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Effect of Physical Activity on Functional Performance and Knee Pain in Patients With Osteoarthritis

Mansournia, Mohammad Ali and Danaei, Goodarz and Forouzanfar, Mohammad Hossein and Mahmoodi, Mahmood and Jamali, Mohsen and Mansournia, Nasrin and Mohammad, Kazem (2012) Effect of Physical Activity on Functional Performance and Knee Pain in Patients With Osteoarthritis. Epidemiology, 23 (4). pp. 631-640. ISSN 1044-3983

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Abstract

Background: A previous analysis of the Osteoarthritis Initiative study reported a dose-response relationship between physical activity and improved physical function in adults with knee osteoarthritis, using conventional statistical methods. These methods are subject to bias when confounders are affected by prior exposure. Methods: We used baseline and 1-, 2-, and 3-year follow-up data from the Osteoarthritis Initiative study of 2545 US adults with knee osteoarthritis recruited between 2004 and 2006 from 4 clinical sites. Physical activity was measured using the Physical Activity Scale for the Elderly, and outcomes were functional performance measured by the timed 20-meter walk test and self-reported knee pain measured by the Western Ontario and McMaster Universities Osteoarthritis Index. We estimated the effect of physical activity on each outcome using inverse probability-weighted (IPW) estimators of marginal structural models. For each outcome, we fitted 2 separate IPW models adjusting for concurrent or lagged confounders. Results: The mean differences in walking speed for the second, third, and fourth quartiles of physical activity relative to the first were 0.48 (95% confidence interval = -0.12 to 1.08), 0.45 (-0.23 to 1.13), and 0.46 (-0.29 to 1.22) meters/min based on the IPW model adjusting for concurrent confounders. When adjusting for lagged confounders, the results were 1.35 (0.64 to 2.07), 1.33 (0.54 to 2.14), and 1.26 (0.40 to 2.12). Both IPW models indicated that physical activity did not affect knee pain. Conclusions: Physical activity has no effect on knee pain and may have either a very small effect or no effect on functional performance in adults with knee osteoarthritis. Knee osteoarthritis is a leading cause of pain and disability in the elderly.1 There is no cure for osteoarthritis, and treatment is generally aimed at reducing pain and maintaining function.2 Several systematic reviews of randomized trials have demonstrated that exercise programs reduce pain and disability in the short term in patients with knee osteoarthritis.3–5 However, prospective observational studies are needed to evaluate the long-term effects of lifestyle physical activity among people with knee osteoarthritis. Using generalized estimating equations (GEE) to estimate a linear model, Dunlop et al 6 evaluated the effect of physical activity on subsequent 1-year functional performance in adults with knee osteoarthritis using 2-year follow-up data from the Osteoarthritis Initiative. The authors adjusted for the potential confounders available only at baseline, as well as the concurrent values of time-dependent confounders, and reported a dose-response relationship between physical activity and improved performance. However, standard methods for analysis of longitudinal data may lead to biased estimates when exposure affects a confounder, or when exposure is affected by prior outcome and affects future outcome.7–9 Both of these conditions are possible in the Osteoarthritis Initiative data, eg, physical activity may affect body mass index as a potential confounder and may also affect as well as be affected by functional performance. Marginal structural models overcome this problem by using inverse probability weighting.10,11 The aim of this study was to estimate the effect of physical activity on functional performance and knee pain in the Osteoarthritis Initiative cohort using inverse probability-weighted (IPW) estimators of marginal structural models.

Item Type: Article
Subjects: QS Human Anatomy
Divisions: Faculty of Medicine, Health and Life Sciences > School of Medicine
Depositing User: ePrint Admin Admin
Date Deposited: 22 Jun 2013 08:14
Last Modified: 22 Jun 2013 08:41
URI: http://eprints.ajaums.ac.ir/id/eprint/16

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