Can the western Ontario and McMaster Universities (WOMAC) osteoarthritis index be used to evaluate different hip joints in the same patient?

The Western Ontario and McMaster Universities (WOMAC) osteoarthritis index was originally designed for disease-specific evaluation of patients with lower extremity osteoarthritis (1988), but has not been validated for evaluation of more than one joint at the same time in the same patient. Thirty-three patients with bilateral total hip arthroplasties answered a questionnaire containing both the WOMAC osteoarthritis index and the Harris hip score (HHS) (1969), a joint-specific health status measure that was designed to include evaluation of bilateral hip arthroplasty. Differences in scores between hips were highly correlated for HSS and WOMAC total score (P = .0001), HHS pain and WOMAC pain subscores (P = .0001), and HHS function and WOMAC physical function subscores (P = .0001). WOMAC stiffness and HHS range of motion were not significantly correlated (P = .1308). In 23 patients (70%), both scores graded the hips with the same comparative outcome. When comparative outcomes were different, the average difference was less than 3 points (of 100 possible points). These results demonstrate that patients with bilateral hip arthroplasty can apply the WOMAC osteoarthritis index questions to individual hips at the same time as effectively as the joint-specific HHS questions.