Western Ontario Osteoarthritis of the Shoulder Index (WOOS) - a validation for use in proximal humerus fractures treated with arthroplasty

BACKGROUND: The Swedish shoulder and Arthroplasty Registry (SSAR) use the Western Ontario Osteoarthritis of the Shoulder Index (WOOS) as their shoulder-specific score in the follow-up. WOOS is not yet validated for use as the Patient Reported Outcome Measurement (PROM) for proximal humerus fractures (PHF) treated with shoulder hemiarthroplasty (SHA) in the Swedish registry. The aim of this study was to examine the validity, the reliability and the responsiveness of WOOS as a PROM for proximal humerus fractures treated with shoulder arthroplasty. METHODS: Data was collected from the SSAR from the 1(st) of January 2008 to the 31(st) of June 2011. A total of 72 subjects were identified with at least 1 year of follow-up. Of these 43 completed all the shoulder-specific PROM together with a clinical examination, including a WOOS retest and general health scores. A group of 29 did not undergo any clinical examination, but they completed all the questionnaires not requiring a clinical examination. The validity was assessed with WOOS compared to satisfaction level, and the Spearman rank coefficient was used for the correlation between WOOS and the shoulder-specific scores (Constant-Murley Score, Oxford Shoulder Score, American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form and EQ-5D. For reliability, Intra Class Correlation (ICC) was used for the test–retest assessment and Cronbach´s alpha for the construct reliability. RESULTS: The validity for WOOS had an excellent correlation (> 0.75) with all the shoulder-specific scores and a good correlation (> 0.6) with EQ-5D. The reliability with the test–retest of the total WOOS score and the subgroups had an excellent correlation. Cronbach´s alpha also supports the construct of WOOS. There were no floor or ceiling effects. CONCLUSIONS: We found that WOOS is a reliable tool for evaluating patients with SHA after PHF. Based on our study, we recommend the continued use of WOOS in shoulder arthroplasty registries and observational studies.