Syndactyly is often found during a child's health exam. In its most common form, webbing occurs between the 2nd and 3rd 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 most often go up to the first joint of the finger or toe. However, they can run the length of the finger or toe.

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

More common causes include:

• Down syndrome
• Hereditary syndactyly

Very rare causes include:

• Apert syndrome
• Carpenter syndrome
• Cornelia de Lange syndrome
• Pfeiffer syndrome
• Smith-Lemli-Opitz syndrome
• Use of the medicine hydantoin (phenytoin) during pregnancy (fetal hydantoin effect)

This condition is normally discovered at birth while the baby is in the hospital.

Your health care provider will perform a physical exam and ask 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 present?

An infant with webbing may have other symptoms that together may be signs of one syndrome or condition. That condition is diagnosed based on a family history, medical history, and physical exam.

The following tests may be done:

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

Surgery may be done to separate the fingers or toes.

Syndactyly; Polysyndactyly

Carrigan RB. The upper limb. In: Kliegman RM, St. Geme JW, Blum NJ, Shah SS, Tasker RC, Wilson KM, eds. Nelson Textbook of Pediatrics. 21st ed. Philadelphia, PA: Elsevier; 2020:chap 701.

Mauck BM. Congenital anomalies of the hand. In: Azar FM, Beaty JH, eds. Campbell's Operative Orthopaedics. 14th ed. Philadelphia, PA: Elsevier; 2021:chap 80.

Son-Hing JP, Thompson GH. Congenital abnormalities of the upper and lower extremities and spine. In: Martin RJ, Fanaroff AA, Walsh MC, eds. Fanaroff and Martin's Neonatal-Perinatal Medicine. 11th ed. Philadelphia, PA: Elsevier; 2020:chap 99.

Updated by: Neil K. Kaneshiro, MD, MHA, Clinical Professor of Pediatrics, University of Washington School of Medicine, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.