Changes in outcome measures for impairment, activity limitation, and participation restriction over two years in osteoarthritis of the lower extremities

Objective To describe changes in outcome measures in patients with knee and hip osteoarthritis (OA) over 2 years according to the International Classification of Functioning, Disability and Health, and to evaluate the sensitivity to change of available outcome instruments. Methods A total of 115 symptomatic knee or hip OA patients (mean age 60.0 years, 80% women) were followed for 2 years. Standardized knee and hip radiographs were scored for joint space narrowing (JSN) using the Osteoarthritis Research Society International Atlas. Pain intensity in knees and hips was graded during physical examination. Self‐reported pain and functioning were assessed with the Western Ontario and McMaster Universities OA Index (WOMAC). Social functioning was assessed with social functioning scores of the RAND 36‐item Health Survey. Standardized response means (SRMs) were calculated to evaluate sensitivity to change. Results Substantial increases in JSN and pain intensity total scores over 2 years were observed (SRMs 0.43 and 0.41, respectively). Twenty‐three percent of patients had an increase of at least 1 point in JSN total scores. An increase in pain intensity total scores was present in 46% of patients, whereas a decrease was observed in 19.1.% of patients. WOMAC pain and function scores showed small increases (SRMs 0.15 and 0.18, respectively). No change was seen in social functioning scores (SRM 0.01). Conclusion Objective instruments measuring impairment in body structures and function are more sensitive to change over 2 years in patients with OA than self‐reported measurements of impairment in body function, activity limitation, and participation restriction. These findings encourage development of new instruments to improve measurement of disease outcome in OA.