Predictive value of the Western Ontario and McMaster Universities Osteoarthritis Index for the amount of physical activity after total hip arthroplasty

BACKGROUND AND PURPOSE Despite the recognized health benefits of physical activity, little is known about the amount of physical activity that patients perform after total hip arthroplasty (THA). To this end, the ability of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) to predict the amount of physical activity that patients with a THA perform, as measured by the Short Questionnaire to Assess Health-Enhancing Physical Activity (SQUASH), was determined. SUBJECTS AND METHODS Three hundred sixty-four patients who had a THA returned questionnaires. Pearson correlation coefficients were calculated between scores on the WOMAC and SQUASH. Binary logistic regression modeling was used to determine the extent to which the WOMAC score could predict that patients would meet national and international guidelines for health-enhancing physical activity. RESULTS Scores on the WOMAC and SQUASH showed a significant, but low, correlation (r=.14-.24). Although the WOMAC score was a significant predictor for meeting national and international guidelines for physical activity, the odds ratio was low (1.022, 95% confidence interval=1.012-1.033) and only 6.9% of the variance could be explained (Nagelkerke r(2)=.069). DISCUSSION AND CONCLUSION The results suggest that the WOMAC is not suitable for predicting the amount of physical activity after THA, requiring the use of an additional outcome measure.