Reliability, validity and responsiveness of the Chinese version of the Rotator Cuff Quality of Life Index (RC-QOL) in patients with rotator cuff disorders

Background: The Rotator Cuff Quality of Life Index (RC-QOL) is a scale designed to evaluate the impact of rotator cuff (RC) disorders on the general quality of life of patients. Our study aims to adapt the RC-QOL into Chinese and to assess its reliability, validity and responsiveness in Chinese patients with RC disorders. Methods: First, we developed the Chinese version of RC-QOL (C-RC-QOL) through a five-step procedure. Next, the recruited patients gave three rounds of responses to the C-RC-QOL, Medical Outcomes Study Short Form 36 (SF-36) and Oxford Shoulder Score scales (OSS). Then, we calculated the Cronbach’s alpha, standard error of measurement (SEM), minimally detectable change (MDC), intra-class correlation coefficient (ICC), Pearson's correlation coefficient (r), effect size (ES) and standardized response mean (SRM) to evaluate the reliability, validity and responsiveness of the C-RC-QOL respectively. The unidimensionality of each subscale was assessed by principal component analysis (PCA) of the residuals. Results: Overall, 124 patients with RC disorders successfully completed the first two rounds of the scales, and 108 patients completed the last round of the scales. Good or excellent internal consistency (Cronbach’s alpha = 0.953) was found in the overall scale and subscales of the C-RC-QOL, and good or excellent test-retest reliability (ICC = 0.854) was found as well. The SEM and MDC values of the C-RC-QOL were 4.6 and 12.8 respectively. Moderate, good or excellent correlations (r = 0.452–0.839) were obtained between the physical subscales of the C-RC-QOL and the OSS, as well as the physical subscales of the SF-36; similar results were obtained between the emotion subscale of the C-RC-QOL and the mental subscales of the SF-36 (r = 0.490–0.733), which, illustrated the good validity of the C-RC-QOL. In addition, high responsiveness was observed in the overall scale and subscales of the C-RC-QOL (ES = 1.77, SRM = 1.98). The unidimensionality of five subscales was respected according to PCA of the residuals. Conclusions: The C-RC-QOL scale is reliable, valid and responsive for the evaluation of Chinese-speaking patients with RC disorders and it would be an effective instrument.