Comparison of the prevalence of radiographic osteoarthritis of the knee and hand between Japan and the United States

OBJECTIVE: There is no direct international comparison of the prevalence of osteoarthritis (OA) between Japanese and Caucasians. We compared the prevalence of radiographic knee and hand OA between women in Hizen-Oshima, Japan, and in Framingham, Massachusetts, USA. METHODS: A population based cross sectional study among 358 women in Japan and 815 women in the USA aged 63 years or older for knee joints, and 157 women in Japan and 655 women in the USA aged 71 years or older for hands. Radiographs were obtained of knees and hands, and were graded according to the Kellgren-Lawrence (K-L) criteria. Definite OA was defined as K-L grade 2 or higher, present in at least one joint of a given group. A person was defined as having OA or not in a given joint group, and we used logistic regression with the US group as referent to determine the prevalence odds ratio of OA among Japanese. RESULTS: The age adjusted prevalence of knee OA in Japanese women was higher than in Caucasians (OR 1.96, 95% CI 1.50-2.56), while the prevalence of hand OA other than distal interphalangeal joint in Japanese was lower than in Caucasians (OR for proximal interphalangeal joint 0.66, 95% CI 0.46-0.93; OR for metacarpophalangeal joint 0.62, 95% CI 0.42-0.90), especially base of thumb OA (OR 0.15, 95% CI 0.11-0.22). CONCLUSION: These findings suggest site-specific differences in the prevalence of OA that may be attributed to genetic and/or environmental factors.