The first metacarpal bone of the baby’s thumb is underdeveloped and in a state of suspension, looking like a meatball of weakness. This is a type IV thumb hypoplasia, called floating thumb. Many parents have misconceptions about their baby’s floating thumb, thinking it is a ball of meat without any feeling. But in fact, the floating thumb has sensation, can sense hot and cold, sense pain, and grows. Although it is not supported by the metacarpal bone like a normal thumb, it has nerves and blood vessels. In the face of such a thumb, it is a great pity to remove it directly to make the thumb of the demonstrator, and we recommend to keep it. There are two main methods to preserve the floating thumb: metatarsal reconstruction and hemi-metacarpal bone graft reconstruction, and I personally prefer the latter. The floating thumb lacks a metacarpal bone, so we cannot create a bone out of thin air to reconstruct it, we can only take bone from other parts of the body to reconstruct it. The metatarsal bone reconstruction is obtained from the bone of the foot, and the baby cannot bear weight for three months after the operation, and the care is more tedious. After healing, the foot will not only leave obvious scars that affect the beauty, but also cause permanent damage, and the baby will never be able to run or jump vigorously again. Half metacarpal bone graft reconstruction is to take part of the bone from the second metacarpal bone to reconstruct the first metacarpal bone, the whole operation is only carried out on the hand, there is no problem that affects the foot, and post-operative care is relatively simple. The most important thing is that the baby’s surgery is brought forward to around 6 months to 1 year old, just when the baby is establishing the function of the thumb, so that the baby will not be forced to form the habit of using the middle finger of the index finger to hold objects because the thumb cannot be used.