<正>Objective:To explore the prevalence rate of knee joint osteoarthritis and its pathogenetic fea- tures among the middle-aged and old aged people in the urban and rural area of Xi’an.Methods:From May to October 2005

1538 Han nationality above 40 years in Xi’an were investigated according to strati- fied and cluster random sampling.The same questionnaire was delivered to subjects who had been given normotopia and lateral position radiographic examination in both knees.Excluded from etiological arthri- tis

some subjects with clinical symptoms and a radiographic grade （beyond Kellgren & Lawrence gradeⅡ） were finally diagnosed as spontaneous knee joint osteoarthritis.All analyses were performed with SPSS 13.0 and t test

U test.Single factor analysis and multiple logistic regression analysis were used to analyze dates.Results:The total prevalence of spontaneous knee joint osteoarthritis was 12.1% with 2.5% and 2.1% for right and left knees

respectively.The prevalence of knee joint osteoarthritis in wom- en was 2.5 times of that in men （17.2% vs 6.8%

P=0.000）.the osteophyte prevalence in women was 2.3 times of that in men （26.5% vs 11.4%

P=0.000）.The prevalence of knee joint osteoarthritis and osteophyte increased with the growth of age.So did the symptomatic knee

except for the age group of 56- 60 years and 66-70 years.The prevalence of symptomatic knee joint for urban area was significantly higher than that for rural area （56.3% vs 45.3%

P=0.003）.In women

the prevalence of knee joint os- teoarthritis increased significantly with the increasing of body mass index

which had not been observed in men.Female and obesity are the risk factors for osteoarthritis

but bean and its products and meat could prevent the osteoarthritis.Conclusion:Old age

female and obesity serve as risk factors for knee joint os- teoarthritis.