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Evaluation of clinically relevant changes in patient reported outcomes in knee and hip osteoarthritis: the minimal clinically important improvement

F Tubach¹, P Ravaud¹, G Baron¹, B Falissard², I Logeart³, N Bellamy⁴, C Bombardier⁵, D Felson⁶, M Hochberg⁷, D van der Heijde⁸, M Dougados⁹

¹ Institut National de la Santé et de la Recherche Médicale (INSERM) E 0357; Département d’Epidémiologie, Biostatistique et Recherche Clinique; Groupe Hospitalier Bichat-Claude Bernard (Assistance Publique—Hôpitaux de Paris); Faculté Xavier Bichat (Université Paris 7), Paris, France
² Faculté de Médecine Paris-sud, Département de Santé Publique, Hôpital Paul Brousse (Assistance Publique—Hôpitaux de Paris), Villejuif, France
³ Merck, Sharp & Dohme Chibret Laboratories, Paris, France
⁴ Department of Medicine, University of Queensland, Royal Brisbane Hospital, Brisbane, Queensland, Australia
⁵ Institute for Work and Health, Toronto, Ontario, Canada
⁶ Boston University School of Medicine, Boston, Massachusetts, USA
⁷ University of Maryland, Baltimore, Maryland, USA
⁸ University Hospital, Maastricht, The Netherlands
⁹ Service de Rhumatologie B, Hôpital Cochin (Assistance Publique—Hôpitaux de Paris), Paris, France

Correspondence to:
Dr F Tubach
Département d’Epidémiologie, Biostatistique et Recherche Clinique, INSERM E0357, Hôpital Bichat, 46 rue Henri Huchard, 75018 Paris, France; florence.tubach{at}bch.ap-hop-paris.fr

Background: In clinical trials, at the group level, results are usually reported as mean and standard deviation of the change in score, which is not meaningful for most readers.

Objective: To determine the minimal clinically important improvement (MCII) of pain, patient’s global assessment of disease activity, and functional impairment in patients with knee and hip osteoarthritis (OA).

Methods: A prospective multicentre 4 week cohort study involving 1362 outpatients with knee or hip OA was carried out. Data on assessment of pain and patient’s global assessment, measured on visual analogue scales, and functional impairment, measured on the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC) function subscale, were collected at baseline and final visits. Patients assessed their response to treatment on a five point Likert scale at the final visit. An anchoring method based on the patient’s opinion was used. The MCII was estimated in a subgroup of 814 patients (603 with knee OA, 211 with hip OA).

Results: For knee and hip OA, MCII for absolute (and relative) changes were, respectively, (a) –19.9 mm (–40.8%) and –15.3 mm (–32.0%) for pain; (b) –18.3 mm (–39.0%) and –15.2 mm (–32.6%) for patient’s global assessment; (c) –9.1 (–26.0%) and –7.9 (–21.1%) for WOMAC function subscale score. The MCII is affected by the initial degree of severity of the symptoms but not by age, disease duration, or sex.

Conclusion: Using criteria such as MCII in clinical trials would provide meaningful information which would help in interpreting the results by expressing them as a proportion of improved patients.

Abbreviations: MCID, minimal clinically important difference; MCII, minimal clinically important improvement; NSAID, non-steroidal anti-inflammatory drug; OA, osteoarthritis; VAS, visual analogue scale; WOMAC, Western Ontario McMaster Universities Osteoarthritis Index

Keywords: Osteoarthritis; knees; hips; treatment response; outcome criteria; patient reported outcomes

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