Prevelence of Osteoarthritis of the Knee is High in Chinese Population Despite Relative Thinness
Osteoarthritis (OA) is a leading cause of disability among older persons in Western societies. Overweight has been identified as an important risk factor for OA of the knee in studies of Western societies, particularly in women. Epidemiologic studies of OA in non-Western populations are scarce. The relative thinness of most Chinese persons would suggest that older persons living in China might have less knee OA than those in the U.S. Zhang et al (Arthritis Rheum 44:2065, 2001) estimated the prevalence of radiographic and symptomatic knee OA in a population-based sample of elderly subjects in Beijing, China and compared it with that reported in the Framingham OA study.
Methods: A sample of persons age > 60 was recruited, using door-to-door enumeration in randomly selected neighborhoods in Beijing. Subjects completed a home interview and a hospital examination including weight-bearing knee radiographs. The protocol was identical to that used in the Framingham OA study. The definitions of radiographic and symptomatic knee OA were also identical to those used in the Framingham study.
Results: Of 2,180 age-eligible Beijing subjects contacted, knee radiographs were obtained in 10787 (82.0%). The prevalence of radiographic knee OA was 42.8% in women and 21.5% in men. Symptomatic knee OA occurred in 15.5% of women and 5.6% of men. Compared with women of the same age in Framingham, women in Beijing had a higher prevalence of radiographic knee OA (prevalence ratio 1.45, 95% confidence interval 1.31-1.60) and of symptomatic knee OA (prevalence ratio 1.43, 95% confidence interval 1.16-1.75). The prevalence of knee OA in Chinese men was similar to that in their white US counterparts (for radiographic OA, prevalence ratio was 0.90; for symptomatic OA, prevalence ratio was 1.02). Interestingly, bilateral (radiographic) knee OA was more prevalent in the Beijing population, while prevalence of severe (radiographic) OA was higher in the US population.
Conclusions: Using identical methods and definitions to evaluate the prevalence of OA in the US white and Chinese populations, a surprisingly high prevalence of knee OA among older Chinese women was found. In contrast, prevalence in men was comparable.
Editorial Comment: In general, the Chinese population is thinner than the US. This was true in this study where the mean weights for Chinese women and men were 61.6 and 69.9 kg, respectively, and mean body mass indices (BMI) were 26.0 and 25.2 kg/m2, respectively. Overweight and female sex have been identified as important risk factors for knee OA in studies of Western populations. The high prevalence of knee OA in Chinese women despite their thinness indicates that other risk factors, other than – or in addition to – overweight, play an important role in the development of knee OA. Both men and women in the Beijing study population reported a high level of physical activity. While this could contribute to the higher prevalence of knee OA in women, it does not account for the equivalent prevalence in the two populations of men. Genetic differences between the two populations may also account for some of the difference in prevalence of disease.
The careful design of this study, in which the Framingham methodology was reproduced and excellent quality control of radiographic readings is maintained, will lend important new information to the study of risk factors for the development of OA. Comparison of the two populations for risk factors for incident disease and for progression of disease will provide important information about etiology of this highly prevalent, disabling and costly disease.