Occupational kneeling and radiographic tibiofemoral and patellofemoral osteoarthritis

The objective of our study was to evaluate the association between occupational kneeling and compartment specific radiographic tibiofemoral (TF) and patellofemoral (PF) osteoarthritis (OA).

Questionnaire data and bilateral knee radiographs were obtained in 134 male floor layers and 120 male graphic designers (referents). Weight-bearing radiographs in three views (postero-anterior, lateral and axial) were classified according to joint space narrowing. After the exclusion of subjects with reports of earlier knee injuries the odds ratio (OR) with 95% confidence intervals (CI) of TF and PF OA was computed among floor layers compared to graphic designers in three age groups (/= 60 years). Using logistic regression, estimates were adjusted for body mass index and knee-straining sports. In addition, the association between trade seniority and TF OA was assessed in age-adjusted test for trend analyses.

The prevalence of TF OA was significantly higher among floor layers aged 50-59 years compared to graphic designers (OR = 3.6, 95% CI = 1.1-12.0) while non-significant estimates were found in the young and elderly age groups. Furthermore, the adjusted OR of TF OA increased with trade seniority among floor layers (test for trend, OR = 2.2, 95% CI = 1.0-5.1), but not among graphic designers (OR = 1.2, 95% CI = 0.4-3.5). There were no significant differences regarding PF OA between the two occupational groups.

Results corroborate the existence of a causal relationship between occupational kneeling and radiographic TF OA and suggest a dose-response association with trade seniority. An association between kneeling and PF OA was however doubtful. Apparent discrepancies between findings in different age groups are most likely reflecting selection bias.