Introduction Knee osteoarthrosis is characterised by pain and increasing disability with impact on life quality and ability to work. The work of baggage handlers is characterised by daily heavy lifting in a standing or kneeling/squatting position.

Aims To evaluate the impact of employment as baggage handler on the incidence of knee osteoarthrosis.

Methods A follow-up study based on the Copenhagen Airport Cohort consisting of male baggage handlers employed at Copenhagen Airport and a reference group of unskilled men followed from 1990 to 2012. Exposure was expressed as cumulative years of employment as a baggage handler. The cohort was followed in the National Patient Register to obtain information on diagnoses and surgery. Outcome was first hospital admission with diagnosed knee osteoarthrosis and/or knee replacement.

Results The cohort contained 3,442 baggage handlers and 65,511 workers in the reference group. For the baggage handlers the unadjusted incidence rate ratio (IRR) of knee osteoarthrosis increased with longer cumulative years of employment. The same pattern of associations was found in the adjusted analyses, but only statistically significant for baggage handlers with the highest seniority. Because age and seniority are highly correlated, additional analyses were made. We found that the association between age and osteoarthrosis among baggage handlers was stronger (IRR = 2.09; 95% CI: 1.68–2.60) compared to the reference group (IRR = 1.58; 1.53–1.63) and test for interaction was significant (P = 0.01) indicating that an increased incidence of knee osteoarthrosis was obtained at a younger age among baggage handlers compared to the reference group.

Discussion The risk of developing knee osteoarthrosis increased with cumulative years as a baggage handler, but after adjustment for age the association was no longer significant. However, the true effect of cumulative exposure may be underestimated because of an over-adjustment for age, since baggage handlers got knee osteoarthrosis at younger ages than the reference group.