rheumatologists, further validation is required to validate the RADAI-F5 against objective measures including clinical examination and MSUS. Moreover, additional evaluation of the measurement properties of the RADAI-F5, which includes determining the minimally important difference (MID) and assessing the tool's predictive validity, is imperative to allow for adequate clinical application and interpretation of the tool. Therefore, the primary objective of this thesis is to further validate and interpret the RADAI-F5, with the goal of effectively integrating it into routine clinical practice. Methods: This research employed a multi-method approach consisting of five studies; integrating qualitative and quantitative methods. Study 1 employed qualitative methodology to explore the perspectives of RA patients and clinicians on the clinical utility of the RADAI-F5. Themes were identified through interpretative phenomenological analysis. Study 2 employed a cross-sectional design, where the construct validity of the RADAI-F5 was evaluated compared to MSUS and clinical examination. The validity was assessed through correlation coefficients and a priori-specified hypotheses. Study 3 was a longitudinal study to determine the MID of the RADAI-F5 in participants initiating biologic medication. These participants completed the RADAI-F5 assessments at baseline and three months and the MID was calculated using an anchor-based method. Study 4 investigated the efficacy of the RADAI-F5 in capturing disease activity in the tibiotalar joints (TTJ) and subtalar joints (STJ), utilising data from Study 2. Multivariable linear regression analyses explored the relationship between the RADAI-F5 scores and these structures. Lastly, Study 5 examined the predictive validity of the RADAI-F5 for adverse self-reported foot disability and impairment outcomes at 12 months, using previously published data. Binary logistic regression analysis was employed to assess the predictive validity of the RADAI-F5. Results: Study 1 highlighted the potential value of the RADAI-F5 as a clinical tool to promote communication, guide management, help screen foot symptoms, monitor foot disease status, and promote patient education. Nevertheless, one of the main barriers highlighted by key stakeholders included the necessity for further validation of the tool against objective measures. In Study 2, the construct validity of the RADAI-F5 was established by demonstrating moderate-to-strong correlations between the instrument and MSUS-detected foot disease. Study 3 established the MID for the RADAI-F5, yielding a value of 1.02. This knowledge provides initial insights into RADAI-F5 score changes, which holds promise to assist in guiding management decisions in line with patients’ perspectives of meaningful change. Results from Study 4 indicate a significant association between active foot arthritis at the TTJ or STJ and higher RADAI-F5 scores. This finding confirms the tools capability to capture disease in these structures, from a data-driven approach. Lastly, Study 5 revealed that two consecutive episodes of moderate-to-high foot disease activity serves as a significant predictor of foot disability in early RA patients. These preliminary findings support the predictive validity of this novel tool. Conclusion: The RADAI-F5 demonstrates good measurement properties and offers an opportunity to enhance RA foot disease detection and treatment within the therapeutic ‘window of opportunity’. The clinical application of this instrument shows potential in enhancing patients’ foot outcomes and consequently, quality of life. Collectively, these findings further contribute to the validation and reliability of the tool, while also considering the perspectives of key stakeholders for successful implementation of the RADAI-F5 into rheumatology care settings. Overall, this tool holds potential for early foot disease detection in RA patients, enabling timely interventions to improve radiographic outcomes and functional disability.