Isabelle presented to the office with her mother with a presenting complaint of no thumbs on either hand. Our discussion was long and involved about the role the thumb plays in opposition and the importance of opposition in accomplishing everyday tasks of living. Her mother was quite interested in surgical reconstruction of the hand to include pollicization of the index fingers into the position of a thumb. Towards the end of the visit, her mother acknowledged that indeed a full and complete life can be achieved without thumbs as she showed me her own hands, neither of which had a thumb. “If you’ve done so well without thumbs why would you want Isabelle to go through this kind of a surgery” I asked. Her response was “I’ve spent my whole life having to explain how I do things, I don’t want her to have to answer those kinds of questions.”

What is thumb hypoplasia?

  • Hypo = low or under
  • Plasia = development

Thumb hypoplasia presents in various degrees of severity. Some children have a small but functioning thumb while others lack any thumb structures. The ability to move the thumb to touch the small finger is called opposition. The presence of an opposable thumb is considered important for manipulation of most objects. However, children born without thumbs often adapt to the condition very well with few limitations.

Some hypoplastic thumbs have small metacarpal bones and lack typical ligaments and muscles which make the thumbs unstable and weak.

Hypoplastic thumbs are categorized depending on their shape and stability.

  • Type 1 – minimal shortening and weakness
  • Type 2 – instability with weakness
  • Type 3A – very small bone structures with stable base
  • Type 3B – very small bone with unstable base
  • Type 4 – floating thumb
  • Type 5 – absent thumb

How is thumb hypoplasia diagnosed?

X –rays define the actual boney elements that are present or absent, but a clinical exam by a pediatric hand specialist is required to determine the stability and ability of the thumb.

How common is thumb hypoplasia?

Thumb hypoplasia is rare, occurring in approximately 1 out of 100,000 births. 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. It can occur unilaterally or bilaterally.

How is thumb hypoplasia treated?

When the hypoplasia is minimal, the child may benefit from hand therapy to strengthen muscles and to maximize ability.

Reconstruction for thumbs with weakness and instability includes surgical procedures, called opponensplasties, that provide support to both the ligaments and muscles to give the thumb more strength. These procedures include moving tendons or muscles from other parts of the hand to replace the weak structures. Although the donor sites may show some minimal change in function, the overall improvement in hand strength makes up for any minor change.

Pollicization is a surgical procedure that creates a thumb out of an index finger. This involves moving, rotating, and shortening the index finger into a position where it can serve as a thumb for power and fine motor skills in grasp. This is most commonly used for patients who are born with no thumb or only a dangling, tiny thumb. During pollicization the index finger metacarpal bone is cut and the finger is rotated approximately 120 to 160 degrees and replaced at the base of the hand at the usual position of the thumb. The arteries and veins are left attached. Tendons from the migrated index finger may be shortened and rerouted to provide good movement.

Who benefits from pollicization versus reconstruction?

For the child whose hand shows good metacarpal bulk and reasonable stability at the metacarpal base, reconstruction with opponensplasty is a good solution. For kids with small metacarpal bones and a lack of stability at the base of the thumb, pollicization usually results in a hand with better strength and function.

The 3b thumb with its inadequate bone and stability is a poor candidate for opponensplasty. The long term results of surgical procedures aimed at stabilizing the 3B thumb are poor and disappointing with most children ignoring the thumb entirely and substituting a side-to-side pinch pattern between the index and middle fingers that have better strength and stability. Because there are some thumb structures present, removing this poorly functioning digit and replacing it with the index finger is an emotional decision for parents. After being presented with the facts and recommendations from the hand surgeon regarding pollicization, we find that most parents make the choice with their hearts.

For pollicization, the best results occur if the surgery is performed before the child is 2 years old. This allows the brain to ‘reprogram’ the index finger to function as a thumb. Opponensplasties should be delayed until the bone structures of the thumb are large enough to accommodate the tendon transfers. For most children this would be between the ages of 5 – 8 years old.

What is the long-term outlook for my child?

Adaptation is the hallmark of childhood. Even without a thumb a child can lead a productive, healthy life. After surgical reconstructions and therapy, most children use the thumb normally. Cosmetically, the results are surprisingly good as most people do not notice whether a hand has a thumb and three fingers or a thumb and four fingers. What people see is whether the thumb and fingers work in a typical pinch pattern. As long as the thumb opposes the fingers, the hand is perceived as normal.

At 20 months of age Isabelle underwent her first pollicization. During hand therapy, she quickly adapted a typical use pattern in her reconstructed thumb. At 24 months of age, the opposite hand was treated with a pollicization as well. Her family is delighted with her function and appearance. On a recent follow-up visit when Isabelle was 5, her mother said smiling, “the substitute kindergarten teacher did not even notice that Isabelle has only 3 fingers and a thumb on each side. No one ever asks her questions about her hands”.