Is there an increased risk of knee osteoarthritis among farmers? A population-based case-control study

Occupational workload is generally considered a to be contributing cause in the development of knee osteoarthritis, in addition to well-known risk factors such as age, female gender, excess weight and previous knee injuries. Farmers have an increased risk of developing hip osteoarthritis, but it is uncertain if farming is influencing the occurrence of knee osteoarthritis. The aim of this population-based case-control study was to investigate the risk of radiographically verified femorotibial osteoarthritis among farmers and those in some other physically demanding occupations. A mailed questionnaire inquiring about previous occupations was answered by 778 subjects having X-ray verified osteoarthritis in the femorotibial joint and 695 matched controls. The reply frequency was 89%. Mean age of the participants was 63 years, 43% were male and 57% female. The relationship between knee osteoarthritis and occupation was analysed by multiple logistic regression, with adjustment for a number of variables. Men who had worked for 11-30 years in the building and construction industry had a 3.7-times (95% CI 1.2-11.3) increased risk of knee osteoarthritis. Farm work was not related to an increased risk for men. However, women who had worked for 11-30 years in farming tended to have an increased risk (OR 2.1, 95% CI 1.0-4.5). Forestry, letter-carrying (postal), cleaning and healthcare work was not related to knee osteoarthritis. Excess weight, heredity and previous knee injuries were strong risk factors, whereas smoking showed a negative relationship to knee osteoarthritis. Work in building and construction occupations, but not in farming, was associated with an increased risk of knee osteoarthritis.