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1. Background
Osteoporosis is characterized by the deterioration of bone mass and microarchitecture, leading to impaired bone strength and subsequently fragility fracture [1]. Osteoporotic fractures are defined as low-impact fractures resulting from low-level trauma, such as a fall from a standing height or less that would not ordinarily result in fracture [2,3]. However, osteoporotic fracture is not straightforwardly defined, which sometimes causes misunderstanding. For example, although large studies have shown that nearly all types of fractures occur more often in patients with low bone mineral density (BMD) irrespective of the site [4,5], a low BMD alone might not fully detect the risk of osteoporotic fractures [4] and fractures are not always associated with low BMD [6]. In addition, under such definition, bone fragility does not presumably contribute to fractures associated with a high-level trauma. In a study that compared the BMD of a random sample of women who sustained fractures in either low- or high-level trauma events, the results revealed that, in a high-energy trauma, patients with osteoporosis are more prone to fracture than those without osteoporosis [7]. The exclusion of high-level trauma fractures may result in the underestimation of the contribution of osteoporosis to fractures [7].
The BMD measured at the lumbar spine and hip is currently the standard assessment tool in diagnosing osteoporosis. The relationship between low BMD and major osteoporotic fractures, including the spine [8,9], hip [10,11], humerus [12,13], and forearm [14], has already been established. Considering that advanced age and low body weight are strongly associated with low BMD and increased risk of bony fracture [6,15,16], the World Health Organization (WHO) developed the Osteoporosis Self-Assessment Tool for Asians (OSTA) score calculated using the following formula: (body weight (kg) − age (year)) × 0.2 to identify women at risk for osteoporosis [17]. A significant positive correlation was found between the OSTA index and T-scores of BMD measured by dual energy X-ray absorptiometry at the femoral neck [18,19]. In this developmental study, OSTA performed better than other osteoporotic indices by showing a sensitivity of 91%, specificity of 45%, and receiver operating characteristic curve of 0.79 at the cutoff of −1 [17]. In addition, at the cutoff of −1, the difference in OSTA performance was minimal regardless of using the femoral neck and lumbar...