A hypoplastic thumb is a thumb that is missing any anatomical structure to varying degrees, it will be smaller in appearance than a normal thumb, most notably a small nail, thin thumb and an abnormally shaped joint. The line of force of a normal thumb is usually straight, which is not the case in a dysplastic thumb; it will be laterally deviated, and the distal end of the thumb may be deviated to the radial side, and there are problems with the piriformis muscle.Blauth classifies thumb dysplasia into five types, and except for dysplasia I, in which there is little difference in the look of the atrophied piriformis muscle, in dysplastic thumbs of type II and above the piriformis muscle is also varied, and the palm does not have such a nice contour; it is deflated and flat. and flat. The thumb does not have a curvature when viewed from the side, and is either straight down or concave, which are obvious differences in the appearance of thumb hypoplasia. In addition to cosmetic changes, thumb dysplasia is also reflected in function. In type I dysplastic thumb, the overall difference is not very obvious, the basic function is there, it can be bent, can be extended, can be opposite to the palm, and can be retracted or abducted, but its strength is definitely on the low side. This kind of children can not intervene, do not need to do surgery, usually do the functional exercise can be. Type II thumb dysplasia has no curvature at the interosseous muscle, you can directly feel a very hard bone, the thumb can move, but only the power of the flexor muscle is working, the metacarpal bone can’t move, and some fine movements will be more difficult to do, more tired. In type III thumb dysplasia, the connection between the thumb and the palm of the hand is less and less, and the metacarpal bone on the x-ray is also smaller. In type IV thumb dysplasia, which is often referred to as floating thumb, the metacarpal bone is completely missing or only the metacarpal bone remains, and the appearance of the thumb and the palm of the hand is only connected by a loose skin tube, and the thumb is completely dysfunctional, and it can only swing with the swing of the hand. Among the 5 types of thumb dysplasia, type IV thumb dysplasia is the most difficult to operate, especially the finger preservation surgery of floating thumb, like in the past, it will be treated by metatarsal reconstruction surgery, which takes the bone from the foot and reconstructs the first metacarpal bone, and it can have a better shape and function after the operation. Considering that metatarsal reconstruction will affect the weight bearing of the foot, we are now using hemi-metacarpal bone grafting technique to reconstruct the first metacarpal from the second metacarpal bone. The surgery is performed on the hand only, and it will not affect other parts of the child’s body, so that the thumb’s shape and function can reach a more desirable state after the surgery. The most serious is the Ⅴ type of thumb dysplasia, manifested in the complete absence of the thumb, can see only four fingers, this situation can be done to show the finger bunionization surgery, although the reconstruction can not be a new thumb, but also have the function of the thumb. In other words, as long as the thumb is not completely absent, even if it is a floating thumb, as long as parents don’t give up, there is still hope that the surgery can preserve the five fingers and give them a more desirable shape and function.