Polydactyl means “many digits.” It comes from the Greek words “poly” (many) and “daktylos” (finger or toe), and it describes any person or animal born with more than the usual number of fingers or toes. The medical term for the condition is polydactyly, and it’s one of the most common limb differences present at birth, occurring in roughly 1 to 2 out of every 1,000 live births depending on the population.
Where Extra Digits Appear
Extra digits don’t show up randomly. They follow predictable patterns based on which side of the hand or foot they develop on, and doctors classify them into three types.
Postaxial polydactyly is the most common form. The extra digit appears on the pinky side of the hand or the outer edge of the foot. Preaxial polydactyly involves an extra digit on the thumb side of the hand or near the big toe. Central polydactyly is the rarest type, where the extra digit grows between the second and fourth fingers or toes.
The extra digit itself can range from a small, soft nub of tissue with no bone inside to a fully formed, functional finger or toe with its own joints, tendons, and blood supply. Some are connected to the hand only by a thin stalk of skin, while others share bone and cartilage with the neighboring digit.
How Common It Is
Polydactyly rates vary significantly across ethnic groups. A large study in New Zealand tracking births from 2010 to 2022 found an overall rate of 13 per 10,000 live births. European populations in that study had a lower incidence of about 6.3 per 10,000 births, while Māori, Pacific Islander, and Asian populations all had higher rates. Studies from the United States have consistently shown that postaxial polydactyly is roughly ten times more common in Black infants than in white infants, making it one of the most notable demographic patterns in birth differences.
What Causes Extra Digits
Polydactyly happens when something goes slightly off-course in the signaling process that shapes a baby’s hands and feet during early development. Your limbs form through a tightly choreographed cascade of molecular signals that tell cells where to grow and what to become. One of the key players is a signaling pathway that controls how digits are spaced and numbered. When mutations affect the genes involved in this pathway, cells receive instructions to build an additional digit.
The gene most commonly linked to isolated polydactyly (meaning extra digits without other health issues) is called GLI3. This gene helps regulate the same developmental pathway that patterns the brain and limbs before birth. Different mutations in GLI3 can produce different forms of polydactyly, from an extra pinky-side digit to extra digits near the thumb combined with webbing between fingers.
Most cases of isolated polydactyly follow an autosomal dominant inheritance pattern, which means a child only needs to inherit one copy of the altered gene from one parent to develop the trait. If one of your parents has polydactyly, you have roughly a 50% chance of inheriting it. That said, the trait can also appear spontaneously in families with no prior history.
Polydactyly as Part of a Syndrome
In most cases, extra digits are an isolated finding and the child is otherwise completely healthy. Sometimes, though, polydactyly appears alongside other features as part of a broader genetic syndrome. One well-known example is Ellis-van Creveld syndrome, where extra digits on the pinky side of the hands (present in about 98% of cases) occur together with short stature, shortened limbs, heart defects, and nail abnormalities.
Other syndromes associated with polydactyly include conditions that cause skeletal abnormalities, narrow rib cages, or kidney and liver problems. This is why doctors typically examine a newborn with extra digits carefully, looking for any additional signs that might point to a syndrome rather than isolated polydactyly. For the vast majority of babies born with extra fingers or toes, no other issues are found.
How It’s Detected Before Birth
Extra digits can often be spotted on a routine prenatal ultrasound. Most cases are identified between 17 and 23 weeks of pregnancy, when the baby’s hands and feet are developed enough to count individual digits on the screen. If polydactyly is detected, your doctor may recommend additional imaging or genetic testing to check whether the extra digits are isolated or part of a syndrome.
How Extra Digits Are Treated
Treatment depends entirely on the complexity of the extra digit. Small, dangling digits connected only by a narrow stalk of skin are sometimes tied off shortly after birth, cutting off blood flow so the tissue falls away on its own. Fully formed extra digits with bone, joints, and tendons require surgical removal and reconstruction.
Most surgeons recommend operating between 12 and 18 months of age. At that point, anesthesia risks are lower, the child’s hands are large enough to work on more precisely, and the child hasn’t yet developed fine motor skills or self-awareness about their hand’s appearance. Some surgeons prefer operating as early as 7 to 12 months, while others wait until 12 to 16 months because slightly larger digits are technically easier to reconstruct.
The surgery typically involves removing the less developed digit and using its tissue to improve the remaining one. For thumb duplications, the surgeon often keeps the digit that has better alignment and function, then rebuilds the ligaments and tendons to create a stable, well-shaped thumb. In cases where both duplicated digits are roughly equal, a surgeon may take the best portions of each and combine them into a single digit.
What to Expect After Surgery
Surgical correction produces good functional results for most children, but it’s worth knowing that long-term complications are not uncommon. A review of 249 cases by the American Association for Hand Surgery found that about 35% developed some kind of long-term issue. The most frequent problem was a residual angular deformity, where the reconstructed digit angles slightly to one side (accounting for about 58% of complications). Joint instability or stiffness made up another 30%. Many of these issues are mild and don’t significantly affect hand function, but some children need a second procedure as they grow.
Polydactyl Cats
If you searched “polydactyl,” there’s a good chance you were thinking about cats. Polydactyl cats are born with extra toes, most commonly on their front paws, giving them wide, mitten-like feet. The trait comes from a mutation in a regulatory sequence that controls the same limb-patterning signals involved in human polydactyly. Because the mutation affects a regulatory switch rather than a protein directly, the number and placement of extra toes varies widely, even among kittens in the same litter.
These cats are sometimes called “Hemingway cats” after the American author Ernest Hemingway, who was given a six-toed cat named Snow White by a ship captain. After Hemingway’s death in 1961, his Key West home became a museum that still houses around 50 descendants of his original cats. Roughly half of them are polydactyl. The nickname stuck, and Hemingway’s well-publicized love for his extra-toed cats helped turn polydactyly from an obscure genetic curiosity into something people actively seek out in pets.
Polydactyly in cats is harmless. The extra toes are fully functional, and many owners report that polydactyl cats have an easier time gripping toys, climbing, and opening doors. The trait follows dominant inheritance in cats just as it does in humans, so breeding a polydactyl cat with a normal-toed cat gives each kitten about a 50% chance of having extra toes.