Minimal clinically important differences in Rowe and Western Ontario Shoulder Instability Index scores after arthroscopic repair of anterior shoulder instability

Background: The minimal clinically important difference (MCID) is the threshold value for a change that would be considered meaningful by the patient. The purpose of this study was to determine the MCIDs for the Rowe score and the Western Ontario Shoulder Instability Index (WOSI) score after arthroscopic repair of anterior shoulder instability. Methods: The study enrolled 198 patients who underwent an arthroscopic stabilization procedure for anterior shoulder instability. Patients were assigned to no change and minimal change groups by a 15-item questionnaire at the 1-year postoperative visit. The Rowe and WOSI scores were assessed preoperatively and at a 1-year postoperative follow-up. The MCID was calculated using an anchor-based method and a distribution-based method. Results: There were 9 patients in the no change group and 26 patients in the minimal change group. The MCID for the Rowe score was 9.7 according to the anchor-based method. By the anchor-based method, the authors could not calculate MCID for the WOSI score because of insignificant difference of the mean score changes between the no change and minimal change groups. By the distribution-based method, MCIDs for the Rowe and the WOSI scores were 5.6 and 151.9 with the standard deviation–based estimate and 2.2 and 60.7 with the effect size–based estimate, respectively. Conclusions: To assess the effectiveness of an arthroscopic stabilization procedure for anterior shoulder instability using the Rowe score, a difference of at least 9.7 in the score is clinically relevant. To compare clinical outcomes between different modalities, we should consider not only statistically significant differences but also the MCID.