The risk of osteoporosis (OP) is a pathophysiological phenomenon that occurs with age. Osteoporosis (OP) is a pathophysiological phenomenon that occurs with age, and is one of the most important factors causing an increased risk of fracture. The concept of “osteoporosis” was first proposed by Pommer, a European pathologist, in 1885, and the concept of osteoporosis was explicitly proposed by Albright in 1941. It is a systemic bone disease characterized by a decrease in bone mass, thinning, fracture and reduced number of bone trabeculae, porous and thinning bone cortex, which leads to an increase in bone fragility and fracture risk. It is characterized by an equal decrease in bone mineral and bone matrix. Bone strength is mainly dependent on two factors: bone mineral density and bone mass, and the reduction in bone strength makes bone susceptible to fracture when subjected to external forces. 2. Epidemiology In the 1990s, about 200 million people worldwide were threatened by osteoporosis, and 75 million people suffered from osteoporosis. In the United States, the prevalence of osteoporosis in men and women over 50 years of age is 3% to 6% and 13% to 18%; the prevalence of low bone mass in men and women is 28% to 47% and 37% to 50%. In a Canadian study of osteoporosis, the prevalence of osteoporosis of the lumbar spine and osteoporosis of the femoral neck in women was 12.1% and 7.9%, respectively, with an overall prevalence of 15.8%; in men, the prevalence of osteoporosis of the lumbar spine and osteoporosis of the femoral neck was 2.9% and 4.8%, respectively, with an overall prevalence of 6.6%. The serious consequence of osteoporosis is fracture, with fractures of the lumbar spine, hip and wrist bones being the most common. The total prevalence of fracture in people over 50 years old is 26.6%, hip fracture is 1.9%, forearm fracture is 4%, and vertebral fracture is 13.1%. 3, etiology 3.1, endocrine factors Hormones related to the occurrence of osteoporosis include sex hormones (estrogen, androgen and progesterone), parathyroid hormone, calcitonin, active vitamin D, thyroxine, corticosteroid hormone and growth hormone, etc. The first four hormones, especially sex hormones, play a decisive role in the occurrence of osteoporosis, especially the impact on women is more significant. Estrogen inhibits bone resorption, enhances osteoblast activity, inhibits osteocalcinolysis and promotes bone reconstruction, etc. It can act directly on the kidney to increase 1A-hydroxylase activity and promote 1,25-dihydroxyvitamin D3 production and calcium absorption; it can promote calcitonin secretion and increase its serum basal value; it acts on the parathyroid gland to reduce parathyroid hormone secretion and inhibit bone resorption; it acts on osteoblasts and osteoclasts to prevent bone resorption. It acts on osteoblasts and osteoclasts to prevent bone resorption. Androgens have a role in promoting protein synthesis and bone matrix synthesis. The elderly are more prone to osteoporosis because of the decrease in estrogen and androgen production due to hypogonadism. 3.2, nutritional factors In the dynamic balance of bone resorption and bone formation, two elements, calcium and phosphorus, have a greater impact on bone, and abnormal calcium and phosphorus metabolism is the main cause of osteoporosis. In addition, abnormalities in protein, trace elements (fluorine, magnesium, zinc), vitamin C and vitamin D are also closely related to osteoporosis. (1) Calcium: The amount of calcium in adults is about 1.5% of body weight, of which more than 95% is stored in the bones to form the “calcium and phosphorus pool”, which is the main raw material for bone mass. Calcium deficiency is one of the major causes of osteoporosis, with a minimum daily calcium requirement of 600-1000 mg for a normal adult of about 10 mg of bone calcium loss per day. (2) Phosphorus: Phosphorus is the second most important inorganic component of bone after calcium. 80% of phosphorus exists as hydroxyapatite in bones and teeth, while the other 20% exists as organic phosphorus in soft tissues and body fluids. Phosphorus and calcium together in bone metabolism, low phosphorus can promote bone resorption, reduce the rate of bone mineralization; high phosphorus to reduce intracellular calcium concentration, promote the secretion of parathyroid hormone, increased bone resorption, leading to osteoporosis. (3) magnesium: magnesium is not only the key substance to promote calcium absorption, but also can promote the hydroxylation process of vitamin D, regulate the balance of parathyroid hormone and calcitonin. When magnesium deficiency, the release of parathyroid hormone, calcitonin is inhibited and affect the absorption of calcium in bone. (4) protein: protein is an important raw material for the synthesis of bone organic matter, insufficient or excessive intake will play a negative role in regulating calcium balance and bone mass. It is well established that intestinal calcium absorption is inversely proportional to protein intake, especially acidic amino acids can inhibit intestinal calcium absorption, and excessive sulfur-containing amino acids can acidify urine, reduce calcium reabsorption by renal tubules, and promote urinary calcium excretion. Excessive protein intake can affect the body’s environment, interfere with the balance of calcium and phosphorus metabolism, and cause excessive calcium loss; while the negative nitrogen balance caused by insufficient intake can cause insulin growth factor (IGF-I) deficiency, which prevents osteoblasts from building essential organic matrix, prevents bone mineral deposition, reduces bone formation and affects bone quality. Normal adult daily protein requirement is about 70 g. When protein intake increases by a factor of 1, urinary calcium excretion increases by 50%. (5) Other: Inadequate intake of vitamins, excessive alcohol consumption, smoking, high salt and high caffeine diets, etc. are likely to lead to reduced bone formation and increased bone resorption, thus causing osteoporosis. 3.3, gender and age factors Age is one of the main factors affecting the human bone mineral content. 30-40 years old when the bone volume reaches its lifetime peak, and maintain a relatively stable 5-10 years. Bone mass starts to decrease slowly at the age of 40-49 years for women and 40-64 years for men. In the 5-10 years after the age of 50, especially after menopause, bone loss is dramatic due to the decline in blood estrogen levels, with a peak loss above the age of 80, and the prevalence of osteoporosis in women is up to 100%. 60-year-old women have a 1-fold increase in the incidence of fracture for every 5 years of age, and 80-year-old Asian women have a 1% annual risk of hip fracture. In contrast, bone loss in men is always slow, and the total amount of bone loss is less than in women, so the incidence of osteoporotic fractures is also lower than in women. 3.4. Disease and drug factors Some systemic diseases, such as hyperparathyroidism, hyperthyroidism, diabetes, liver and kidney diseases, gastrointestinal diseases, immune diseases, etc., can cause osteoporosis. Long-term use of certain drugs (adrenal glucocorticoids, anti-epileptic drugs, contraceptives, anti-tuberculosis drugs, aluminum-containing antacids and heparin, etc.) can also affect the absorption of calcium, increasing urinary calcium excretion and accelerating bone loss, thus leading to osteoporosis. 3.5, genetic and immune factors related to the family survey found that 46% ~ 62% of bone density is determined by genetic factors. Therefore, genetic factors are also an important reason for the occurrence of osteoporosis. Immune function has a regulatory role in bone reconstruction, and its functional changes have a certain relationship with osteoporosis. 3.6, disuse and environmental factors Older people have reduced mobility, outdoor exercise and sunlight, and reduced vitamin D synthesis, resulting in decreased intestinal calcium and phosphorus absorption and reduced bone formation and mineralization. Patients who need long-term external fixation due to fracture or bone disease or those who are bedridden and paralyzed for a long time are prone to osteoporosis. Environmental pollutants contain heavy metals such as lead, aluminum and cadmium, which are harmful to bones, and can affect the absorption of calcium and phosphorus in bones after entering the body through breathing or diet. 4, classification 4.1, primary osteoporosis primary osteoporosis is mainly caused by age, organ physiological function degeneration and reduced secretion of sex hormones, and is divided into type I and type II osteoporosis. (1) Type I: Postmenopausal osteoporosis is usually referred to as type Ia, and male osteoporosis is referred to as type Ib. Type Ia osteoporosis occurs in women 5-15 years after menopause, and the pathogenesis is mainly caused by a significant decrease in estrogen secretion and mediated by osteoclasts, resulting in a high-conversion osteoporosis in which bone resorption is greater than bone formation. Laboratory tests show that most biochemical markers of bone resorption and bone formation are higher than normal, characterized by decreased intestinal calcium absorption and increased bone loss, with the most significant loss of trabeculae, mostly in the mid-axis bones (spine) and gradually spreading to the peripheral bones (distal radius, upper femur, lower tibiofibula), with fractures mainly in the thoracic and lumbar spine and distal radius. Type Ib osteoporosis is caused by a decrease in androgen (testosterone) levels and activity, and is a common cause of osteoporosis in men. Androgen levels decrease with age, with nearly half of men older than 50 years having lower than normal serum testosterone levels, even by 50%, and the degree of decline in testosterone levels correlates significantly with increased bone loss. When the androgen level decreases to a certain level, the balance between bone resorption and bone formation is lost, which shows a decrease in bone formation and an increase in bone resorption, thus causing osteoporosis. The fractures mostly occur in the hip, mainly in the femoral neck and intertrochanteric fractures. (2) Type II: It is more common in people over 70 years old, with a male to female ratio of 1:2. This type of osteoporosis occurs due to a decrease in vitamin D receptor reserve and impairment of intestinal calcium absorption, resulting in a decrease in blood calcium levels and accelerated bone loss; reduced exercise, insufficient sunlight, reduced gastrointestinal digestive function, and inadequate intake of nutrients and trace elements also affect osteoblast activity, resulting in reduced bone formation. The bone loss mainly occurs in the trabeculae, but also in the bone cortex. 4.2, secondary osteoporosis due to a disease or drugs and other causative factors triggered by osteoporosis, according to the cause can be summarized as follows: (1) endocrine osteoporosis. This includes diabetic osteoporosis, hyperthyroidism osteoporosis, hyperparathyroidism osteoporosis, etc. (2) Drug-related osteoporosis. Including adrenocortical hormone osteoporosis, osteoporosis affecting liver enzymes, etc. (3) Chronic obstructive pulmonary disease (COPD) causes osteoporosis. In middle-aged and older adults with COPD, smoking, hormone therapy for COPD, inadequate vitamin D intake, reduced sexual function, decreased body mass index, and reduced outdoor and indoor activity are all factors that can trigger or exacerbate COPD osteoporosis. (4) Disuse osteoporosis. It is more pronounced in the limb bones and hip bones, and less in the medial bones. Osteoporosis is prone to fracture, and fracture can be followed by osteoporosis, thus forming a vicious circle. 4.3. Idiopathic osteoporosis refers to unexplained osteoporosis in children, adolescents and adults. It includes osteoporosis in adolescents, osteoporosis in young adults, and osteoporosis during pregnancy and lactation. This type of osteoporosis is uncommon and the etiology and pathogenesis are unknown. The main clinical manifestations are unexplained back, low back and hip, foot pain and fractures, and radiographs mostly show bone resorption in the corresponding areas.