J Haxby Abbott, Catherine Hobbs, David Gwynne-Jones

Study Design Clinical measurement study; secondary analysis of randomized clinical trial data. Background A 12-item reduced-item version of the Western Ontario and McMaster (WOMAC), a condition-specific, patient-reported osteoarthritis index, has been derived, published and validated. The minimum important change (MIC) of the ShortMAC has not been reported, or compared with the traditional 24-item WOMAC. Objectives To investigate the MIC of the 12-item ShortMAC and the traditional 24-item WOMAC across 3 levels of patient-perceived global change. Methods The MOA Trial cohort of 206 consecutive patients with knee or hip osteoarthritis were assessed at the initial visit and after 9 weeks of physical therapy (n=155) or usual medical care (n=51). The Global Rating of Change (GROC) instrument, assessed at the 9-week visit, provided the anchor. MIC was calculated, using receiver operating characteristic curve methodology, for the ShortMAC and the traditional WOMAC, across 3 levels of patient-perceived change (small, medium, large change) defined by the GROC. Results The MIC for the ShortMAC and traditional WOMAC (both transformed to a scale 0-100) was 7.9 and 9.8 points for small change, and 8.4 and 9.8 points for the medium change, and for 12.1 and 10.1 points for large change, respectively. The MIC of the pain and function subscales are also reported for small, medium, and large change. Conclusion The lower point estimates for MIC of the ShortMAC compared with the traditional WOMAC at conventional definitions of MIC, and half the number of items, indicate greater efficiency for use in clinical trials and reduced patient burden. J Orthop Sports Phys Ther, Epub 21 Oct 2017. doi:10.2519/jospt.2018.7676.