Hospital for Special Surgery treats many types of congenital hand differences that affect the fingers, including syndactyly and polydactyly.
Polydactyly means “many fingers (or toes)” in Greek, and it is one of the most common congenital limb differences in newborn children. Children with polydactyly are born with one or more extra fingers or toes. These additional fingers or toes can be small nubbins, fully formed extra digits, or anything in between. The extra digit can be next to the thumb/big toe or the pinky/pinky toe or in the middle of the hand or foot. Sometimes, particularly when the extra digit is in the middle, the fingers or toes do not completely separate from each other: This is called synpolydactyly.
At about four weeks of gestation, the growing human embryo develops four limb buds that will eventually become the arms and legs. At about six weeks, the hands and feet begin to form in the shape of a paddle at the end of the limb buds, which by this point look like little arms and legs. The paddle then develops four clefts, separating the hand paddle into four fingers and one thumb in the hands, or five toes in the feet.
Occasionally, either because of a random occurrence or because it was genetically inherited, a fifth cleft will develop, creating another finger or thumb, or a sixth toe.
The three basic types are based on the location of the extra cleft that occurs during fetal development: The extra cleft can be in the middle of the big toe or thumb (“preaxial”), in the middle of the hand (“axial” or “central”), or over the pinky finger or toe (“postaxial”).
If the cleft is on the thumb side of the hand, the material that was to become the thumb will be split into two thumbs. Usually, the more central one is larger and better formed, but occasionally the split will be down the middle and both thumbs will be similar in size and shape. However, both will be smaller than a typical thumb. How early that fifth cleft develops influences how deep the cleft goes. Some thumbs are split at just the bones on the end, whereas others are split all the way down to the base.
The same is true for an extra digit at the pinky side of the hand. The extra pinky or pinky toe on the outside is usually smaller. Large, extra, postaxial digits are typically associated with genetic disorders such as Ellis-Van Creveld Syndrome. Small nubbins on the pinky side of the hands and feet are also often genetic and common in children with African ancestry.
There are also polydactyly cases known as “mirror hand” or “mirror foot,” in which an entire hand or foot is duplicated, creating numerous extra digits.
Polydactyly is one of the most common congenital limb differences in newborn infants, occurring in about two out of every 1000 live births.1
Diagnosis is obvious in the more severe types but, in the thumb, it is sometimes missed if the split just affects the last bone. X-rays are not useful in children younger than one year since, most of the bones have not mineralized yet and are therefore not visible on X-ray. Generally, X-rays are performed only for surgical planning and are done between 18 and 24 months of age. MRI does show the bones, but in patients below the age of eight, an MRI typically requires general anesthesia, and it is not necessary for the diagnosis. The resolution of the MRI is also not sufficient in young children to use in planning treatment in many cases.
In simple cases where the extra digit is attached to the hand by a small skin bridge, removal of the extra digit can be done in the office with a cautery device. This can be done within a few days of a newborn’s delivery. It is quick and painless after the initial numbing medicine is applied. Many centers will tie off the extra finger in the nursery, resulting in swelling, redness, and eventually the death of the finger or toe over up to several weeks until it falls off, leaving an often painful nerve stump at the base. We do not recommend allowing this to be done to your child.
For larger fingers or toes, surgery is recommended. We suggest waiting until the child is at least six months old, or ideally 18 to 24 months of age. Removal of the extra digit is more complicated than just cutting it off. Because some of the parts are shared between fingers or toes, surgery requires moving parts from the digit to be removed into the digit next to it to make the remaining finger or toe function and look better. (Find a doctor at HSS who treats polydactyly of the fingers or toes.)
For example, two thumbs can be combined into one using parts of the nails from both thumbs to get a wider nail and a wider thumb overall.
There are three reasons to remove extra fingers:
Prognosis is excellent for small extra digits or digits that branch away from a joint, as these can easily be removed. More complicated polydactyly can have good results, but joint motion, stability, and appearance are sometimes a concern. About 30% of patients will require more than one surgery to optimize outcomes.