Validity and Reliability of the Arabic Version of the Patient-Specific Functional Scale in Individuals with Lateral...

Background/objectives: Lateral elbow pain (LEP) is a common musculoskeletal disorder that can substantially affect upper limb function and daily activities. Patient-reported outcome measures (PROMs) are essential for evaluating functional limitations from the patient's perspective. The Patient-Specific Functional Scale (PSFS) is a patient-centered instrument designed to capture individualized activity limitations. The objective is to evaluate the construct validity, test-retest reliability, and measurement error of the Arabic version of the Patient-Specific Functional Scale (PSFS-Ar) in Arabic-speaking individuals with lateral elbow pain. Methods: A cross-sectional study was conducted in the physiotherapy department at Security Forces Hospital in Riyadh, Saudi Arabia. Sixty-one adults diagnosed with lateral elbow pain completed the PSFS-Ar, the Numeric Pain Rating Scale (NPRS-Ar), and the Upper Extremity Functional Index (UEFI-Ar). Construct validity was examined using Spearman's correlation coefficients and hypothesis testing. Dependent correlations were compared using Steiger's Z test. Test-retest reliability was evaluated in a subgroup of 30 participants using the intraclass correlation coefficient (ICC2,1). Measurement error was quantified using the standard error of measurement (SEM) and minimal detectable change at the 95% confidence level (MDC95). Floor and ceiling effects were also assessed. Results: The PSFS-Ar demonstrated a moderate point estimate of test-retest reliability (ICC = 0.65, 95% CI: 0.35-0.82). The SEM was 1.03 points, and the MDC95 was 2.86 points. Neither of the two prespecified construct-validity hypotheses was confirmed; therefore, construct validity was not supported according to the prespecified hypothesis-testing criterion. The PSFS-Ar showed a weak positive correlation with the UEFI-Ar (r_s = 0.35, p = 0.005) and a negligible, nonsignificant correlation with the NPRS-Ar (r_s = -0.17, p = 0.200). No floor or ceiling effects were observed. Conclusions: The PSFS-Ar demonstrated a moderate but imprecise test-retest reliability estimate, while construct validity was not supported according to the prespecified hypothesis-testing criterion. The wide ICC confidence interval, small reliability sample, systematic change between assessments, variable retest interval, and absence of a validated stability anchor limit confidence in these findings. Further studies using larger samples and standardized retest procedures are required.