(1) What is skeletal age and skeletal age standard? Bone age is the abbreviation of skeletal age, which is a developmental age obtained by comparing the actual development of a child’s bones with the standard developmental level. Bone age represents to a large extent the true developmental level of the child, so it is more accurate to use bone age to determine the maturity of the human body than the actual age. When an individual’s skeletal maturity is compared to a standard chart, and the skeletal maturity corresponds to the standard chart for a certain age, that age is the skeletal age, and it is an indicator for determining bone maturity. (2) Why do doctors often determine the bone age of children? The changes in human bone development are basically similar, and the developmental process of each bone has continuity and stages. Bones at different stages have different morphological characteristics; therefore, bone age assessment can more accurately reflect the level of growth and maturity of an individual. It not only can determine the biological age of children, but also can understand the growth potential of children and the trend of sexual maturity through bone age at an early stage: the adult height of children can also be predicted through bone age, and the determination of bone age is also very helpful for the diagnosis of some pediatric endocrine diseases. It is also a great guide for the treatment of some patients with short stature. (3) Why can bone age reflect the height potential of children? Skeletal age, or bone age for short, is determined by the degree of calcification of a child’s bones. Because bone age can more accurately reflect the developmental level of a person at each age from birth to full maturity, it is most widely used in all developmental ages. In particular, bone age plays a more important role in the analysis and diagnosis of endocrine diseases, developmental disorders, nutritional disorders, hereditary diseases and metabolic diseases. The use of bone age inferred development, thus reflecting the state of physical growth and development, helps to understand the potential of children’s height development. Example: A boy is 12 years old but his bone age is 13 years old, which indicates that although the boy is only 12 years old, he is developing faster and his body has reached the level of physical development of a 13-year-old boy. Since the age of wrist bone maturity for Chinese men is about 18.4 years, the boy would normally continue to grow and develop for no more than 5.4 years. And if his bone age is 11 years, it means that his development is slower and only developed to the level of normal children at the age of 11 years, so under normal circumstances his remaining development time is 7.4 years can be considered that this girl has more potential in height growth. (4) What is the relationship between bone age and age and developmental maturity? The relationship between bone age and actual age can be shown by the bone age difference. This is the difference between actual age and bone age, and also the specific number of years between the two. If the difference between the actual age and the bone age is positive, the bone age is behind the age; if the bone age difference is negative, the bone age is ahead of the age. Usually, ±2 years is the normal range of bone age difference, where a bone age difference of ±1 year is normal. When the rate of increase of bone age is greater than the rate of height growth, the epiphysis will heal earlier and the growth period will be shortened, which will eventually result in the reduction of adult height. (5) When does the bone age of adolescents usually close? Generally, girls are at the age of 16 or 17 and boys are at the age of 18 or 19. Girls grow fastest during puberty at 11-15 years old, and boys grow fastest at 12-16 years old. Puberty is the fastest growing period in a lifetime, and spring is the fastest growing period of the year.