Relationship between self-reported and performance-based tests in a hip and knee joint replacement population

Our objectives were: (1) to assess the relationship between self-reported measures (Western Ontario and McMaster University Osteoarthritis Index (WOMAC) and Medical Outcomes Study Short Form-36 (SF-36)) and a performance-based timed-up-and-go (TUG) test in a hip and knee joint replacement population and (2) to determine the predictors of postoperative functional status as measured by the 12-week WOMAC and TUG scores. We surveyed 200 patients undergoing primary hip or knee replacement surgery for demographic data and outcome scores at baseline and 12-week follow-up. There was a weak correlation between preoperative TUG scores and preoperative SF-36 physical function scores (r=-0.28, p<0.0001), SF-36 role-physical scores (r=-0.21, p=0.0022) and WOMAC (r=0.29, p<0.0001) scores. The relationship was stronger between the postoperative TUG scores and WOMAC scores (r=0.43, p<0.0001), SF-36 physical function scores (r=-0.39, p<0.0001) and SF-36 role-physical (r=-0.33, p<0.0001) scores. Significant predictors for the TUG test at 12-week follow-up were age (p=0.004) and preoperative TUG scores (p<0.0001). Given low-to-moderate relationship between self-reported and performance-based tools, both tests are needed to assess the true level of patient disability.