I. Risk factors 1. Uncontrollable factors: ethnicity (Caucasians and yellow people have a higher risk of osteoporosis than blacks), old age, female menopause, maternal family history. 2, controllable factors: low body weight, low sex hormones, smoking, excessive alcohol consumption, coffee and carbonated beverages, etc., lack of physical activity, dietary calcium and/or vitamin D deficiency (little light or intake), diseases affecting bone metabolism and the application of drugs affecting bone metabolism (see the section on secondary osteoporosis). II. Clinical manifestations Pain, spinal deformation and the occurrence of fragility fractures are the most typical clinical manifestations of osteoporosis. However, many patients with osteoporosis often do not have obvious conscious symptoms in the early stage, and are often found to have osteoporotic changes only after the fracture occurs by X-ray or bone density examination. Pain: Patients may have low back pain or peripheral pain, and the pain may increase when the load increases or the activity is limited, and in severe cases, there are difficulties in turning, sitting and walking. 2. Spinal deformation: Those with severe osteoporosis may have height shortening and hunchback. Vertebral compression fracture can lead to thoracic deformation, abdominal compression, affecting cardiopulmonary function, etc. 3. Fracture: A fracture occurs after mild trauma or daily activities as a fragility fracture. The common sites where fragility fractures occur are the thoracic and lumbar spine, hip, radius, distal ulna and proximal humerus. Fractures can also occur at other sites. After a fragility fracture, the risk of a second fracture increases significantly. The common clinical indicators used to diagnose osteoporosis are: the occurrence of fragility fracture and/or low bone density, and the lack of clinical means to directly measure bone strength. 1, fragility fracture: is the ultimate manifestation of bone strength decline, there has been a fragility fracture clinically can be diagnosed osteoporosis. Bone mineral density (BMD) is the best quantitative indicator for diagnosing osteoporosis, predicting the risk of osteoporotic fracture, monitoring the natural course of the disease, and evaluating the efficacy of drug interventions. BMD reflects only about 70% of bone strength. The risk of fracture is associated with low BMD, and the risk of fracture is increased when accompanied by other risk factors. (1) Bone density measurement methods: Dual-energy X-ray absorptiometry (DXA) is currently the internationally recognized bone density examination method, and its measured value is used as the gold standard for the diagnosis of osteoporosis. Other bone density examination methods such as various single photon (SPA), single energy X-ray (SXA), quantitative computed tomography (QCT,) etc. can also be used for the reference of osteoporosis diagnosis according to specific conditions. (2) Diagnostic criteria: It is recommended to refer to the diagnostic criteria recommended by the World Health Organization (WHO). Based on DXA measurement: Bone density value less than 1 standard deviation below the peak bone value of healthy adults of the same sex and race is normal; reduction between 1 and 2.5 standard deviations is low bone mass (bone loss); reduction equal to and greater than 2.5 standard deviations is osteoporosis; reduction in bone density in line with the diagnostic criteria for osteoporosis accompanied by one or more fractures is severe osteoporosis. Nowadays, it is also usually expressed by T-Score (T-value), that is, T-value ≥ -1.0 is normal, -2.5 < T-value < -1.0 is bone loss, and T-value ≤ -2.5 is osteoporosis. The bone mineral density of the measured site has the greatest value in predicting the risk of fracture at that site, e.g., the risk of hip fracture is most meaningfully predicted by hip BMD. DXA BMD measurement values are subject to certain deviations due to bone tissue degeneration, injury, soft tissue ectopic calcification and compositional changes, as well as postural differences, and are also affected by the accuracy of the instrument and the degree of operational standardization. Therefore, the application of DXA to determine bone mineral density should be strictly in accordance with quality control requirements (refer to the consensus opinion of the International Society of Clinical Densitometry ISCD). The recommended measurement sites commonly used in clinical practice are lumbar spine 1 to 4 and femoral neck, and the diagnosis should be analyzed in the context of the clinical situation.