1.What is bone age: Human growth and development can be expressed in two “ages”, namely, life age (calendar age) and biological age (bone age). Bone age is short for skeletal age and is determined with the help of a specific image of the bone in the X-ray camera. In order to find out the age of a person’s bones, an X-ray of the wrist of the left hand is usually taken, through which the doctor observes the degree of development of the metacarpal phalanges, wrist bones and the ossification centers of the lower radius and ulna of the left hand to determine the age of the bones. It is a biological age that reflects the degree of physical development by measuring the changes in size, form, structure and interrelationship of bones, and expresses it in the form of age in years through statistical processing. 2, standard bone age film shooting method: standard bone age film, only need to take a left hand orthopantomograph. When taking the film, the five fingers of the left hand are opened naturally, the palm is down, the middle finger and forearm are kept in a straight line (try not to deviate from the left and right, and the arm is flattened and not lifted up), the X-ray bulb is aligned with the third metacarpal bone, and the distance between the bulb and the X-ray film is about 80CM. 3, factors affecting bone development: many diseases affect bone development, making it into advance or backward, such as adrenal cortical hyperplasia or tumor, precocious puberty, hyperthyroidism, simple obesity with excessive figure growth, ovarian granulosa cell tumor, etc. will lead to early bone age; while ovarian hypoplasia (Turner syndrome), chondrodysplasia, pituitary dwarf (growth hormone deficiency), low A, etc. will lead to significant lag in bone age. The most important factor is the hypothalamic-pituitary-gonadal axis system. Hormones secreted by endocrine glands such as growth hormone, thyroid and adrenocorticotropic hormone also play a regulatory and controlling role in skeletal development, among which sex hormones play a leading role in skeletal development during puberty. 4.Bone age assessment clinical significance The changes of human bone development are basically similar, and the development process of each bone has continuity and stages. Bones at different stages have different morphological characteristics, therefore, the aspects of growth and development that often require the use of bone age assessment are: (1) bone age assessment can more accurately reflect the level of growth and maturity of an individual; (2) it can not only determine the biological age of a child, but also provide an early understanding of the growth potential of a child and the trend of sexual maturity through bone age; (3) bone age can also be used to (3) Bone age can also predict the adult height of children, which can be used for the selection of sports talents, artistic talents and other special talents with different height requirements; (4) The determination of bone age is also very helpful for the diagnosis of some pediatric endocrine diseases; (5) To guide the clinical use of endocrine drugs. The difference of biological age (bone age) – life age within ±1 year is called normal development. The difference between biological age (bone age)-life age > 1 year is called early development. If the difference between biological age (bone age) and life age is <1 year, it is called developmental delay. Bone age determination plays an important role in the x-ray diagnosis of certain endocrine diseases, metabolic disorders and growth disorders. Abnormalities in bone age are often an aspect of the presentation of certain endocrine disorders in pediatrics. According to the latest TW3 assessment method, when the bone age reaches 16.5 years for boys and 15.0 years for girls, the epiphysis is complete, the skeleton reaches adulthood, and the height no longer grows. However, the age at which the epiphysis is completely closed is different for different bone age assessment methods. For example, for the TW2 method released in 1975, the epiphysis is completely closed at 18.3 years old for boys to reach adulthood, a difference of 1.8 years from TW3, and the epiphysis is completely closed at 17.2 years old for girls to reach adulthood, a difference of 2.2 years from TW3.