Change in body mass index during middle age affects risk of total knee arthoplasty due to osteoarthritis: a 19-year prospective study of 1003 women.

The evidence linking body mass index (BMI) to severe OA shows a strong association in the knee. There are limited data exploring the effect of BMI on the risk of joint arthroplasty in a healthy population with long periods of follow up. We compared the self-reported BMI at age 20, measured BMI at baseline, year 5 and year 10 with the year 19 risk of total knee arthroplasty (TKA) in a well-described, population based cohort of healthy women. A total of 733 women attended the 19th year visit, of whom 31 underwent TKA and 676 were used as a control group after 26 were removed for having hip arthoplasty. Using logistic regression, an increase in 1 unit of BMI at baseline was associated with a 10.5% increased risk of TKA (p=0.017) and at year 5 the increased risk is 8.6% (p=0.042). When adjusted for baseline age and smoking, baseline BMI was the only significant predictor of TKA at 10.0% with p=0.024. There was no significant association at 10 years or for change in BMI over time. In this prospective, population based study, BMI predicted the risk of TKA for OA. The risk was greatest at baseline when the patients were in middle age suggesting that this is the most important time to target weight reduction interventions.