• Shigeyuki Muraki, Toru Akune, Hiroyuki Oka, Yuyu Ishimoto, Keiji Nagata, Munehito Yoshida, Fumiaki Tokimura, Kozo Nakamura, Hiroshi Kawaguchi, and Noriko Yoshimura.
• 22nd Century Medical and Research Center and University of Tokyo, Tokyo, Japan. murakis-ort@h.u-tokyo.ac.jp
• Arthritis Rheum. 2012 May 1; 64 (5): 1447-56.

ObjectiveTo examine the incidence and progression of radiographic knee osteoarthritis (OA) and the incidence of knee pain, and their risk factors in Japan, using the large-scale population of the nationwide cohort study ROAD (Research on Osteoarthritis/osteoporosis Against Disability).MethodsSubjects from the ROAD study who had been recruited in 2005-2007 were followed up with knee radiography 3 years later. A total of 2,262 paired radiographs (74.4% of the original sample) were scored using the Kellgren/Lawrence (K/L) grading system, and the incidence and progression rate of knee OA was examined. The incidence rate of knee pain was also examined. In addition, risk factors were tested for their association with incident and progressive radiographic knee OA and incident knee pain.ResultsGiven the ∼3.3-year followup, the rate of incident K/L grade ≥2 radiographic knee OA was 6.9% and 11.9% in men and women, respectively, while that of K/L grade ≥3 knee OA was 8.4% and 13.9% in men and women, respectively. The rate of progressive knee OA was 17.8% and 22.3% in men and women, respectively. The incident rate of knee pain was 21.2% and 27.3% in men and women, respectively. Female sex was a risk factor for incident K/L grade ≥2 knee OA, but was not associated with incident K/L grade ≥3 knee OA or progressive knee OA. Knee pain was a risk factor for incident and progressive knee OA. Previous knee injury was a risk factor for knee pain but not for radiographic knee OA.ConclusionThe present longitudinal study revealed a high incidence of radiographic knee OA in Japan.Copyright © 2012 by the American College of Rheumatology.

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