Wuchuan Osteoarthritis Study is a population-based longitudinal study of natural history of knee osteoarthritis and its risk factors. At baseline and follow-up visits, IPA-Q questionnaire and a radiographs at tibiofemoral (TF) joints will be taken in order to assess the relationship between physical activity and radiographic osteoarthritis worsening.

1025 residents aged ≥ 50 years will be recruited using door-to-door enumeration in randomly selected rural communities in Wuchuan, China, and will be followed in 3 years. At baseline and follow-up visits, subjects will complete a home interview (including, but not limited to, socio-demographic factors, physical activity level using IPA-Q questionnaire,WOMAC questionnaire) and have a weight-bearing posteroanterior semiflexed view of radiographs at tibiofemoral (TF) joints. Radiographic osteoarthritis (ROA) worsening for a knee is defined if its Kellgren and Lawrence (K/L) grade increases by at least 1 grade except for the change from 0 to 1 during follow-up. The relationship between level of physical activity and ROA worsening will be assessed.

Inclusion Criteria:

1. people aged 50 or over
2. Wuchuan permanent resident population

Exclusion Criteria:

1. patients with rheumatoid arthritis
2. the disabled
3. patients with mental disorders
4. laid up for malignant tumor
5. people who live or work outside for more than half a year

People, over 50 years old, in a rural area in Northern China (Wuchuan, Inner Mongolia)