The prevalence of knee osteoarthritis is much higher in Caucasians than in Asians or in black people. Few population-based studies regarding the incidence of knee osteoarthritis were found, with the incidence of knee osteoarthritis being higher in Japanese than in Caucasians. However, strict comparisons among these studies are limited, because the definition of the incidence of knee osteoarthritis is not the same for each study. A few risk factors for knee osteoarthrit is were established, such as female gender and obesity. Several cross-sectional studies have found that the presence of a previous knee injuryis significantly associated with the incidence of knee osteoarthritis, but longitudinal studies did not find this significant correlation. However, the same longitudinal studies found significant associations between previous knee injuries and incident knee pain. One of the limitations in previous studies is the definition of knee osteoarthritis. The most popular grading system for knee osteoarthritis is Kellgren–Lawrence classification. However, joint space narrowing and osteophytosis cannot be separately assessed in this grading system. Recent studies have suggested distinct causes for both joint space narrowing and osteophytosis. These studies have also found an independent association between joint space narrowing and osteophytosis with the quality of life of the person. This is a review of population-based studies for knee osteoarthritis.
To further assess new risk factors or markers, joint space narrowing and osteophytosis should be assessed separately using a fully automatic system that measures joint space width and osteophyte area.