Validity, reliability, and responsiveness of the Swedish version of Western Ontario Osteoarthritis of the Shoulder index

BACKGROUND: The Western Ontario of the Shoulder index (WOOS) is a patient-reported, disease-specific instrument, designed to measure quality of life in patients with osteoarthritis of the shoulder. The Swedish Shoulder Arthroplasty Registry (SSAR) uses WOOS and EuroQoL 5-dimensions 3 levels (EQ-5D-3L) as patient reported outcome measures. The purpose of this study was to test the validity, responsiveness, and reliability of the Swedish translation of WOOS for patients with osteoarthritis of the shoulder. METHODS: Data was collected from three shoulder arthroplasty studies performed during 2005–2013, with 23, 21, and 19 patients respectively. Forms were collected preoperatively, and postoperatively between 12 and 24 months. WOOS and EQ-5D-3L were used in all three studies. Additionally, the Oxford Shoulder Score (OSS) (n = 23) was used in one study, and the Constant-Murley score (CMS) (n = 40) in two of the studies. Validity was analysed by calculating Pearson’s correlation coefficient (PCC). Cronbach’s alpha (CA) was used to estimate internal consistency and reliability. The responsiveness of WOOS was measured by calculating effect size and standardized response mean. To assess the performance of WOOS over time, we present repeated measures of WOOS in the registry over a 10-year period. RESULTS: The validity analysis showed excellent correlations of WOOS to CMS, OSS and EQ-5D 3L, with Pearson’s correlation coefficient of 0.72, 0.83, and 0.62 respectively (P < 0.001). There were adequate floor effects in the sport and lifestyle domains preoperatively, and adequate ceiling effects in all domains postoperatively. There were no floor effects and adequate ceiling effects for total WOOS. Analyzing reliability, Cronbach’s alpha was 0.95 for the pre- and postoperative WOOS scores combined. The analysis of responsiveness for WOOS showed an effect size of 2.52 and a standardized response mean of 1.43. The individual results measured by WOOS within the registry shows stable levels from 1 to 10 years. CONCLUSION: The Swedish translation of WOOS is valid, reliable, and responsive for use in a clinical setting for patients with glenohumeral osteoarthritis treated with shoulder arthroplasty, and we regard it as an appropriate instrument for use in the Swedish Shoulder Arthroplasty Registry.