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Cumulative occupational physical load as a risk factor for knee osteoarthritis in men and women Ezzat, Allison Mairi


Objective: To determine the association between cumulative occupational physical load (COPL) to the knee and the presence of symptomatic osteoarthritis (SOA) and magnetic resonance imaging–defined osteoarthritis (MRI-OA). Methods: Cross-sectional analyses of symptomatic and asymptomatic (n=327) individuals were performed. Inclusion criteria for the symptomatic participants were: 1) having pain, aching, or discomfort in or around the knee on most days of the month at any time in the past; 2) having any pain, aching, or discomfort in or around the knee in the past 12 months. Asymptomatic participants responded “no” to both knee pain questions. COPL was calculated using a self-reported level of activity (five levels) and participation in knee bending/kneeling tasks (three levels) for each occupation held. SOA was defined by the Kellgren Lawrence x-ray grade ≥2, plus the presence of knee pain, as defined by the study inclusion pain criteria. MRI-OA was defined using the criteria specified by Hunter and associates. Logistic regression analyses, adjusted with population weights, were used to examine the associations between COPL (reference group=the lowest COPL quarter) and the presence of SOA and MRI-OA, respectively, after controlling for age, female sex, body mass index, and two-way interactions. Results: Participants (women=167, men=160) were on average 58.5 (SD=11.0) years old with a BMI of 26.3 (SD=4.7). Of those, 102 (31.2%) participants had SOA. For SOA, a monotonic statistically significant relationship was found between COPL 4 (highest quarter; odds ratio (OR)=8.16; 95% CI=1.89, 35.27) and COPL 3 (OR=5.73; 95% CI=1.36, 24.12) versus COPL 1. For MRI-OA, monotonic and statistically significant associations were found in COPL 4 versus 1 (OR=9.54; 95% CI=2.65, 34.27); COPL 3 versus 1 (OR=9.04; 95% CI=2.65, 30.88); COPL 2 versus 1 (OR=7.18; 95% CI=2.17, 23.70). Conclusion: COPL is a significant risk factor for knee OA. Dose response relationships between COPL and both SOA and MRI-OA were found. This study provides new insight into the role of occupation in knee OA, although the results should be interpreted cautiously due to limitations associated with the cross-sectional study design.

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