Translation, cultural adaptation and psychometric validation of the Shoulder Pain and Disability Index into Finnish

Shoulder pain is a leading cause of disability, often resulting in functional limitations and reduced quality of life. Valid, culturally adapted patient-reported outcome measures (PROMs) are essential for assessing symptoms and treatment outcomes across populations. The Shoulder Pain and Disability Index (SPADI) is widely used internationally, but no validated Finnish version has been available. This study aimed to translate, culturally adapt, and psychometrically validate a Finnish version of the SPADI for use in Finnish-speaking patients with shoulder pain. Translation followed International Society for Pharmacoeconomics and Outcomes Research (ISPOR) guidelines, including forward and back translation, expert review, and cognitive debriefing with 10 patients. Psychometric validation was conducted in 179 patients at Helsinki University Hospital; 137 also completed retest assessments after 12–21 days. We evaluated internal consistency, test–retest reliability, factor structure, floor and ceiling effects, and convergent validity using Cronbach’s alpha, intraclass correlation coefficients (ICC), exploratory factor analysis, and predefined hypothesis testing based on Pearson correlations with other PROMs: QuickDASH, Oxford Shoulder Score (OSS), Constant-Murley Score, American Shoulder and Elbow Surgeons score (ASES), and Simple Shoulder Test (SST). The Finnish SPADI demonstrated excellent internal consistency (α = 0.96) and test–retest reliability (ICC = 0.91). Pain (α = 0.93; ICC = 0.89) and disability (α = 0.94; ICC = 0.89) subscales were similarly robust. No floor or ceiling effects were observed for total scores, although several disability items showed ceiling effects. Convergent validity was strong, with high correlations between SPADI and QuickDASH (r = 0.85), OSS (r = 0.88), Constant-Murley (r = 0.83), ASES (r = 0.80), and SST (r = 0.81) scores, confirming all predefined hypotheses. Factor analysis supported a two-dimensional structure separating pain and disability. The Finnish SPADI exhibits strong linguistic validity and excellent psychometric properties, providing a reliable tool for assessing shoulder pain and disability in Finnish-speaking populations. Study registration: 26 October 2022 at Clinical trials (NCT05598541).