Thumb duplication (pre-axial polydactyly)

Some children are born with a second thumb, a congenital condition also known as pre-axial polydactyly or first-digit duplication.

About thumb duplication in kids

Thumb duplication is one of the more common physical abnormalities in the hand . Duplicated thumbs can vary widely in appearance. A child might have an extra thumb on one or both hands. The two thumbs might be joined or webbed, and often the thumbs are smaller or underdeveloped. While it might look like two thumbs, the thumb is often split, with both digits sharing the bones, muscles, tendons, ligaments and nerves that would normally be in a single thumb. 

Experts in thumb duplication

As the only comprehensive pediatric hand and upper extremity program in the state, Children’s Wisconsin provides expert care to kids and teens with a wide range of common and rare conditions affecting the shoulder, arm, elbow, wrist and hand. With our team’s specialized training, vast experience and deep knowledge of the unique challenges of children’s growing bodies, we can ensure the best possible outcomes for a child born with thumb duplication. As Wisconsin’s highest-rated pediatric surgery center, our board-certified surgeons use the most advanced techniques and technology. Our child-centered environment and wraparound services are designed to support the whole family and provide comfort during treatment and beyond. If your child has already been diagnosed at another center, we invite you to get a second opinion at Children’s Wisconsin.

What causes thumb duplication?

When a baby’s hands are developing in the womb, they start as a mitten shape and then develop into individual fingers. Sometimes an extra division occurs on the thumb side of the hand. Like other congenital defects, a baby’s anatomy can spontaneously develop abnormally with no known reason. Sometimes extra fingers and toes can run in families, and other times this condition is associated with genetic syndromes, such as Down syndrome.

Why is thumb duplication a concern?

Most of the time, kids with this condition don’t have other health problems. However, most families opt to surgically remove the extra thumb for cosmetic reasons as well as to maximize normal functional use of their child’s hand. An extra thumb can affect a child’s daily life in multiple ways, from how they grip a pencil as they first learn to write to how well gloves fit their hands. For that reason, it’s usually recommended that the extra thumb be removed early in childhood, before a child starts school.

How is thumb duplication diagnosed?

The doctor might spot a baby’s hand abnormality on a prenatal ultrasound, but often, this condition is discovered at birth. To determine the best course of treatment, our hand/upper extremity specialists will evaluate your child’s hand structure using imaging. At Children’s Wisconsin, we use imaging procedures that ensure your child is exposed to the smallest amount of radiation possible. Imaging procedures may include:

X-rays – Uses invisible electromagnetic energy beams to produce images of internal tissues, bones and organs onto film

Magnetic resonance imaging (MRI) – Uses a combination of large magnets, radio frequencies and a computer to produce detailed images of organs and structures within the body

Computed tomography scan (CT scan) – Uses a combination of X-rays and computer technology to produce detailed, cross-sectional images of the body, including the bones, muscles, fat and organs

Treatment for thumb duplication

Surgery is the recommended treatment in most cases. It’s usually done as an outpatient procedure when a child is ages 1-2. Our highly skilled pediatric hand surgeon will remove the extra thumb and then rebuild the remaining thumb so that it is complete, repairing the bones, tendons and soft tissue in a precise and delicate manner to preserve your child’s movement and function.

After surgery, your child will need to wear a cast for 2-4 weeks  to immobilize and protect their hand while it heals.

Hand therapy is a critical part of the postsurgical process to promote healing, increase range of motion and maximize functional use of your child’s hand. Our certified hand therapist offers serial casting, custom splinting, paraffin wax treatments, scar massage and more.

Long-term outlook for thumb duplication

With proper treatment by a pediatric hand surgeon, most cases of thumb duplication can be corrected and heal well. In some cases, a child might need another procedure to straighten the remaining thumb. Your child will need to continue to be monitored by a hand/upper extremity expert throughout early childhood to make sure their thumb is developing and functioning appropriately.