RESEARCH ARTICLE Open Access Background benefit from treatments or, indeed, identify those that

Full list of author information is available at the end of the articleOsteoarthritis (OA) is the most common cause of dis-ability in the UK [1] and with an aging population ever more treatments and procedures are being carried out. The increase in the number of treatments and proce-dures combined with limited resources means it is even more important to use accurate measures of outcome. Without good measures we cannot identify those that do not benefit from treatments, such as joint replace-ment, and for whom possibly other less invasive treat-ments may be more appropriate. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC [2]) is the most com-monly used disease-specific measure of outcome used in OA [3]. The WOMAC was based on the objective of defining the dimensionality of pain and disability i