To investigate the incidence of symptomatic keen osteoarthritis(SKOA) and its risk factors among the Chinese elderly population, and to provide references for the formulation of health policies and clinicians' decision-making.

The China Health and Retirement Longitudinal Study(CHARLS) is a nationwide longitudinal survey of persons aged ≥45 years. SKOA was diagnosed when both self-reported knee pain and self-reportedphysician-diagnosis arthritis existed. Relevant variables such as age, gender, regions, education were extracted from the " Demographic Background" and " Health Status and Functioning" databases of CHARLS in 2011, 2013, 2015 and 2018, and combined into a longitudinal study database according to the respondent ID. The constituent ratio of covariates, the cumulative incidence of SKOA and 95% confidence interval (CI) of the respondents in each survey year were calculated. Finally, Cox proportional hazards model was used to identify the risk factors of SKOA.

In 2011 to 2013, 2013 to 2015, and 2015 to 2018, the cumulative incidence of SKOA among middle-aged and elder Chinese adults were 7.09% (6.27-8.01) %, 13.13% (12.10-14.24) %, and 23.10% (22.45-23.79)%, respectively. It was on a marked upward trend. The incidence was higher among females than males, increases with age. Female[hazard ratio (HR)=1.67, χ²=9.98, P<0.001], increasing age(50-60 years HR=1.60, χ²=7.67, P<0.001, 60-70 years HR=1.96, χ²=10.76, P<0.001, age ≥70 years HR=2.16, χ²=9.94, P<0.001), and rural area(HR=1.24, χ²=4.74, P<0.001) were associated with a higher risk of incident SKOA. Education level(junior and high school and vocational education HR=0.68, χ²=-4.57, P<0.001; above college HR=0.59, χ²=-2.55, P=0.01) and physical activities(HR=0.32, χ²=-7.08, P<0.001) were associated with a lower risk of incident SKOA.

The cumulative incidence of SKOA in middle-aged and elderly population in China is relatively high and is on the rise. Low education and lack of physical activities are confirmed to be risk factors of incident SKOA.