EpidemiologyVolume 23, Issue 4, July 2012, Pages 631-640

Effect of physical activity on functional performance and knee pain in patients with osteoarthritis : Analysis with marginal structural models(Article)

  • aSports Medicine Research Center, Tehran University of Medical Sciences, Tehran, Iran
  • bDepartment of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, PO Box: 14155-6446, Tehran, Iran
  • cDepartment of Global Health and Population, Harvard School of Public Health, Boston, MA, United States
  • dInstitute for Health Metrics and Evaluation, University of Washington, Seattle, WA, United States
  • eAerospace Medical Research Unit, Department of Physiology, McGill University, Montreal, QC, Canada
  • fDepartment of Endocrinology, AJA University of Medical Sciences, Tehran, Iran


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. © 2012 by Lippincott Williams & Wilkins.

Indexed keywords

EMTREE medical terms:adultagedarticlefemalefollow uphumanknee osteoarthritisknee painlongitudinal studymaleoutcome assessmentperformancephysical activitypriority journalrating scaleself reportwalkingwalking speed
MeSH:AgedCausalityConfounding Factors (Epidemiology)ExerciseExercise TestFemaleFollow-Up StudiesHousekeepingHumansLeisure ActivitiesMaleMiddle AgedModels, StatisticalOsteoarthritis, KneePain MeasurementProspective StudiesSelf ReportTreatment OutcomeWalkingWork
  • ISSN: 10443983
  • Source Type: Journal
  • Original language: English
  • DOI: 10.1097/EDE.0b013e31824cc1c3
  • PubMed ID: 22415107
  • Document Type: Article

  Mansournia, M.A.; Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, PO Box: 14155-6446, Iran; email:[email protected]
© Copyright 2012 Elsevier B.V., All rights reserved. © MEDLINE® is the source for the MeSH terms of this document.


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