In the TW3 Bone Age Standards, bone age is categorized into Carpal bone age and RUS bone age, i.e., C bone age and R bone age, which represent the development of the metacarpal and phalangeal bones respectively; R bone age represents the age of the ulnar, radial, and metacarpal phalanges, while C bone age represents the age of the carpal bones. Generally, R-age is used to predict adult height. In children with chronic renal insufficiency and growth hormone deficiency, the carpal bones are more delayed than the metacarpophalangeal bones. In children with congenital adrenal hyperplasia and in children with precocious puberty, metacarpal phalangeal bone age is advanced compared to carpal bone age. In addition, endocrine diseases, genetic diseases, and chromosomal abnormalities can cause changes in the length of the metacarpal phalanges at the wrist, which should be determined and analyzed according to the child’s own condition under the guidance of a medical professional. In conclusion, the R and C bone ages in TW3 are important in determining whether the growth hormone and sex hormone are normal or not, and even have a constructive influence on the diagnosis of some special childhood diseases.