Objective: To determine the minimal perceptible clinical improvement (MPCI) in patients with osteoarthritis (OA) with the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire, and patient and investigator global assessment of disease status in randomized clinical trials for treatment of OA.
Methods: Subjects with OA of the knee or hip were randomized to receive either rofecoxib 12.5 or 25 mg once daily, ibuprofen 800 mg 3 times daily, or placebo for 6 weeks. The WOMAC and global assessments were completed at baseline and Weeks 2, 4, and 6. A patient global assessment of response to therapy (0 to 4 scale) was used to "anchor" the WOMAC scores. MPCI was defined as the difference in mean change from baseline in WOMAC (100 mm normalized visual analog scale, VAS) between patients with 0 = "None" global response to therapy and patients with 1 = "Poor" global response to therapy.
Results: MPCI was determined to be 9.7, 9.3, and 10.0 mm for the WOMAC pain, physical function and stiffness subscales, respectively, and 11.1 mm for WOMAC question 1: Pain walking on a flat surface. The MPCI for the investigator was 0.4 with investigator assessment of disease status reported on a 0 to 4 Likert scale. Of note, the estimated MPCI for the WOMAC and investigator globals were similar irrespective of treatment, sex, age, or geographic region.
Conclusion: In this analysis, mean changes of roughly 9 to 12 mm (100 mm normalized VAS) on WOMAC scales were perceptible changes to patients with hip and knee OA. A mean decrease of 0.4 in global disease status (0 to 4 Likert scale) as assessed by the investigator corresponded to the patients' MPCI. Understanding the minimal perceptible differences may permit a better assessment of the clinical relevance of therapeutic interventions in OA.