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

You can have peace of mind knowing that the skilled experts in our Hand and Orthopedic Upper Extremity Program have treated thousands of babies and children with many bone-related conditions. We provide expert diagnosis, treatment, and care, and we benefit from our advanced clinical and scientific research.

If your child has mild thumb hypoplasia, they may undergo a course of occupational therapy, which will help improve the function of the thumb. The Occupational Therapy Program at Boston Children’s Hospital is dedicated to collaborating with you and your child’s doctor to provide the best possible care for your child.

Treatment programs are based on thorough evaluations and are always individualized to meet the needs of your child.