Age, bodyweight, smoking habits and the risk of severe osteoarthritis in the hip and knee in men

Background: The objective of this study was to estimate the risk of severe osteoarthritis, with the need for arthroplasty, in the knee and/or hip according to body mass index (BMI) both within a normal range and in persons with high BMI. Furthermore, we wanted to study the significance of smoking. Methods: This study identifies male construction workers participating in a national health control program (n = 320,192). The incidence rate for joint replacement was found by matching with the Swedish hospital discharge register between 1987 and 1998. BMI and smoking habit was registered at the time of the health examination. Results: In total 1495 cases of osteoarthritis of the hip and 502 cases of osteoarthritis of the knee were identified and included in this analysis. The incidence rate was found to increase linearly to the BMI even within low and,normal' BMI. The relative risk for osteoarthritis of the hip was more than two times higher in persons with a BMI of 20-24 than in men with a BMI 17-19. There was almost a doubling of the risk of severe knee 2 osteoarthritis with an increase in BMI of 5 kg/m(2). Smoker had a lower risk of osteoarthritis than non-smokers and ex-smokers. Conclusions: BMI is an important predictor of osteoarthritis even within normal BMI. A decreased risk of osteoarthritis of the hip was found in smokers, but the effect was weak compared to that of BMI or age. Contrary to studies of radiographic osteoarthritis our study indicates higher risk of hip than of knee osteoarthritis.