BACKGROUND:Acromioclavicular (AC) joint (ACJ) pathology is a common cause of shoulder dysfunction, and treatment recommendations vary. When the efficacy of treatment is evaluated, the ability to measure outcomes specific to the population is essential. The aim of the current research was to develop and validate a specific ACJ questionnaire. METHODS:Items for the "Specific AC Score" (SACS) were generated through the use of an expert panel, existing questionnaires, and patient feedback. Preliminary data analysis identified redundancy of items resulting in the questionnaire being refined. The final SACS was evaluated in 125 patients requiring surgical intervention of the ACJ. Internal consistency (the Cronbach α and corrected item-total correlation), content validity, criterion validity, responsiveness, and test-retest reliability (intraclass correlation coefficient) were examined and compared with the Shoulder Pain and Disability Index, Oxford Shoulder Score, and American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form. The minimum detectable change score was calculated. RESULTS:The Cronbach α for the total scale preoperatively and postoperatively was high (preoperatively = 0.91, postoperatively = 0.93). All 3 domains (Pain, Function, Quality of Life) demonstrated acceptable internal consistency (α > 0.70), and the correlation between items in each domain was satisfactory. The responsiveness was excellent (effect size, -2.32; standard response mean, -1.85) and was higher than the other general shoulder questionnaires. There were no relevant floor or ceiling effects. Reliability was high (intraclass correlation coefficient, 0.89) and the minimum detectable change was 6.5 points. DISCUSSION:This new ACJ-specific questionnaire has been robustly developed, has good measurement properties, and has excellent responsiveness. The SACS is recommended for measuring outcomes in ACJ patients.