title: Are daily physical activities risk factors for knee osteoarthritis?
abstract: OBJECTIVE
  In spite of many epidemiologic studies, there is still insufficient evidence on the effects of daily physical activity on osteoarthritis. The purpose of this study was to evaluate the association between squatting, climbing, kneeling, lifting and carrying weights and knee osteoarthritis.
  
  
  METHODS
  This population-based case control study was the second stage of the World Health Organization - Community Oriented Program for Control of Rheumatic Diseases (WHO-COPCORD), in which 263 cases and 263 controls aged 30-70 years were selected from 780 eligible cases and 4373 eligible controls identified in the first-stage survey in Tehran. Demographic and lifestyle data were obtained from all the participants. The selection probability of each case and control and the stabilized weight was estimated using the restricted cubic spline models. Multivariable regression models by inverse probability weighting were used to minimize the effect of the bias resulting from the unequal selection probability.
  
  
  RESULTS
  The female sex, age, obesity and history of previous severe knee injury maintained their strong and significant associations with knee osteoarthritis before and after the adjustment. Although walking and squatting were significantly different in the case and control groups in the bivariate analysis, after adjustment and weighting no such association was found between the disease and squatting, kneeling, standing, walking, climbing, carrying and lifting.
  
  
  CONCLUSIONS
  This study did not show any significant association between knee osteoarthritis and daily occupational and non-occupational activities; nevertheless it does add another piece of information to the literature on the complex role of physical activities in knee osteoarthritis.
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Jaleh
authors.initials: J
authors.lastname: Gholami
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Mohammed-Ali
authors.initials: MA
authors.lastname: Mansournia
authors.affiliation: Rheumatology Research Center, Shariati Hospital, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Fereydoun
authors.initials: F
authors.lastname: Davatchi
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Kazem
authors.initials: K
authors.lastname: Mohammad
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Hamed
authors.initials: H
authors.lastname: Hosseini
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran.|Knowledge Utilization Research Center, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Reza
authors.initials: R
authors.lastname: Majdzadeh
mesh_terms: D000203:Activities of Daily Living; D000328:Adult; D000368:Aged; D001696:Biomechanical Phenomena; D016022:Case-Control Studies; D015444:Exercise; D005260:Female; D006306:Health Surveys; D006801:Humans; D007492:Iran / Q000453:epidemiology; D007719:Knee Joint / Q000503:physiopathology*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D009790:Occupations; D016017:Odds Ratio; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000453:epidemiology* / Q000503:physiopathology; D015995:Prevalence; D012307:Risk Factors
keywords: case-control study; inverse probability weighting; knee osteoarthritis; physical activity