Thumb Hypoplasia and Aplasia

What is thumb hypoplasia?

Thumb hypoplasia, also commonly called hypoplastic thumb, means that your child’s thumb is unusually small or underdeveloped. Thumb aplasia means that your child’s thumb is missing altogether.

In general, there are five types of thumb hypoplasia or aplasia:

Here are thumbs that suffer from thumb hypoplasia and aplasia.

  1. Your child’s thumb is slightly smaller than normal, but all of its structures — the bones, tendons, ligaments, muscles, and joints — are normal.
  2. Your child’s thumb is small and there are often minor abnormalities in the tendons and muscles within the thumb.
    • The middle joint of the thumb is unstable, causing the thumb to wobble. The web space between the thumb and index finger is tight and restricts movement.
    • The bones of your child’s thumb are abnormally small.
  3. There are abnormalities in many of the thumb's muscles along with a range of problems in the joints of the thumb and an abnormal tight web space between the thumb and index finger.
  4. Your child’s thumb is "floating" with no bony support and is attached to the hand by only skin and soft tissue.
  5. Your child’s thumb is missing.

What causes an underdeveloped or absent thumb?

Researchers still haven’t discovered the exact cause of this condition.

How common is an underdeveloped or absent thumb?

It’s rare, occurring in about 1 out of every 100,000 babies.

  • It can occur by itself or may be associated with other conditions where the radial side (thumb side) of the forearm does not develop properly.
  • These include Holt-Oram and Fanconi syndromes.
  • It’s also routinely seen with radial longitudinal deficiency.

In some cases, both the right and left hands may be affected.

What are the symptoms of thumb hypoplasia?

Because of the reduced functionality of your child’s thumb, they may have some problems with using their hand.

What’s going to happen to my child?

Children will adapt and can function without a missing finger. Children who have no use of a thumb will learn to rely on a lateral pinch between the long and index fingers.

However, they may have problems with fine motor activities such as pinching and grasping. It is these children who may require surgery to correct the problem.

How we care for thumb hypoplasia

The Orthopedic Center’s Hand and Orthopedic Upper Extremity Program and our Department of Plastic and Oral Surgery's Hand and Reconstructive Microsurgery Program have treated thousands of babies and children with thumb hypoplasia and other hand problems. We are experienced treating conditions that range from routine to highly complex, and can provide your child with expert diagnosis, treatment, and care. We also offer the benefits of some of the most advanced clinical and scientific research in the world.

Our Orthopedic Center is nationally known as the preeminent center for the care of children and young adults with a wide range of developmental, congenital, neuromuscular, sports related, traumatic, and post-traumatic problems of the musculoskeletal system.

Our Department of Plastic and Oral Surgery is one of the largest and most experienced pediatric plastic and oral surgery centers anywhere in the world. We provide comprehensive care and treatment for a wide variety of congenital and acquired conditions, including hand deformities.