Establishing Minimal Clinically Important Difference and Patient Acceptable Symptom State Thresholds for Patient-Reported Outcome Measures in Acromioclavicular Joint Arthropathy: A Prospective Cohort Study.

Introduction: Minimal clinically important difference (MCID) and patient acceptable symptom state (PASS) are essential for interpreting patient-reported outcome measures (PROMs). However, disease-specific thresholds for acromioclavicular (AC) joint arthropathy are not well established, limiting meaningful interpretation of patient-reported outcomes. Materials and Methods: This prospective observational cohort study included adults with symptomatic AC joint arthropathy managed either conservatively or surgically. PROMs - including the Constant-Murley score, American Shoulder and Elbow Surgeons score, University of California Los Angeles score, Quick Disabilities of the Arm, Shoulder and Hand, Western Ontario Rotator Cuff (WORC) index, and visual analogue scale for pain - were collected at baseline and 12 months. MCID, substantial clinical benefit (SCB), and maximum outcome improvement (MOI) were determined using anchor-based methods with a global rating of change scale and receiver operating characteristic analysis, supported by distribution-based estimates. PASS thresholds were derived using a patient satisfaction anchor. Thresholds were calculated separately within surgical and conservative treatment contexts in accordance with Consensus-based Standards for the Selection of Health Measurement Instruments recommendations. Results: A total of 170 patients (100 conservative, 70 surgical) completed a 12-month follow-up. All PROMs demonstrated excellent reliability (intraclass correlation coefficient range, 0.85-0.96) and strong anchor validity (Spearman r, 0.51-0.62; P < 0.001). Anchor-based MCID values differed across PROMs and treatment contexts but consistently exceeded measurement error. The WORC index demonstrated the highest responsiveness (area under the curve, 0.84; standardised response mean, 0.85). PASS thresholds reflected acceptable symptom states across PROMs, and approximately 92% of patients achieving MCID also met PASS criteria. Thresholds were derived independently within each treatment context and were not intended for comparative assessment of treatment effectiveness. Conclusion: This study establishes disease-specific MCID, SCB, MOI, and PASS thresholds for commonly used shoulder PROMs in AC joint arthropathy. These benchmarks enhance the interpretability of patient-reported outcomes, support standardised reporting in clinical research, and should be applied as measurement tools rather than indicators of comparative treatment efficacy.