Objective: To evaluate the association between occupations, sports, life-long daily activities, and knee osteoarthritis.
Methods: In this case-control study, we randomly recruited 480 subjects with knee osteoarthritis, who had participated in the first stage of a community-based study in Tehran, and compared them with 490 controls. A questionnaire was used to record all occupations, sports, and the details of 10 daily activities. The mean +/- SD hours/day spent on these activities were calculated and compared using the lightest activity as reference. Generalized estimation equation was used with each knee as the unit of analysis.
Results: The mean +/- SD age and percentage of female distribution was 57 +/- 12 years, 69.8% women for cases, and 46.8 +/- 15 years, 64.1% women for controls. After adjusting for age, sex, and body mass index, 2 activities were risk factors for knee osteoarthritis: prolonged squatting (odds ratio [OR] 1.51, 95% confidence interval [95% CI] 1.12-2.04) and cycling (OR 2.06, 95% CI 1.23-3.45). Knee-bending had borderline significance (OR 1.98, 95% CI 0.98-3.99). Carrying loads (OR 1.24, 95% CI 0.87-1.76) or climbing stairs (OR 0.99, 95% CI 0.69-1.42) showed no extra risk for knee osteoarthritis. Prolonged standing, sitting on the floor, and walking up/downhill were not risks for knee osteoarthritis. Housewives were at greater risk (borderline-significant) of developing knee osteoarthritis (OR 1.68, 95% CI 0.93-3.03) than women whose main occupation was outside the home. Other types of jobs and sports did not show an extra risk of knee osteoarthritis.
Conclusion: Our findings support the role of lifestyle in the pathogenesis of knee osteoarthritis for squatting and cycling. Education on preventable risk factors should be considered in order to ensure people use knee joints appropriately and avoid overuse.