Thumb hypoplasia

What is thumb hypoplasia?

Thumb hypoplasia refers to an abnormally small, poorly developed thumb. When there is not a thumb on the hand, it is called thumb aplasia.

Thumb hypoplasia comes in different types. These types depend on the extent of underdevelopment:

• Type 1: Small but stable bones and normal muscles.

• Type 2: Small bones and muscles with an unstable thumb joint.

• Type 3: Similar to type 2, but the muscles are further affected or even absent.

• Type 4: A “floating” thumb connected to the hand by only skin and soft tissue.

• Type 5: Absence of the thumb (thumb aplasia).

How common is thumb hypoplasia?

• Rare: estimated to occur in about 1 out of every 100,000 babies.

• Boys and girls are affected equally.

• Over half (60%) of cases involve both hands.

What causes thumb hypoplasia?

The cause is unknown. Genetics are believed to be strongly involved. Thumb hypoplasia can occur alone, but it is most often part of a spectrum of conditions. Most cases are related to genetic conditions where the forearm fails to develop properly.

Your doctor may recommend genetic counseling to determine whether you child has one of these conditions.

What are the symptoms of thumb hypoplasia?

Children with thumb hypoplasia have a thumb that does not work properly. This makes it hard to grasp or pinch objects. Type 1 thumbs with hypoplasia retain the most function. Types 4 and 5 thumbs are not able to be used.

How is thumb hypoplasia diagnosed?

Thumb hypoplasia is typically diagnosed during the newborn exam. In addition to a medical history and physical examination, diagnostic procedures may include X-rays. X-rays provide further details of underlying tissues and help classify the type of this condition.

• X-ray: a test that uses invisible electromagnetic energy beams to produce images of internal tissues on film.

What is the treatment for thumb hypoplasia?

Treatment depends on the ability to use the thumb and the hand. A functional thumb is essential for a child to develop fine motor skills. Treatments reflect the importance of having a thumb that can be used:


• Non-surgical therapy: Children with only small bones (Type 1) or a tight webspace often do not require surgery. Instead, physical therapy alone may improve thumb function.

• Reconstructive surgery: Children with types 2 and 3 thumbs usually benefit from reconstructive surgery. Surgery is performed between the ages of 6 and 18 months. Surgery involves reconstructing an unstable thumb joint and releasing tight web spaces.

• Pollicization: More severe type 3, 4 and 5 thumbs may call for a surgical procedure called “pollicization.” In this operation, the index finger is transferred to the thumb position.

What is the long-term outlook for a child with thumb hypoplasia?

Long-term results depend on the condition of the remainder of the hand, wrist and forearm. Surgery cannot restore full strength to the thumb; however, fine motor tasks can show improvement. More difficult cases may require secondary operations to improve thumb function.