The objectives of this study were to examine which factors, according to the International Classification of Functioning, Disability and Health (ICF) framework contribute to the explanation of activity limitations measured by the Health Assessment Questionnaire (HAQ - model I) and which factors contribute to the explanation of participation restrictions measured by the Social Function Scale of SF-36 (model II) in patients with rheumatoid arthritis (RA).
Cross-sectional data collection of variables concerning the health status of 239 consecutively included patients with RA at the outpatient Departments of Physical Medicine and Rehabilitation of the University Hospital of Zurich and of the University Hospital of Munich was conducted. Measures included: disease activity score (DAS-28), Rheumatoid Arthritis Disease Activity Index (RADAI), HAQ, Short-form-36 (SF-36), Sociodemo-graphy Questionnaire, Comorbidity Questionnaire (SCQ), Muscle Strength Index (MSI), range of motion (EPM-ROM), grip strength, Sequentional Occupational and Dexterity Assessment (SODA), radiologic score (Ratingen Score). Multivariate regression analyses were conducted building models of explanation.
Model I included vitality, RADAI, DAS, SODA PAIN Score, MSI and EPM-ROM as explaining variables with a globally explained variance of 53%. Model II included vitality, mental health, the HAQ and living alone as explaining variables with a globally explained variance of 42.4%.
Activity limitations in RA were mainly explained by vitality and disease activity factors. Restrictions in participation in RA were mainly explained by vitality and mental health.