Polydactyly is the term for when someone has extra digits, or fingers or toes. It usually means that a baby is born with at least six fingers on one or both hands or six toes on one or both feet.
It's one of the most common limb differences, affecting one out of every 500 to 1,000 babies. It doesn't usually cause any health problems for the child as they grow up.
What Does Polydactyly Look Like?
An extra digit can appear on one hand or foot or both hands or feet. It rarely happens on both hands and both feet.
The extra digit isn’t usually a fully functional finger or toe. It tends to be smaller than the other digits. It's usually a partially developed digit that doesn't bend or grip the way the rest of the digits do.
Some extra digits are only skin and soft tissue that protrude from the hand or foot. They can vary in size. Some are just a bump on the hand or foot, while others are longer.
Other extra digits have skin, soft tissue, and bone underneath. In some cases, there’s a joint as well as a bone. These are more like regular digits.
What Are the Types of Polydactyly?
There are three kinds of polydactyly that differ based on where the extra toe or finger is located on the hand or foot:
- Preaxial polydactyly — The extra finger is outside the thumb (radial polydactyly) and the extra toe is outside the big toe (tibial polydactyly).
- Postaxial polydactyly — The extra finger is outside the little finger (ulnar polydactyly) and the extra toe is outside the little toe (fibular polydactyly).
- Central polydactyly — The extra finger is between other fingers and the extra toe is between other toes.
What Is the Cause of Polydactyly?
Polydactyly develops when a baby is developing in the womb. Hands and feet begin as flat, paddle-like extremities until the fingers and toes start to separate, which usually happens around week 6 of pregnancy. A digit will split into two parts in some cases instead of forming a single finger or toe.
Polydactyly can run in families, but it doesn't always. In many cases, polydactyly happens spontaneously without a genetic cause. The child won't have any other developmental differences besides the extra digit.
There are some underlying conditions, however, for which polydactyly is a symptom. These conditions include McKusick-Kaufman syndrome, Pallister-Hall syndrome, and Bardet-Biedl syndrome. If your child has other physical or developmental differences, you can talk to your doctor about the cause. You may need further testing to check for other health conditions in your child.
What Is the Treatment for Polydactyly?
Your doctor will usually recommend polydactyly surgery for removing extra fingers or toes when your child is between ages 1 and 2. The goal of surgery is to provide your child with hands and feet that look normal and function normally. Doing surgery while your child is still young helps in making sure that they don't miss any milestones related to using their hands or feet.
The doctor will examine your child to determine whether there’s a joint or bone in the extra digits. They may need to get an X-ray to understand how the extra digit is attached. That will help your doctor decide the kind of procedure that is needed. That may include:
- Vascular clip — If the extra digit doesn't have a bone, the doctor will tie off the base of the digit. This will cut off the blood supply, so the extra skin dies and falls off. It's similar to how a baby's umbilical stump falls off after birth.
- Surgery — If there’s a bone or ligament in the extra digits, your doctor will need to do surgery. In uncomplicated cases, the doctor can remove the extra digit without having to reconstruct any part of your child's hand or foot. Your child will need to wear a splint or cast while the hand or foot heals.
- Surgery with reconstruction — If the bone or ligament of the extra digit affects how the rest of the hand or foot works, the surgery may be more complex. The doctor will carefully remove the extra digit and re-route any affected bones, tendons, or ligaments to make sure that the hand or foot functions well. Your child may need physical or occupational therapy to strengthen their hand or foot after a complex surgery.
Some children need only one procedure to correct an extra digit, while some others may need additional procedures later to improve how their hand or foot works. Your doctor will talk to you about what will help your child with recovery and any future procedures they might need.