Background: The Western Ontario rotator cuff index (WORC) is an increasingly applied condition-specific outcome measure for rotator cuff (RC) conditions. However, in most WORC validation studies, only a limited number of psychometric properties are studied in indistinct patient groups.
Purpose: To assess psychometric properties of the WORC according to the Scientific Advisory Committee quality criteria for health questionnaires in 3 patient groups with distinct RC conditions.
Study design: Cohort study (diagnosis); Level of evidence, 2.
Methods: The WORC (range, 0-100; 21 items, 5 domains) was administered twice (T1, T2) in 92 patients (35 RC tears, 35 calcific tendinitis, 22 impingement). Additionally, the Constant score (CS) and the Disabilities of the Arm, Shoulder and Hand score (DASH) were recorded. Calcific tendinitis patients were reassessed 6 weeks after treatment with needling and lavage or a subacromial injection with corticosteroids (T3). We assessed floor and ceiling effects, internal consistency, test-retest reliability, precision, construct validity, minimally detectable change, and responsiveness in the diagnostic subgroups and the total group.
Results: Mean age was 55.0 ± 8.7 years, and 49 of 92 (53%) patients were female. Mean baseline WORC was 46.8 ± 20.4, CS was 63.9 ± 15.4, and DASH was 40.9 ± 18.6. Significant differences were found for the CS and DASH between RC tear patients (severe symptoms) and the other patients, but not for the WORC. There were no floor and ceiling effects. Internal consistency was high: the Cronbach alpha coefficient was .95. The intraclass correlation coefficient of .89 and standard error of measurement of 6.9 indicated high reproducibility. Pearson correlations of the WORC with the CS and DASH were .56 and -.65, respectively (both P < .001). At T3, total WORC improved significantly (mean change, 18.8; 95% confidence interval, 11.3-26.2). Correlations of the WORC change scores with CS and DASH changes were .61 and -.84, respectively (both P < .001). Effect size was 0.96, with a standardized response mean of 0.91, indicating good responsiveness.
Conclusion: Applied to a variety of RC patients, the WORC had high internal consistency, moderate to good construct validity, high test-retest reliability, and good responsiveness. These findings support the use of the WORC as a condition-specific self-reported outcome measure in RC patients, but its validity in patients with severe symptoms needs further investigation.