Body mass index associated with onset and progression of osteoarthritis of the knee but not of the hip: the Rotterdam Study.

OBJECTIVE To investigate the relationship between body mass index (BMI) and the incidence and progression of radiological knee as well as of radiological hip osteoarthritis. DESIGN Cohort study. SETTING Population based. PARTICIPANTS 3585 people aged > or =55 years were selected from the Rotterdam Study, on the basis of the availability of radiographs of baseline and follow-up. MAIN OUTCOME MEASURES Incidence of knee or hip osteoarthritis was defined as minimally grade 2 at follow-up and grade 0 or 1 at baseline. The progression of osteoarthritis was defined as a decrease in joint space width. METHODS x Rays of the knee and hip at baseline and follow-up (mean follow-up of 6.6 years) were evaluated. BMI was measured at baseline. RESULTS A high BMI (>27 kg/m(2)) at baseline was associated with incident knee osteoarthritis (odds ratio (OR) 3.3), but not with incident hip osteoarthritis. A high BMI was also associated with progression of knee osteoarthritis (OR 3.2). For the hip, a significant association between progression of osteoarthritis and BMI was not found. CONCLUSION On the basis of these results, we conclude that BMI is associated with the incidence and progression of knee osteoarthritis. Furthermore, it seems that BMI is not associated with the incidence and progression of hip osteoarthritis.