Bone age: Clinically, the bone age is defined as the age at which the skeletal maturity of each ossification center corresponds to a certain age based on the time of appearance, size, morphology, density, etc. of the ossification centers in comparison with the standard atlas. It is an indicator for determining bone maturity. With the growth of age, the ossification center of the epiphysis of the long bone appears regularly in a certain order and location, which can reflect the maturity of the growth and development of the long bone. To determine bone age, X-ray film is mainly used, generally the best X-ray film of the left hand, to understand the development of the carpal, metacarpal and phalanges. 10 years old carpal ossification centers appeared in full, with a total of 10, so the number of carpal ossification centers in the age of 1-9 years old is about the number of years of age plus 1. To further determine the age of the bone and distinguish the disease. To determine the degree of calcification of the bone, three things are important: 1) the number and size of the ossification centers; 2) the morphology of the ossification centers and epiphyses; and 3) the healing of the epiphyses and diaphyses. The age of a person can be determined by comparing it to the bone age standard used as a normal value. The use of bone age to infer development reflects the state of growth and development of the body and helps to understand the potential for height development in children.