The Western Ontario Shoulder Instability Index (WOSI): validity, reliability, and responsiveness retested with a Swedish translation

Background and purpose The WOSI score questionnaire is a tool designed for self-assessment of shoulder function for patients with instability problems. We made a translation into Swedish and retested the score by analyzing the psychometric properties validity, reliability, and responsiveness. Patients and methods 3 patient materials were used for the assessment: (A) a follow-up on a group of 32 patients more than 8 years after having primary posttraumatic shoulder dislocation. Evaluation of Pearson’s correlation coefficient between WOSI and Rowe score and for test-retest reliability was made; (B) 22 patients, treated with a surgical stabilization of the shoulder at our department, were evaluated with Pearson’s correlation coefficient between WOSI and EQ-5D, and between WOSI and a VAS-scale of general shoulder function. Also, Cronbach’s alpha, effect size, and floor, and ceiling effects were analyzed; (C) 45 students with healthy shoulders (reference group) had their WOSI score determined. Results The construct validity (Pearson’s correlation coefficient) was adequate (0.59) between the WOSI score and the Rowe score. The agreement with an ICC value (test-retest) for the WOSI score was excellent (0.94). Cronbach’s alpha (internal consistency) was satisfactory, with 0.89 preoperatively and 0.95 postoperatively. All 22 patients in group B reported improvement in the WOSI score (mean 29%). Responsiveness was excellent, with an effect size of 1.67 for the WOSI score. There were no floor or ceiling effects for the Swedish WOSI score. The mean WOSI score from group C with 45 normal healthy shoulders was 96%, with no floor but high ceiling effects. Interpretation WOSI score does not require an examination of the patient and can be administered by mail. The high ICC and sensitivity makes it able to monitor an individual patient’s progress. At this retest, the WOSI score has good validity, a high degree of reliability, and a high degree of responsiveness, all at the same level as in the original publication. We recommend the WOSI when evaluating patients with instability problems.