Keywords: osteoarthritis • osteoarthritis of the knee • osteoarthritis of the spine • southeast Asia • urbanization Osteoarthritis Osteoarthritis (OA) is a multifactorial and complex disease that involves change in articular bone and cartilage structure. The multifactorial nature of OA is that the disease is not a single entity, but encompasses many entities, including the the loss of cartilage within synovial joints, hypertrophy of bone, and thickening of the capsule. The complexity is in the causality and etiology of the disease as its risk is determined by multiple, and probably interactive, effects of genetic and environmental factors. A reasonable definition that can capture the complexity and multifactorial nature of the disease is "a heterogeneous group of conditions that lead to joint symptoms and signs, which are associated with defective integrity of of cartilage, in addition to related changes in the underlying bone at the joint margins" [1]. Although OA can affect any joint in the body, it is often found at the hands, knees, hips, and spine.A challenge in studies of OA is in the diagnosis. There is a considerable disparity between clinical and radiologic diagnoses. There are many radiologic methods for diagnosing OA, but the Empire Rheumatism Council system of grading first described by Kellgren and Lawrence [2] is probably the most widely used scale in epidemiologic studies. The Kellgren-Lawrence method is actually a system of OA grading based on the presence or absence of osteophytes, joint space narrowing, subchondral sclerosis, and bony cysts. In an epidemiologic study, it was noted that while the prevalence of clinically diagnosed knee OA was approximately 18%, the radiologically based method identified 25-30% [3]. The degree of diagnostic agreement of between clinical diagnosis and radiologic diagnosis was moderate [3], which was confirmed by a recent meta-analysis [4].However, with recent advances in imaging technology (e.g., MRI), there has been a shift in thinking about OA. Instead of being viewed as a 'tear and wear' disease, OA is now viewed as an active disease with disruption in processes involved in the maintenance of healthy cartilage [5]. Nevertheless, image-based diagnosis of OA has not been widely used in research studies [5].Prevalence of OA OA is the most common musculoskeletal disorder among the elderly, and women are more likely to be affected than men. A population-based analysis based on NHES survey data found that the prevalence of hand OA was 29.5% among those aged 25 years and older [6]. A recent analysis of NHANES III data found that approximately 35% of women and men aged 60 years and above had radiographic OA of the knee [7]. In a Chinese population aged ≥60 years, the prevalence of knee OA was 22% in men and 43% in women, and this prevalence was 45% higher than that in the US white population [8]. In a Japanese rural population, the prevalence of knee OA was 30% in women and 11% in men.Surprisingly, the prevalence of spinal OA has not been well documented. Based on a f...