Prevalence and characteristics of unilateral knee osteoarthritis in a community sample of elderly Japanese: do fractures around the knee affect the pathogenesis of unilateral knee osteoarthritis?

Background: The purpose of this study was to investigate the prevalence and characteristics of unilateral knee osteoarthritis (KOA), to investigate what percent of contralateral healthy knees in patients with unilateral KOA progress to KOA, and to investigate whether knee fractures influence unilateral KOA. Methods: Studies were performed every two years from 1997 to 2009 in Miyagawa village, for a total of seven studies. A total of 1239 village inhabitants aged ≥65 years participated in these studies at least once. KOA was defined as a Kellgren-Lawrence (K/L) grade ≥2. Based on the knee X-ray at the first examination, participants were divided into three groups: no KOA (N group), unilateral KOA (U group), and bilateral KOA (B group). The U group was divided into two subgroups: K/L grade II-I combination (II-I group), and the U group without the II-I combination (G>2 group). To investigate whether knee fractures influence unilateral KOA, the fracture history was considered. Results: The percentages of participants classified into the N, B, and U groups (II-I and G>2 group) were 68.4, 21.6, and 10.0 % (7.8 and 2.1 %), respectively. Most of the U group had the II-I combination (78.7 %). The percentages of knee fractures in the N, B, II-I, and G>2 groups were 3.3, 5.3, 6.3, and 38.5 %, respectively. Overall, 49.2 % of the U group proceeded to bilateral KOA over an average of 5.3 years. Conclusions: The prevalences of definite radiographic bilateral and unilateral KOA were 21.6 and 10.0 %, respectively. Overall, 49.2 % of the participants with unilateral KOA developed KOA in the contralateral knee over an average of 5.3 years. If bilateral KOA advanced simultaneously, the II-I group was considered to represent the midpoint of progression to bilateral KOA. Bilateral KOA advanced simultaneously except in cases with a history of knee trauma, such as fractures. [ABSTRACT FROM AUTHOR]