Quantifying the minimal and substantial clinical benefit of the Constant-Murley score and the Disabilities of the Arm, Shoulder and Hand score in patients with calcific tendinitis of the rotator cuff

BACKGROUND: To aid the interpretation of clinical outcome scores, it is important to determine the measurement properties. The aim of this study was to establish the minimal clinically important difference (MCID) and substantial clinical benefit (SCB) for the Constant-Murley score and Disabilities of the Arm, Shoulder and Hand score in patients with long-lasting rotator cuff calcific tendinitis treated with high-energy extracorporeal shockwave therapy and ultrasound guided needling. The secondary purpose was to assess the responsiveness of both questionnaires and to identify variables associated with achieving the MCID and SCB. METHODS: A prospective cohort of 80 patients with rotator cuff calcific tendinitis was analyzed. Two anchor-based methods were used to calculate the MCID and SCB. Effect sizes and standardized response means were calculated to assess the responsiveness. Additional univariate logistic regression analyses were performed to identify factors associated with the achievement of the MCID and SCB. RESULTS: For the Constant-Murley score, we found an MCID and SCB of 9.8 and 19.9, respectively, based on the mean change method and 5.5 and 10.5, respectively, based on receiver operating characteristic analysis. For the Disabilities of the Arm, Shoulder and Hand score, we found an MCID and SCB of –8.2 and –19.6, respectively, with the former and –11.7 and –12.5, respectively, with the latter. The responsiveness of both outcome measures was good, with large effect sizes and standardized response means. The radiographic resorption after 6 weeks and after 6 months appeared to be the most important positive predictor for achieving the MCID and SCB after 6 months. CONCLUSION: This study established the MCID, SCB, and responsiveness for patients with long-lasting rotator cuff calcific tendinitis who were treated with minimally invasive treatment options. With this information, physicians can distinguish between a statistically significant difference and a clinically relevant benefit. Successful radiographic resorption after 6 weeks and after 6 months was associated with achieving clinically significant improvement after treatment.