Physical functional dimension scales are an alternative to condition-specific health status measures

Objective: The objective was to examine whether one could develop clinically useful scales representing functional dimensions out of the item pool of the condition-specific instrument WOMAC (Western Ontario and McMaster Universities Osteoarthritis Index). Design: The exploratory analysis was done with a test set from a clinical cohort study of patients with OA of the lower extremities undergoing a comprehensive rehabilitation. The analysis was performed with descriptive methods and factor analysis. To validate the physical functional scales we examined their performance in OA patients undergoing a randomized controlled trial with chondroitin-sulfate, Results: 121 patients were included in the test set, 302 patients in the validation set. The analysis revealed physical functional dimension scales including items asking about bending, walking/standing, rest activities and ascending/descending. With one exception the results could be replicated in the validation set. Conclusions: Deficits in the the lower extremities function of OA patients can be described by scales. The approach is psychometrically sound and may better represent the characteristics of the condition. Further studies should evaluate whether the use of these scales will result in improved responsiveness and whether they are more useful for clinical practice than the entire condition specific index.