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?

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.