There are two types of thumb dysplasia, type 5 and type 4. type 5 thumb dysplasia is a complete loss of the thumb, which can only be treated with thumb thumbing, where the index finger is moved into the position of the thumb and used as a thumb. In contrast, type 4 thumb dysplasia is a bit better. Although there may be no metacarpal bone, there is a small ball of flesh on the radial side of the index finger, which is the child’s thumb, because it can not use its strength, and can only swing with the swing of the hand, so it is called the floating thumb, which can be reconstructed, so that the child’s five fingers can be preserved. In this case, the thumb can be reconstructed so that the child’s five fingers can be preserved. For the reconstruction of the floating thumb, I mainly use the hemimetacarpal bone grafting reconstruction technique, and the earliest time that the child can receive the surgery is around 6 months to 1 year of age. The whole surgery is divided into two phases, and the form and function can be built up step by step.