English

Abstract

Introduction 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 crosssectional 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. Conclusion 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. Introduction Knee osteoarthritis (OA) is a major public health issue and causes chronic pain and disability among elderly in most of the developed countries. It is characterised by several pathological features, including joint space narrowing and osteophytosis. Despite the urgent need of strategies for the prevention and treatment of this condition, demographics on the overall disease prevalence and the affected subgroups are not adequately characterised yet. The reported prevalence of radiographic knee OA differs considerably among previous population-based epidemiologic studies.In addition, apart from age, sex, obesity and occupational activities, there are only a few other established risk factors for knee OA. We aimed to review the literature on population-based studies investigating knee OA. Prevalence of knee osteoarthritis Twelve previously published studies on the prevalence of knee OA were identified after performing a search in the English literature1–12 (Table 1). Epidemiologic studies on elderly Caucasians in the United States and Europe have shown that the prevalence of knee OA with Kellgren– Lawrence(KL) grade 2 or higher was 30–40%; where as studies in Asia have found a prevalence of 60% or higher. Thus, the prevalence of knee OA is higher in Asian populations than in Caucasian populations. Based on these studies, Caucasians show a lower prevalence of radiographic OA than that found in other races. Furthermore, the Johnston County study and the National Health and Nutrition Examination Survey (NHANES) studies reported that African-Americans have a higher prevalence of radiographic knee OA than did Caucasians. However, in the NHANES studies, the prevalence rates of knee OA were lower than those in other studies;this discrepancy was explained by differences in radiographic acquisition. In these studies, knee radiographs were obtained in a non-weight-bearing position, as opposed to other studies, where in knee radiographs were obtained in a weight-bearing position. The Chingford study presented lower prevalence of knee OA because subjects were much younger than those who participated in other studies. In terms of KL grading, KL grade 2 indicates the presence of osteophyte formation; and grade 3 indicates joint space narrowing in addition to osteophyte formation; KL ≥ 2 is generally thought to be the standard for the diagnostic criterion of knee OA13. However, accumulating evidence has shown that osteophytosis and joint space narrowing have distinct aetiologic mechanisms, and their progression is neither constant nor proportional14. Hence, to assess these two pathological features separately, the * Corresponding author Email: murakis-ort@h.u-tokyo.ac.jp 1 Department of Clinical Motor System Medicine, 22nd Century Medical and Research Center, Faculty of Medicine, University of Tokyo,7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8655, Japan 2 Department of Orthopaedic Surgery, Faculty of Medicine, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8655, Japan 3 Department of Joint Disease Research, 22nd Century Medical & Research Center, Faculty of Medicine, University of Tokyo,7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8655, Japan