Development and Validation of a Smartphone-Related Hand Symptoms Questionnaire: A Cross-Sectional and Reliability Study

Background/Objectives: Prolonged smartphone use is associated with musculoskeletal and neurological hand symptoms; however, specialized tools for bilateral assessment remain limited. This study aimed to develop and evaluate the psychometric properties of the Smartphone-Related Hand Symptoms (S-HAND) scale. Methods: A total of 456 participants (mean age: 21.8 ± 6.65 years) were included. The sample was randomly divided into two independent subsamples for Exploratory Factor Analysis (EFA) and Confirmatory Factor Analysis (CFA). Internal consistency was assessed using Cronbach’s alpha and McDonald’s omega coefficients. Test–retest reliability was evaluated in 75 participants using Intraclass Correlation Coefficients (ICC). Measurement precision was determined using the standard error of measurement (SEM) and minimal detectable change (MDC95). Concurrent validity was examined using correlations with general hand pain intensity scores. Results: EFA and CFA supported a three-factor structure consisting of Pain Symptoms, Numbness Symptoms, and Functional Impact. The final CFA model demonstrated excellent fit (CFI = 0.991, TLI = 0.986, RMSEA = 0.049, SRMR = 0.033). Standardized factor loadings ranged from 0.685 to 0.932. Internal consistency was high (Cronbach’s α = 0.857–0.940; McDonald’s ω = 0.863–0.942), and test–retest reliability was excellent (ICC = 0.800–0.907). SEM and MDC95 for the total score were 4.67 and 12.95, respectively. Significant positive correlations with pain intensity scores supported concurrent validity (r = 0.61–0.73, p < 0.001). Conclusions: The S-HAND scale is a reliable and valid instrument for assessing smartphone-related hand symptoms in clinical and research settings.