Development and psychometric testing of a novel scale for shoulder assessment

Current patient-reported outcome measures (PROMs) are long, have complex scoring systems, suffer from ceiling and floor effects, are not universally applicable, and have a high administrative burden. In response, we have developed the Subjective Shoulder Scale (S3), a novel PROM designed to overcome these limitations and provide a comprehensive, efficient, and patient-centered evaluation of 7 key domains.

Items for S3 were generated by reviewing existing questionnaires and refined using input from patients and an expert panel. Seven questions assess pain, range of motion, strength, shoulder stability, activities of daily living, sports and leisure activities, and mental well-being. After pilot testing in 20 participants, test-retest reliability was evaluated in 100 participants by calculating Cronbach's alpha and the intraclass correlation coefficient. To test validity and responsiveness, 124 participants completed both the S3 and the American Shoulder and Elbow Surgeons questionnaire before and after undergoing various shoulder procedures. Pearson's correlation coefficients, exploratory factor analysis, and responsiveness were determined by calculating the effect size and establishing thresholds for the minimal clinically important difference, substantial clinical benefit, and patient-acceptable symptom state.

Pilot testing confirmed clarity, relevance, readability, and ease of use. In the full psychometric evaluation cohort of 244 participants (mean ± standard deviation age 59 ± 13 years; 50% females), the S3 exhibited excellent test-retest reliability (intraclass correlation coefficient = 0.96) and high internal consistency (Cronbach's α = 0.93). No ceiling or floor effects were observed. Exploratory factor analysis supported a unidimensional structure, and convergent validity was established through a strong positive correlation with the American Shoulder and Elbow Surgeons questionnaire (r = 0.71, P < .001). S3 is also responsive, with thresholds of 12.4 points for minimal clinically important difference, 19.9 points for substantial clinical benefit, and 38-83 points for patient acceptable symptom state.

S3 is a reliable, valid, responsive PROM for capturing the effects of diverse shoulder conditions. By addressing weaknesses of existing questionnaires, S3 may facilitate personalized treatment planning through more efficient, meaningful patient evaluations.