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Thumb Duplication

What Is Thumb Duplication?

Babies with thumb duplication (or thumb polydactyly) are born with an extra thumb on one or both hands. The two thumbs on one hand can be joined or webbed together.

A thumb duplication is more of a split thumb rather than an "extra thumb." When it affects one hand, both thumbs on that hand are usually smaller and less developed than the thumb on the hand that is not affected.

What Causes Thumb Duplication?

Thumb duplication happens before a baby is born. When a baby’s hands are first forming, they are shaped like mittens. Then the fingers split. An extra split can result in thumb duplication. The reason this happens is not known. It is not caused by anything a mother did or did not do while pregnant.

Who Gets Thumb Duplication?

Any baby can be born with thumb duplication. It sometimes runs in families. Most babies who have thumb duplication do not have other health problems. But sometimes, thumb duplication happens as part of a genetic


How Is Thumb Duplication Diagnosed?

A prenatal ultrasound might show a thumb duplication. Otherwise, doctors diagnose it when a baby is born.

X-rays of the bones in the thumbs and hands will help the surgeon decide on the best kind of treatment.

How Is Thumb Duplication Treated?

Most babies with thumb duplication get surgery. The surgery removes the extra thumb and, if needed, rebuilds the remaining thumb. The hand is usually put in a cast for a few weeks after surgery.

Occupational therapy (OT) and home exercises can help if a child needs help to learn to use the thumb.

Looking Ahead

After recovered from surgery, your child can do all of the usual things that kids do. Offer your support as your child learns how to use his or her hands well.