Low prevalence of knee and back pain in southeast China; the Shantou COPCORD study.

OBJECTIVE To determine whether the previously noted low prevalence of knee pain (KP) and lumbar pain (LP) in rural southern China compared with the high prevalence observed in North China was also true in a southern urban population. METHODS A population based sample of 2040 adults > or = 16 years of age was studied in Chenghai City, close to the rural area previously studied on the southeast coast of China. Primary healthcare workers administered the COPCORD Phase I and II questionnaires. Those with rheumatic symptoms were recalled for medical examination, with a response rate at examination (phase III) of 98.4%. Those suspected of having arthritis had radiographs and laboratory tests. Prevalences were age and sex adjusted to the total of populations previously reported. RESULTS (1) The prevalence for all rheumatic symptoms at phase III was 18.1%. Of the 7.5% with KP, 55% had osteoarthritic changes on radiograph (KOA) compared with 29% of a sample with no KP (p < 0.001). Of the 11.5% with LP, 69% had degenerative changes on lumbar spine radiograph (LOA). (2) Of residents in single-level houses the prevalence was 5.6% for KP and 7.9% for LP, whereas in 4 to 6-level apartment buildings these rates were significantly higher, 9.1% and 16.2%, respectively. All these pain rates were significantly lower than noted in rural North China. The prevalence of pain together with radiographic OA changes in the knee (KOA) was half the rate in single-floor residents (2.7%) compared to apartment residents (5.3%), as was lumbar spine degenerative disease (5.3% vs 11.5%). CONCLUSION The prevalence of knee and lumbar spine pain in this southern urban sample was confirmed to be much lower than in the rural sample in the North, although higher than in the rural sample in the South. Comparing COPCORD studies of Han Chinese in Shanghai and Malaysia there was a decrease in prevalence of knee and back pain with latitude, suggesting an association with climate. Knee and back pain and radiological degenerative changes in the knee and lumbar spine were twice as prevalent in apartment residents than in those living in older single-level houses. Further study is needed to explain these observations.