Webbing of the fingers and toes is called syndactyly. It refers to the connection of two or more fingers or toes. Webbing usually only involves a skin connection between the two areas, but in rare cases may involve the connection (fusion) of bones. 

Syndactyly may be discovered during an examination of an infant or child. In its most common form, it is seen as webbing between the second and third toes. This form is often inherited and is not unusual. Syndactyly can also occur along with other birth defects involving the skull, face, and bones.

The web connections usually run up to the first joint of the finger or toe, but may run the entire length.

"Polysyndactyly" describes both webbing and the presence of an extra number of fingers or toes.

Relatively common causes:

• Down syndrome
• Hereditary syndactyly

Extremely rare causes:

• Apert syndrome
• Carpenter syndrome
• Cornelia de Lange syndrome
• Pfeiffer syndrome
• Smith-Lemli-Opitz syndrome
• Using the medication hydantoin during pregnancy (Fetal hydantoin effect)

This condition is normally discovered at birth and evaluated during the newborn hospital stay.

The health care provider will perform a physical exam and ask questions about the child's medical history. Questions may include:

• Which fingers (toes) are involved?
• Have any other family members had this problem?
• What other symptoms or abnormalities are also present?

An infant with webbing may have other symptoms and signs that, when taken together, define a specific syndrome or condition. Diagnosis of that condition is based on a family history, medical history, and a physical exam.

The following tests may be done:

• Chromosome studies
• Lab tests to check for certain proteins (enzymes) and metabolic problems
• X-rays

Syndactyly; Polysyndactyly

Updated by: Deirdre O’Reilly, M.D., M.P.H., Neonatologist, Division of Newborn Medicine, Children’s Hospital Boston and Instructor in Pediatrics, Harvard Medical School, Boston, Massachusetts.