OP0049 A pooled index to assess severity of osteoarthritis of the hip or knee. performance in a randomised, double blind, multicenter, crossover clinical trial of diclofenac/misoprostol (arthrotec) compared to acetaminophen in patients with osteoarthritis of the hip or knee
Authors: T Pincus, T Sokka
Journal: Annals of the Rheumatic Diseases (2001)

<h3>Background</h3> A pooled index of various measures, such as the disease activity index (DAS) in rheumatoid arthritis, can provide advantages over individual measures to assess disease severity, analyse responses to therapy, and improve statistical power in a clinical trial or observational study. <h3>Objectives</h3> To apply an index of four measures of severity of osteoarthritis of the hip or knee, the Western Ontario McMaster (WOMAC) scale, visual analogue scale (VAS) for pain, Kellgren-Lawrence radiographic stage, and number of joints involved among two hips and two knees, in analyses of results of a randomised, controlled clinical trial of diclofenac/misoprostol (Arthrotec, ARTH) compared to acetaminophen (ACET). <h3>Methods</h3> 227 patients with radiographic stage 2–4 osteoarthritis of the hip or knee received either 6 weeks of ARTH 75 mg twice a day or ACET 1,000 mg four times a day after a washout period, and then the other drug for 6 weeks, in a randomised, double-blind, multicenter, crossover clinical trial. A pooled index to recognise patients who had mild osteoarthritis was developed according to 4 criteria: location in only one knee, Kellgren-Lawrence stage 2, lowest tertile at screening for the WOMAC, and lowest tertile at screening for the pain VAS. The value of the pooled index was 0 (mildest) if 3 or 4 of the indicators applied to a patient; the value was 1 if 2 indicators applied to a patient, 2 if only one indicator applied to a patient, and 3 (most severe) if no indicator applied to a patient. <h3>Results</h3> Overall, WOMAC pain scores were improved by 7.8 of 100 units (p &lt; 0.001), and pain VAS scores were improved by 14.6 of 100 units (p &lt; 0.001), while taking ARTH versus ACET. Differences between changes in WOMAC scores while taking ARTH versus ACET were -0.8 (advantage to ACET) for 26 patients with a pooled index of 0 (p = 0.86), compared to 1.5 (advantage to ARTH) for 50 patients with a pooled index of 1 (p = 0.70), 6.8 for 74 patients with a pooled index of 2 (p = 0.06), and 14.7 for 77 patients with pooled index of 3 (p &lt; 0.001). Differences between changes in pain VAS scores while taking ARTH versus ACET were 0.9 (advantage to ARTH) for patients with a pooled index of 0 (p = 0.88), compared to 8.8 for patients with a pooled index of 1 (p = 0.11), 14.0 for patients with a pooled index of 2 (p = 0.002), and 22.1 for patients with a pooled index of 3 (p &lt; 0.001). <h3>Conclusion</h3> A pooled index of four measures of severity of osteoarthritis of the hip or knee, the WOMAC, pain VAS, Kellgran-Lawrence radiographic stage, and number of joints involved can be applied to analyse results of a clinical trial, and may be useful to stratify patients in clinical trials and clinical care. <h3>Reference</h3> Goldsmith CH, Smythe HA, Helewa A. Interpretation and power of pooled index. J Rheumatol. 1993;20:575–8