Linking osteoarthritis-specific health-status measures to the International Classification of Functioning, Disability, and Health (ICF)

Objectives: The objective of this study was to link the Western Ontario and McMaster Universities (WOMAC) and Lequesne-Algofunctional indices to the ICF on the basis of linking rules developed specifically to accomplish this aim. The linking process enables the understanding of the relationship between health-status measures and the ICF. Methods: Since the fifth World Health Organisation/International Liege Against Rheumatism (WHO/ILAR) Task Force and the Outcome Measures in Rheumatology Clinical Trials (OMERACT) group recommend the use of WOMAC and the Lequesne-Algofunctional indices in patients with osteoarthritis of the hip and knee in clinical trials, these two health-status measures have been used in this study. Both health-status measures were linked to the ICF separately by two trained health professionals. Consensus between health professionals was used to decide which ICF category should be linked to each item/concept of the two questionnaires. To resolve disagreements between the two health professionals, a third person trained in the linking rules was consulted. Results: Except for the concept of ‘morning stiffness’, both health professionals agreed on the ICF category chosen to link all the items/concepts of both questionnaires. Altogether, 29 different ICF categories have been linked. Five ICF categories belong to the ICF component ‘body functions’, 23 categories to the component ‘activities and participation’, and one category to ‘environmental factors’. Both questionnaires have 10 ICF categories in common. Conclusions: The results of the linking process reflect both the structure of the two questionnaires studied and the relationship between them, showing that the ICF classification can become the cardinal reference for existing health-status measures.