Polydactyly: Definition, Symptoms, Causes, Types and Treatment

It is when a baby is born with an extra finger on the hand or an extra finger on the foot. It can be on one or both hands or feet.


Polydactyly usually occurs on the side of the little finger or on the side of the little toe (called “post-axial”).

Less commonly, it occurs on the side of the thumb or big toe (“pre-axial”). In rare cases, it can be central or in the middle of the hand or foot. The extra digit is generally smaller than the other fingers and toes.

What are the different degrees of severity?

The extra fingers usually develop smaller than normal and abnormally. These can be made up of:

  • Skin and soft tissue: the simplest to remove.
  • Skin, soft tissue and bones, but no joints –  more difficult to remove / fix.
  • Jointed Skin, Soft Tissue and Bone – Closer  to a fully formed finger, harder to remove / fix.

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, around the sixth or seventh week of gestation, it divides into separate fingers.

Polydactyly occurs if there is an irregularity in this process: an extra finger is formed when a single finger splits into two.

Any baby can be born with polydactyly. Posaxial polydactyly can run in families. The vast majority of occurrences of polydactyly are sporadic, meaning that the condition occurs without an apparent cause, but some may be due to a genetic defect or the underlying inherited syndrome.

African Americans are more likely to inherit the condition than other ethnic groups

How is it diagnosed?

Polydactyly can be seen before birth on an ultrasound. Otherwise, doctors diagnose it immediately when the baby is born. Sometimes doctors take X-rays to see if the extra digit has bones and joints. This helps the surgeon decide what type of treatment is needed.

What are the types of polydactyly?

Polydactyly ranges from an extra piece of soft tissue (skin) that has no bone inside to a complete duplication of a finger or toe.

  • Thumb Duplication: There are different levels of duplication depending on which bone of the thumb is divided. The thumb may have 3 bones instead of two, this is called a triphalangeal thumb.
  • Duplication of the index, middle, or ring finger (central duplication): occasionally occurs with syndactyly (webbed / fused fingers).
  • Little finger duplication

How common is it?

  • Polydactyly of the thumb: Duplication of the middle thumb bone is the most common form (43%). The extra bone in the thumb (triphalangeal thumb) is the next most common (20%). This occurs in 1 out of every 3,000 births.
  • Central Duplication: The most common duplication in the ring finger, then the long finger, then the index finger (which is rarely duplicated). Central duplication often occurs in both hands and often occurs in conjunction with syndactyly. Many patients have polydactyly or syndactyly that affects the feet as well.
  • Little finger duplication – the most common form of polydactyly, 8 times more common than the other types. It often happens in both hands.

Because it happens?

  • Thumb Duplication – Usually occurs randomly, with the exception of the triphalangeal thumb which is inherited.
  • Central mirroring: sometimes inherited.
  • Little finger duplication : Like the central duplication, this one is also commonly inherited.

How is polydactyly treated?

Treatment of polydactyly depends on the location of the finger or toe and how it is formed. An extra pinkie or little toe that is connected with a thin stem can be easily removed, sometimes directly at the surgeon’s office with a surgical clip or stitch.

Extra thumbs, big toes, or middle fingers or toes that contain bones and / or joints need surgery in the hospital.

What is done after the surgery?

Because polydactyly surgery is usually done when a baby is young, most children learn to use their hands and walk without problems. If necessary, occupational therapy, physical therapy, and home exercises can help a child with this.