Thumb hypoplasia can be divided into five types. Type I is a slightly abnormal thumb, small and thin, and the interphalangeal muscle is relatively not as good as normal, but the general function is there. Type II is a small metacarpal bone with no interphalangeal muscle, which can be flexed and does not function well on the palm. The pinching, holding, and grasping of the hand are affected, and many movements are difficult to perform, such as clenching when writing. Type III can be divided into type IIIA, type IIIB and type IIIC. These three subtypes are also characterized by poorly developed metacarpal bones, a small, non-functional thumb that can swing at will, and only a relatively wide dermal connection to the palm skin. Type IIIA has a relatively longer metacarpal and type IIIC has a shorter metacarpal length. In type IV thumb dysplasia, also called floating finger, the metacarpal stump is only a little bit smaller and the thumb is smaller and more deformed than in type III. There is no tendon or bone connected to the palm of the hand, only a very small skin tip connected to the palm of the hand. The small skin tip contains blood vessels, which are small but very important and critical. Type V means that there is no thumb at all, only four fingers, and there is a problem with the development of the radial column, as well as most of the angular and sometimes navicular bones. For children with only four fingers, we can only do schematic thumbing. In the case of type IV thumb hypoplasia, we try to preserve the thumb because it has good sensation and blood flow, and we can get some function and a relatively good shape after preserving it.