The Responsiveness and Minimal Important Change (MIC) of the Western Ontario Shoulder Instability Index (WOSI) and Oxford Shoulder Instability Score (OSIS).

Abstract

Study Design A prospective cohort study. Background Patient Reported Outcome Measurements (PROMs) are widely used to evaluate functional limitations. Considering PROMs for shoulder instability, information is lacking with regard to what constitutes a relevant change from baseline scores. Objectives To evaluate the responsiveness of the Western Ontario Shoulder Instability Index (WOSI) and the Oxford Shoulder Instability Score (OSIS) and estimate their Minimal Important Change (MIC). Methods 105 consecutive patients with shoulder instability completed five PROMs at baseline and at 6-months follow-up. The PROMs included the WOSI and OSIS, the Simple Shoulder Test (SST), the Oxford Shoulder Score (OSS) and the Disability of the Arm, Shoulder, and Hand assessment (DASH). Patients also rated their functional change on an anchor question at follow-up. Responsiveness was evaluated by testing nine hypotheses regarding pre-defined correlations between the changes in PROM scores, by calculating the area under the Receiver Operating Characteristic (ROC) curve, and by calculating the Standard Response Mean (SRM) and Effect Size (ES) statistics. The MIC was determined by identifying the optimal cut-off on the ROC curve. Results Seven out of nine hypotheses (78%) were confirmed; as expected a high correlation (0.77) was found between change scores of the WOSI and OSIS, whereas the correlations of the changes in WOSI and OSIS with changes in general shoulder PROMs were slightly lower (0.61-0.75). The area under the curve (AUC) was 0.83 (95% CI 0.75-0.91) for the OSIS and 0.82 (95% CI 0.74-0.90) for the WOSI. The MIC was about 6 points for the OSIS and about 14 points for the WOSI. Conclusion Both the WOSI and OSIS are able to measure change in shoulder function in patients with shoulder instability. The estimated MIC is 6 points for the OSIS (on a scale from 0-48) and 14 points for the WOSI (on a scale from 0-100). J Orthop Sports Phys Ther, Epub 12 May 2017. doi:10.2519/jospt.2017.6548.