Physical workload and the risk of severe knee osteoarthritis.

OBJECTIVES This study investigated the impact of physical workload on the risk of severe knee osteoarthritis (OA) leading to knee arthroplasty. METHODS In this case-referent study, the cases were 55- to 75-year-old men (N=55) and women (N=226) who had undergone their first knee arthroplasty operation for primary knee OA in the Kuopio University Hospital in 1992-1993. The referents (N=524) were from the same source population and were matched with the cases for age and gender. Information on explanatory variables was obtained by a computer-assisted telephone interview. Exposure was assessed up to 49 years of age. RESULTS After adjustment for body mass index, knee injury and leisure-time physical activity, an increased relative risk of knee OA was found for a history of high physical workload. The odds ratio (OR) was 1.53 [95% confidence interval (95% CI) 0.42-5.56] for the men and 2.03 (95% CI 1.03-3.99) for the women as compared with those with low physical workload. With respect to generic risk factors, climbing already at a medium level of exposure was associated with an increased risk of knee OA among the men (OR 3.06, 95% CI 1.25-7.46) and kneeling and squatting was a risk factor for both genders. Of the different trades, agriculture, forestry, fishing, transportation, and traffic showed the highest risks of knee OA. CONCLUSIONS The results of this study agree with the hypotheses that heavy physical loading increases the risk of knee OA and that cumulative physical stress has a deleterious effect on the knee joint.