Reproducibility: Reliability and agreement of short version of Western Ontario Rotator Cuff Index (Short-WORC) in patients with rotator cuff disorders

INTRODUCTION: Recently, a shorter version of Western Ontario Rotator Cuff Index (Short-WORC) was proposed as a subset of 7 items from the original 21-item WORC. However, the reproducibility of the Short-WORC has not been established. PURPOSE OF THE STUDY: To determine reproducibility (reliability and agreement) of the Short-WORC among patients with rotator cuff disorders (RCDs). METHODS: Patients (n = 153) diagnosed with RCD completed the WORC at baseline and at 3 months post-operatively (n = 146). The Short-WORC was extracted from the full version of WORC. From this retrospective cohort, 43 patients were retested within 5 weeks, if they remained stable. Cronbach's alpha (α) and intra class correlation coefficients (ICC2,1) were used to assess internal consistency and test-retest reliability respectively. Standard error measurement (SEM), minimal detectable change (MDC90) and Bland Altman (BA) plots were used to assess agreement. RESULTS: No floor and ceiling effects were reported for either the Short-WORC or WORC. Cronbach's α were 0.84 and 0.90 at baseline and 0.89 and 0.95 at 3 month of follow up for Short-WORC and WORC respectively. The ICC2,1 were 0.89 and 0.91 for the Short-WORC and WORC respectively. The agreement parameters for the Short-WORC were: SEMagreement = 8.8, MDC90individual = 20.3, MDC90group = 5.1. We found substantial agreement between the two versions of WORC on BA plots with minimal (mean difference (d) <1) systematic differences between them. The limits of agreement (LOA) between two versions of WORC were similar across sessions and fell within range of -11.7 to 13.2 points at test and -14.7 to 14.7 points at retest. CONCLUSION: Short-WORC and WORC demonstrates strong reproducibility and can be used for group and individual comparison of health-related quality of life (HRQoL) among patients with RCD. Wider LOA may be expected when using the Short-WORC for individual patient assessment. Reproducibility data is essential, but should be supplemented by validation of actual Short-WORC with samples representing the spectrum of RCD. LEVEL OF EVIDENCE: N/A.