Contribution of Psychosocial and Mechanical Variables to Physical Performance Measures in Knee Osteoarthritis

BACKGROUND AND PURPOSE: This cross-sectional study evaluated the relative contributions of psychosocial and mechanical variables to physical performance measures in people with knee osteoarthritis (OA). SUBJECTS: Fifty-four subjects (age, in years: mean=68.3, SD=8.7, range=50-87) with radiographically confirmed knee OA were included in this study. METHODS: Physical performance measures included the Six-Minute Walk Test (SMW), the Timed "Up & Go" Test (TUG), and a stair-climbing task (STR). Responses to psychosocial questionnaires that reflect depression, anxiety, and self-efficacy (a person's confidence in his or her ability to complete a task) were collected. Mechanical variables measured included body mass index and knee strength (force-generating capacity of muscle). Stepwise linear regressions were performed with the SMW, TUG, and STR as separate dependent variables. RESULTS: Functional self-efficacy explained the greatest amount of variance in all performance measures, contributing 45% or more. Knee strength and body weight also explained some variance in performance measures. Anxiety and depression did not explain any variance in performance. DISCUSSION AND CONCLUSION: Physical therapists evaluating the significance of the SMW, TUG, and STR scores in subjects with knee OA should note that a large part of each score reflects self-efficacy, or confidence, for physical tasks, with some contributions from knee strength and body weight.