The clinical presentation of thumb hypoplasia is diverse and can be short, thin, or completely absent compared to a normal thumb. Based on its internal anatomy and appearance, it is generally classified into 5 types. The most complex to treat is thumb hypoplasia type 4. Type 4 thumb dysplasia, also known as floating thumb, clinically presents with a lack of a palm or only a palmar bone remaining and a flaccid skin tube attached to the palm of the hand. In the past, this type of thumb dysplasia could only be treated by thumb removal, where the index finger was moved to the thumb position and used as the thumb. Therefore, the treatment of floating thumb is more inclined to preserve the fifth finger, and there are two surgical options for preserving the fifth finger, metatarsal reconstruction and hemimelia reconstruction. Metatarsal reconstruction is the reconstruction of the first metacarpal bone from the foot, which has a certain chance of bone resorption and necrosis. Because the foot needs to bear weight, post-operative care can be troublesome. The child cannot go down to the ground for three months after surgery and can only lie or sit, which is very difficult for active children. The age of metatarsal reconstruction should not be too young, usually the child will miss the stage of establishing the function of the thumb and will be forced to develop the habit of using the index and middle fingers to hold objects, which will have a certain impact on the physical and mental development of the child if he is more introverted. The hemi-metacarpal bone graft reconstruction is a partial reconstruction of the first metacarpal bone from the second metacarpal bone of the affected hand, and the whole surgery is performed only on the hand without any additional trauma to other parts of the hand. The hemi-metacarpal bone graft reconstruction technique can advance the age of surgery to about 6 months to 1 year old, just when the child’s thumb function is established.