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 syndrome . 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. Back to Articles Related Articles Polydactyly Polydactyly is when a baby is born with an extra finger on the hand or an extra toe on the foot. It can be on one or both hands or feet. Read More Thumb Hypoplasia Babies with thumb hypoplasia are born with a thumb that is smaller than normal, or with the thumb missing completely. Read More Syndactyly Syndactyly is when a baby is born with two or more fingers or toes joined or "webbed" together. Read More Symbrachydactyly Babies with symbrachydactyly are born with short often webbed fingers. Some might be missing fingers. Read More Bones, Muscles, and Joints Without bones, muscles, and joints, we couldn't stand, walk, run, or even sit. The musculoskeletal system supports our bodies, protects our organs from injury, and enables movement. Read More Occupational Therapy Occupational therapy can help improve kids' cognitive, physical, and motor skills and build their self-esteem and sense of accomplishment. Read More Ulnar Dysplasia Babies with ulnar dysplasia (also called ulnar club hand) are born with a short or missing ulnar bone. This makes the wrist turn out. Read More Radial Dysplasia Babies with radial dysplasia (also called radial club hand) are born with a short or missing radial bone. This makes the wrist turn in. Read More X-Ray Exam: Finger Doctors may order a finger X-ray to find the cause of symptoms such as pain, tenderness, or swelling, or to detect broken bones or dislocated joints. Read More X-Ray Exam: Hand A hand X-ray can help find the cause of pain, tenderness, swelling, and deformity. It also can detect broken bones or dislocated joints. Read More Note: All information is for educational purposes only. For specific medical advice, diagnoses, and treatment, consult your doctor. © 1995-2021 KidsHealth®. All rights reserved. Images provided by The Nemours Foundation, iStock, Getty Images, Veer, Shutterstock, and Clipart.com.