Figure 1.

Targeted areas of the epidemiological study in China. The red circles indicate the locations of surveys of common rheumatic diseases. The yellow circles indicate the locations of hand OA surveys. 1, Heilongjiang; 2, Jilin; 3, Beijing; 4, Shandong; 5, Hebei; 6, Taiyuan; 7, Ningxia; 8, Shanghai; 9, Nanjing; 10, Taiwan; 11, Shantou; 12, Guangzhou; 13, Hong Kong.