Determinants of self-report outcome measures in people with knee osteoarthritis

Objectives: To identify the determinants of self-report mobility measures in people with knee osteoarthritis (OA) and to compare self-report measures with physical performance. Design: Cross-sectional, prospective. Setting: Motor performance laboratory and human mobility research center. Participants: A convenient sample of 54 participants with medial compartment knee OA (32 women, 22 men; age 68.3+/-8.7y; range, 50-87y). Three participants were excluded because of the presence of lateral knee OA on radiographs. Interventions: Not applicable. Main Outcome Measures: Self-reports were recorded by using the Western Ontario McMaster Universities Osteoarthritis Index (WOMAC) and the Medical Outcomes Study 36-Item Short-Form Health Survey (SF-36). Performance measures included the six-minute walk test (6MWT), Timed Up & Go (TUG) test, and a standardized stair-climbing task (STR). Results: Stepwise linear regression analysis identified models that included pain, quadriceps and hamstrings strength, and depression to explain 62% to 73% of the variance in scores on the physical functioning subscale of the WOMAC and the SF-36. These self-report measures had a moderate relation (r range,.46-64) with performance measures (6MWT, TUG, STR). Conclusions: Self-report measures were strongly related to pain; physical performance measures were strongly related to self-efficacy. Regression models showed that self-report scores reflect pain, knee strength, and depression. The relation between self-report and performance measures was moderate, suggesting that these examine different aspects of mobility.