What is polydactyly?

Polydactyly is a deformity in which the hand has one or more extra fingers in any of three places of the hand:

  • on the small finger side — most common (ulnar)
  • on the thumb side, also called thumb duplication — less common (radial)
  • in the middle of the hand — least common (central)

This condition is one of the most common congenital hand defects, affecting about one out of every 500 to 1,000 babies. Usually, only one of a child’s hands is affected. African-American children are more likely to have an extra little finger, while Asians and Caucasians are more likely to have an extra thumb.  

Your child’s doctor will know by sight that your baby’s hand has an extra digit. The doctor will refer you to a hand specialist, who will guide you to a more detailed diagnosis and treatment plan.


What are the symptoms of polydactyly and the different degrees of severity?

The extra fingers are usually smaller and abnormally developed than normal and can be made up of:

  • skin and soft tissue — the simplest to remove
  • skin, soft tissue, and bone but no joint — more challenging to remove/remodel
  • skin, soft tissue, and bone with joint (closer to a fully-formed finger — most challenging to remove/remodel)


What causes polydactyly?

During normal embryonic development (while the baby is still in the womb), the hand initially forms in the shape of a paddle, and then eventually — in about the sixth or seventh week of gestation — splits into separate fingers. Polydactyly results if there’s an irregularity in this process: An extra finger forms when a single finger splits in two.

The vast majority of occurrences of polydactyly are sporadic, meaning that the condition occurs without an apparent cause — while some may be due to a genetic defect or underlying hereditary syndrome. African-Americans are more likely to inherit the condition than other ethnic groups.

How we care for polydactyly

The skilled experts in the Boston Children's Hospital Hand and Orthopedic Upper Extremity Program and the Hand and Microsurgery Reconstructive Program have treated thousands of babies and children with hand problems, ranging from the simple to the highly complex. So we can provide your child with expert diagnosis, treatment, and care — as well as the benefits of some of the most advanced clinical and scientific research in the world.