Factors associated with functional impairment in symptomatic knee osteoarthritis

Objectives. Knee osteoarthritis (OA) is a major cause of disability, partic ularly in the elderly. The factors determining disability remain unclear. T he 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 obser ved variance in self-reported disability. Methods. The subjects (n = 69) were hospital out-patients. Self-reported di sability was measured by the Western Ontario and McMaster Universities (WOM AC) OA index. Pain was measured by the WOMAC and the McGill pain questionna ire. 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 s cored for individual features. Results. Pain severity, obesity and helplessness were the most important de terminants of disability: a model including these variables accounted for 5 9.9% variance in WOMAC disability. Anxiety remained associated with disabil ity 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 st udy provides further support for interventions targeting anxiety and helple ssness in knee OA.