Validation of the Functional Activity Scoring Tool (FAST): a novel pictorial scale for assessing function in patients with knee osteoarthritis in primary care.

Abstract

Patient-reported outcome measures (PROMs) are crucial for assessing functional ability in patients with knee osteoarthritis. However, existing PROMs have limitations, particularly for individuals with low literacy or non-native English speakers. The Functional Activity Scoring Tool (FAST) was developed as a pictorial-based PROM to address these issues. This study evaluated the validity, reliability and responsiveness of the FAST compared with the Patient-Specific Functional Scale (PSFS) and Knee Injury and Osteoarthritis Outcome Score (KOOS) in patients with knee osteoarthritis. A multicentre prospective cohort study. This study occurred from December 2022 to December 2023 across four public outpatient physiotherapy clinics in Singapore. Data collection was performed on individuals who were clinically diagnosed with knee osteoarthritis. Variables were collected during baseline and follow-up assessments using FAST, PSFS, KOOS and the Global Rating of Change Score. Participants were asked to specify their preferred outcome measure. Validity was assessed via concurrent validity, construct validity through principal component analysis and content validity. The interclass correlation coefficient (ICC) established the test-retest reliability, while responsiveness was evaluated based on changes in PROM scores. 107 participants, aged 66.7±7.7 years, were recruited for data analysis. The FAST showed strong construct and content validity, excellent concurrent validity with the PSFS (Spearman's correlation coefficient (ρ)=0.87-0.90, p<0.001) and moderate to strong validity with the KOOS. The FAST demonstrated moderate test-retest reliability (ICC 0.67, 95% CI 0.37 to 0.81). The correlation between change scores on the FAST and PSFS in the stable, improved and worsened groups was r=0.69, 0.84 and 0.70, respectively. The FAST was preferred by 69% of participants. The FAST is a valid, reliable, responsive and preferred PROM for assessing functional ability in knee osteoarthritis. NCT05590663.