The name comes from the Greek poly (many) and dactylos (finger). The extra fingers or toes are described as "supernumerary," which means "more than the normal number." For this reason, the condition is sometimes called supernumerary digit.
A range of treatments is available depending on the type of polydactyly, and the cause is often genetic.
What are the symptoms?
Small finger duplication is the most common form of polydactyly.
Image credit: Radke / Otis Historical Archives of "National Museum of Health & Medicine". (1979, September)
Polydactyly is a condition where a person is born with extra fingers or toes on one or both of their hands and feet.
The way polydactyly presents can vary. It may appear as a:
- small, raised lump of soft tissue, containing no bones (called a nubbin)
- partially formed finger or toe containing some bones but no joints
- fully functioning finger or toe with tissues, bones, and joints
There are three main types including:
- Ulnar or postaxial polydactyly or small finger duplication: This is the most common form of the condition, where the extra finger is on the outside of the little finger. This side of the hand is known as the ulnar side. When this form of the condition affects the toes, it is called fibular polydactyly.
- Radial or preaxial polydactyly or thumb duplication: This is less common, occurring in 1 in every 1,000 to 10,000 live births. The extra finger is on the outside of the thumb. This side of the hand is known as the radial side. When this form of the condition affects the toes, it is called tibial polydactyly.
- Central polydactyly: This is a rare type of polydactyly. The extra finger is attached to the ring, middle, or most often index finger. This form of the condition has the same name when it affects the toes.
Polydactyly may be passed down in families.
When polydactyly is passed down, it is known as familial polydactyly. This form of polydactyly typically happens in isolation, meaning a person may not experience any associated symptoms.
Polydactyly may also be associated with a genetic condition or syndrome, which means it may be passed down along with a genetic condition. If polydactyly is not passed down, it occurs due to a change in a baby's genes while it is in the womb.
Conditions associated with polydactyly include:
- syndactyly (webbed hands or feet)
- asphyxiating thoracic dystrophy
- Carpenter syndrome
- Ellis-van Creveld syndrome (chondroectodermal dysplasia)
- Laurence-Moon-Biedl syndrome
- Rubinstein-Taybi syndrome
- Smith-Lemli-Opitz syndrome
- trisomy 13
Some types of polydactyly are more likely to be passed down. Others are more likely to be associated with a genetic condition.
Small finger duplication is often hereditary. This form of the condition is 10 times more common among African-American people than other groups.
In African-Americans, small finger duplication tends to occur in isolation, inherited from a specific dominant gene. In Caucasians, it is more likely to be associated with a genetic condition or syndrome.
Thumb duplication often occurs in isolation and on only one hand or foot.
People who have central polydactyly may also have webbed hands or feet.
How is it diagnosed?
An X-ray may be used to diagnose polydactyly of fingers or toes.
Image credit: Hellerhoff, (2011, January).
Doctors will examine a person and use X-ray imaging to diagnose polydactyly. This helps them to see the bone structure of the affected hand or foot.
Each type of polydactyly has subtypes that depend on how formed the extra digit is and where it is positioned. An X-ray helps the doctor to identify these.
The doctor will also ask questions about their family and medical history to help them to diagnose the cause.
Questions may include:
- Does anyone else in the family have additional fingers or toes?
- Is there a family history of genetic conditions?
- Are there other symptoms or health concerns?
A doctor may also carry out further tests including:
- chromosome studies
- enzyme tests
- metabolic studies
Sometimes, polydactyly is diagnosed during the first 3 months of pregnancy. This is done using an ultrasound or embryo fetoscopy.
Treatment depends on which type of the condition a person has:
Small finger duplication
Small finger duplication may not require treatment, as it does not usually affect how people can use their hand. However, they may still want to treat it for cosmetic reasons.
If an extra small finger is only partially formed and does not contain any bones, it may be easy to remove. A doctor may do this by tying a tight string around the base of the extra finger. This cuts off the blood supply, allowing excess soft tissue to fall away naturally. This procedure often takes place in the first year after birth.
If an extra small finger is more fully-formed or functional, it may require surgery to remove.
Treatments for thumb duplication are more complicated because the extra thumb may affect the function of the other thumb.
For this reason, it may not be possible to remove the extra thumb simply. Surgery may be needed to reconstruct one functioning thumb, using parts of both thumbs.
There are a variety of different surgical options available depending on the position and formation stage of the extra thumb.
Central polydactyly may lead to a fully-functioning extra finger. In this case, removal would be needed only if the person desired the digit to be removed.
Image credit: Wilhelmy, (2014, March 2).
There are some surgical options for central polydactyly. These include:
- keeping the additional central finger, but operating on tendons and ligaments to avoid deformities
- removing the extra central finger and reconstructing the one it is attached to
- removing both fingers and reconstructing one new finger
The doctor will discuss these options with the person who has polydactyly. Together they can decide the most appropriate treatment.
Are there any complications?
Complications from surgery are rare but may include:
- risk of infection
- tender lump where the digit or nubbin has been removed
- restricted movement of the reconstructed digit
There are many surgical options available for polydactyly. Most are simple and usually have positive outcomes.
Small finger duplication, which is the most common type of polydactyly, may not require treatment. If it does, this is generally for cosmetic reasons.
If someone has polydactyly due to an underlying genetic condition, this may require additional treatment. A doctor can help a person find the best way to manage their condition.