RELATIVE CONTRIBUTION OF PSYCHOSOCIAL AND MECHANICAL ATTRIBUTES TO THE PERFORMANCE OF PHYSICAL TASKS IN PEOPLE WITH KNEE OSTEOARTHRITIS. Monica Maly*1; Patrick Costigan2; Sandra Olney1 1. School of Rehabilitation Therapy, Queen's University, Kingston, ON, Canada; 2. School of Physical and Health Education, Queen's University, Kingston, ON, Canada PURPOSE: This cross-sectional study evaluated the relative contribution of psychosocial and mechanical variables to the performance of walking, stair-climbing and transferring in people with knee osteoarthritis (OA). Mechanical variables included knee strength and body weight. Psychosocial variables were the scores obtained from questionnaires of depression, anxiety and self-efficacy (one's confidence to complete a task). BACKGROUNDS/SIGNIFICANCE: Physical therapists provide interventions mainly targeted at improving mechanical characteristics like strength and body weight in people with knee OA. However, therapists note that psychosocial status also influences performance. Our goal was to examine the relative contributions of psychosocial and mechanical attributes to the performance of physical tasks to help identify what variables may have the greatest impact on performance and therefore guide treatment for people with knee OA. SUBJECTS: Fifty-four individuals, over age 50, with physician-diagnosed and radiographically confirmed knee OA participated (age 68.3 ± 8.7, range 50 - 87 years old). Thirty-two were female. Individuals with medical conditions that limited their ability to walk for six minutes, those with hip or ankle conditions and neurological conditions were excluded. Table 1 summarizes the characteristics of the subjects. METHODS AND MATERIALS: The performance outcome measures included the Six Minute Walk (SMW), Timed Up and Go (TUG) and a stair-climbing task (STR). Responses to the Centre for Epidemiological Studies-Depression scale, State Trait Anxiety Inventory and Arthritis Self-Efficacy scale were collected. The mechanical variables included body mass index and knee strength measured with the Biodex System 3 Isokinetic Dynamometer. The strength variables were the mean peak torques of five concentric quadriceps contractions and five hamstrings contractions recorded at 60°/s. ANALYSES: A step-wise linear regression was performed using SMW, TUG and STR as separate dependent variables. RESULTS: The Functional Self-Efficacy subscale was the single best explanatory variable of mobility, contributing 43% or more to the variance in all 3 outcome measures. By contrast, body mass index and strength explained no more than 5% each to the variance in performance measures. Anxiety and depression contributed little to the variance in the performance scores of the SMW, TUG or STR. The regression models are presented in Table 2. CONCLUSIONS: The Functional Self-Efficacy subscale was the single best explanatory variable of all performance scores. Obesity and strength explained a relatively small amount of variance. Physical therapists evaluating the significance of the SMW, TUG and stair-climbing scores in the OA knee population should note that a large part of each score reflects the individual's confidence to complete the mobility tasks. FUNDING SOURCE: Canadian Institutes of Health Research (Grant #99034), Toronto Rehabilitation Institute, Natural Sciences and Engineering Research Council. KEYWORDS: strength, obesity, self-efficacy, knee osteoarthritis, mobility Table 2: Step-Wise Linear Regression Models of Performance Outcome Measures *One subject did not complete the strength testing due to a medical event, related to asthma, causing fatigue (n=53). Table 1: Descriptive Data of Subject Characteristics *Pain, Stiffness and Physical Functioning subscales of the Western Ontario McMaster Universities Osteoarthritis Index. Data normalized to /100 for each subscale. †Gait speed recorded during Six Minute Walk. ‡Co-morbidities diagnosed by a physician that requires ≧3 months treatment, excluding knee OA. Copyright 2009 by the American Physical Therapy Association. Requests for reprints should be directed to the corresponding author of the article. Educators, students, and other academic customers may receive permission to reprint copyrighted material from Physical Therapy (ISSN 1538-6724) by contacting the Copyright Clearance Center Inc, 222 Rosewood Dr, Danvers, MA 01923. Other types of customers who want permission to reprint should contact the APTA Editorial Office, Attn: Physical Therapy.