Bulgarian Translation, Cross-Cultural Adaptation, and Validation of the Simple Shoulder Test and the American Shoulder and Elbow Surgeons Shoulder Assessment Form

Background: Patient-reported outcome measures (PROMs) are essential for evaluating functional impairment, treatment effectiveness, and health-related quality of life in patients with musculoskeletal disorders. Among shoulder-specific PROMs, the Simple Shoulder Test (SST) and the American Shoulder and Elbow Surgeons Shoulder Assessment Form (ASES) are widely used instruments with established measurement properties. However, no validated shoulder-specific questionnaire has previously been available in the Bulgarian language. Objective: To translate and culturally adapt the SST and ASES questionnaires into Bulgarian and evaluate their reliability, internal consistency, measurement error, convergent validity, and discriminant validity in patients with shoulder disorders. Methods: Translation and cross-cultural adaptation were conducted following established forward-backward translation guidelines, expert committee review, and pilot testing. A total of 103 patients with shoulder pathology and 42 asymptomatic individuals were included. Construct validity was assessed by examining correlations between the Bulgarian SST (BSST) and Bulgarian ASES (BASES). Test-retest reliability was evaluated using intraclass correlation coefficients (ICC) with a 14-day interval. Internal consistency was determined using Cronbach’s alpha. Discriminant validity, floor and ceiling effects, and measurement error were also analyzed. Results: Strong convergent validity was demonstrated between BSST and BASES (Pearson r = 0.719, p < 0.0001). Test-retest reliability was excellent for both instruments (ICC = 0.96 for BSST and 0.93 for BASES). Internal consistency was acceptable for BSST (Cronbach’s α = 0.77) and good for BASES (Cronbach’s α = 0.86). No significant floor or ceiling effects were observed. Both questionnaires successfully discriminated between patients with shoulder disorders and healthy controls (p < 0.0001). Conclusion: The Bulgarian versions of the SST and ASES demonstrate good reliability and convergent validity and are suitable for assessing shoulder function and pain in Bulgarian-speaking populations. Their availability facilitates clinical evaluation, outcome monitoring, and participation in international research involving shoulder disorders.