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Objective

To determine the associations between cumulative occupational physical load (COPL) and 3 definitions of knee osteoarthritis (OA).

Methods

Cross-sectional analyses were performed from 2 population-based cohorts (n = 327). Eligible symptomatic participants were those with pain, aching, or discomfort in or around the knee on most days of a month at any time in the past and any pain in the past 12 months. Asymptomatic participants responded “no” to both knee pain questions. Self-reported COPL was calculated over each participant's lifetime and then categorized into quarters (QCOPL). Radiographic OA (ROA) and symptomatic OA (SOA) were defined by Kellgren/Lawrence grade ≥2, with SOA also including pain. Magnetic resonance imaging (MRI) OA was defined using criteria by Hunter et al. Logistic regression, adjusted with population weights, examined the associations between QCOPL and each of ROA, SOA, and MRI-OA after controlling for covariates and two-way interactions.

Results

Participants had a mean ± SD age of 58.5 ± 11.0 years and a mean ± SD body mass index of 26.3 ± 4.7 kg/m2. Of those, 109 (33.3%) had ROA, 102 (31.2%) had SOA, and 131 (40.1%) had MRI-OA. Compared with QCOPL-1, increased odds of ROA were found for QCOPL-4 (odds ratio [OR] 3.15, 95% confidence interval [95% CI] 1.02–9.70) and QCOPL-3 (OR 4.19, 95% CI 1.55–11.34). Statistically significant relationships were found in SOA (QCOPL-4: OR 8.16, 95% CI 1.89–35.27; QCOPL-3: OR 5.73, 95% CI 1.36–24.12) and MRI-OA (QCOPL-4: OR 9.54, 95% CI 2.65–34.27; QCOPL-3: OR 9.04, 95% CI 2.65–30.88; QCOPL-2: OR 7.18, 95% CI 2.17–23.70).

Conclusion

Occupational activity is associated with knee OA, with dose-response relationships observed in SOA and MRI-OA.