Development and Validation of a Short-Form Version of the Western Ontario Shoulder Instability Scale (Short-WOSI)

Abstract

Background: Patient-reported outcome measures (PROMs) have transitioned from primarily being used as research instruments to becoming increasingly used in the clinical setting to assess recovery and inform shared decision-making. However, there is a need to develop validated short-form PROM instruments to decrease patient burden and ease incorporation into clinical practice. Purpose: To assess the validity and responsiveness of a shortened version of the Western Ontario Shoulder Instability Index (Short-WOSI) when compared with the full WOSI and other shoulder-related PROM instruments. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: This study was a secondary analysis of data collected as part of an institutional review board–approved, multicenter cohort of 1160 patients undergoing surgical stabilization for shoulder instability. The following PROMs were captured preoperatively and 2 years after surgery: WOSI, American Shoulder and Elbow Surgeons (ASES) score, the Single Assessment Numeric Evaluation (SANE), and 36-Item Health Survey (RAND-36). The cohort was split into 2 data sets: a training set to be used in the development of the Short-WOSI (n = 580) and a test set to be used to assess the validity and responsiveness of the Short-WOSI relative to the full WOSI, ASES, SANE, and RAND-36. Results: The Short-WOSI demonstrated excellent internal consistency before surgery (Cronbach α = .83) and excellent internal consistency at the 2-year follow-up (Cronbach α = .93). The baseline, 2-year, and pre- to postoperative changes in Short-WOSI and WOSI were closely correlated ( r > 0.90), with both demonstrating large effect sizes (Short-WOSI = 1.92, WOSI = 1.81). Neither the Short-WOSI nor the WOSI correlated well with the other PROM instruments before ( r = 0.21-0.33) or after ( r = 0.25-0.38) surgery. The Short-WOSI, WOSI, and SANE scores were more responsive than ASES and RAND-36 scores. Conclusion: The 7-item Short-WOSI demonstrated excellent internal consistency and a lack of floor or ceiling effects. The Short-WOSI demonstrated excellent cross-sectional and longitudinal construct validity and was similarly responsive over time as the full WOSI. Neither the Short-WOSI nor WOSI correlated with more general shoulder PROMs, underscoring the advantage of using instability-specific instruments for this population.