Mishal M Aldaihan, Abdulrahman M Alsubiheen, Ali H Alnahdi
Background/Objective: The Patient-Specific Functional Scale (PSFS) is a patient-centered outcome measure that captures limitations in activities that are personally meaningful to patients. Although the Arabic PSFS has demonstrated acceptable validity and reliability, its responsiveness in individuals with lower extremity musculoskeletal disorders has not been established. This study aimed to examine the responsiveness of the Arabic PSFS in detecting changes in lower extremity function over time. Methods: A prospective cohort study was conducted in three outpatient physical therapy clinics in Riyadh, Saudi Arabia. Seventy-two adults with lower extremity musculoskeletal disorders receiving physical therapy care completed the Arabic PSFS, RAND-36, and Numeric Pain Rating Scale (NPRS) at baseline and follow-up. At the follow-up, participants also completed the Global Rating of Change (GRC). Responsiveness was evaluated using eight a priori hypotheses following COSMIN recommendations. Change scores were analyzed using correlation coefficients, paired t-tests, effect size (ES), and standardized response mean (SRM). Results: Sixty participants (83.3%) reported improvement in the GRC. PSFS scores improved significantly (mean difference = 1.66; p < 0.001), demonstrating a large magnitude of improvement (ES = 0.80; SRM = 0.92). PSFS change scores correlated moderately with RAND-36 physical functioning (r = 0.51) and GRC (r = 0.55) and weakly with emotional well-being (r = 0.26) and showed smaller-than-expected associations with pain measures. Six out of eight (75%) predefined hypotheses were confirmed. Conclusions: The Arabic PSFS demonstrates sufficient responsiveness in detecting improvement in lower extremity function and is suitable for monitoring rehabilitation outcomes in Arabic-speaking adults with lower extremity musculoskeletal disorders receiving outpatient physical therapy.