Factors associated with functional impairment in symptomatic knee osteoarthritis

Objectives. Knee osteoarthritis (OA) is a major cause of disability, particularly in the elderly. The factors determining disability remain unclear. The aim of this study was to assess the impact of clinical and psychosocial variables on function in knee OA and to develop models to account for observed variance in self-reported disability. Methods. The subjects (n = 69) were hospital out-patients. Self-reported disability was measured by the Western Ontario and McMaster Universities (WOMAC) OA index. Pain was measured by the WOMAC and the McGill pain questionnaire. Depression, anxiety, helplessness, self-efficacy, fatigue and quality of life were measured by standard instruments. A detailed knee examination, including pain threshold by dolorimetry, was performed. Radiographs were scored for individual features. Results. Pain severity, obesity and helplessness were the most important determinants of disability: a model including these variables accounted for 59.9% variance in WOMAC disability. Anxiety remained associated with disability in some models. Disability was unrelated to radiographic change. Conclusions. Function in symptomatic knee OA is determined more by pain and obesity than by structural change, at least as seen on plain X-ray. Our study provides further support for interventions targeting anxiety and helplessness in knee OA.