To summarize the overall relative risk of knee osteoarthritis (OA) associated with body mass index, and to estimate the potential risk reduction due to the control of this risk factor.
Six electronic databases were searched up to July 2010. Relative risk was estimated using odds ratio (OR). A random-effects model was used to pool the results. Risk reduction was estimated using population-attributable risk percentage (PAR%), i.e., the proportion of knee OA that would have been avoided if obesity had not been present in the population. The percentage of obesity in different populations was obtained from the International Obesity Task Force.
Forty-seven studies (446,219 subjects) were included in the meta-analysis, of which there were 14 cohort, 19 cross-sectional, and 14 case-control studies. The overall pooled ORs for overweight and obese individuals were 2.02 (95% confidence interval [95% CI] 1.84-2.22) and 3.91 (95% CI 3.32-4.56), respectively. Risk reduction in terms of PAR% for knee OA varied from 8% in China to 50% in the US, depending on the prevalence of overweight and obesity. The reduction was greater in severe symptomatic OA than in asymptomatic radiographic OA.
Obesity is a risk factor for many conditions, including knee OA. The benefit of modifying this risk factor may cause significant risk reduction of knee OA in the general population, especially in Western countries where obesity is prevalent.