What Is Thumb Hypoplasia? Babies with thumb hypoplasia are born with a thumb that is smaller than normal, or with the thumb missing completely. Sometimes the bones of the wrist or arm are smaller or missing too. Thumb hypoplasia can happen on one or both hands. What Causes Thumb Hypoplasia? Thumb hypoplasia (also called hypoplastic thumb) happens before a baby is born. When a baby's hands are first forming, they are shaped like mittens. Then the fingers and thumb develop. In babies with thumb hypoplasia, the thumb does not form completely. Thumb hypoplasia is not caused by anything a mother did or did not do while pregnant. Who Gets Thumb Hypoplasia? Any baby can be born with thumb hypoplasia . Sometimes, it happens as part of a genetic syndrome . How Is Thumb Hypoplasia Diagnosed? A prenatal ultrasound might show thumb hypoplasia. 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. Other tests might be done to see if the thumb hypoplasia is part of a genetic syndrome. How Is Thumb Hypoplasia Treated? The thumb is a very important part of the hand. Surgery is usually recommended to improve a small or weak thumb. If the thumb is missing, the index finger can be made into a new thumb (this is called pollicization ). After surgery, occupational therapy (OT) and home exercises can help a child learn to use the thumb. Looking Ahead After treatment, most children with thumb hypoplasia learn to do all the usual things that kids do. Offer support as your child learns how to use his or her hands well. Back to Articles Related Articles Thumb Duplication Babies with thumb duplication (or thumb polydactyly) are born with an extra thumb on one or both hands. Most will have surgery to fix the problem. 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 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 Syndactyly Syndactyly is when a baby is born with two or more fingers or toes joined or "webbed" together. Read More 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 Symbrachydactyly Babies with symbrachydactyly are born with short often webbed fingers. Some might be missing fingers. 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 Occupational Therapy Occupational therapy can help improve kids' cognitive, physical, and motor skills and build their self-esteem and sense of accomplishment. 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 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.