Factors associated with radiographic osteoarthritis of the knee among community-dwelling Japanese women: the Hizen-Oshima Study.

Background: Osteoarthritis (OA) of the knee is the most common form of arthritis and is a major contributor to functional impairment and reduced independence in older adults. In Japan, knee OA is a frequent cause of pain and disability, but few epidemiological studies have examined the demographic or lifestyle factors that influence OA of the knee. We examine the risk factors for OA of the knee among Japanese community-dwelling women aged 40-89 years (mean age 64.2, SD 9.6 years).

Methods: Anteroposterior weight-bearing knee radiographs were graded according to the criteria described by Kellgren-Lawrence (K/L). We defined knee OA as a K/L grade of 2 or higher (using a 0-4 scale) based on the plain radiographs. History of knee injury, type of occupation, and daily intake of antioxidant nutrients including vitamin C and carotene were obtained from questionnaires.

Results: Among the 582 subjects, 195 women (33.5%) suffered from knee OA. Logistic regression analysis showed that older age [odds ratio (OR) 1.8, 95% confidence interval (95% CI) 1.6-2.1 per 5-year increase], higher body mass index (OR 2.2, 95% CI 1.7-3.0 per 5-unit increase) and previous knee injury (OR 3.1, 95% CI 1.7-5.6) were associated with knee OA. The occupation of farming and intake of antioxidant nutrients were not associated with knee OA.

Conclusion: Older age, obesity and previous knee injury represent independent risk factors for knee OA among Japanese women.