Syndactyly (plural: syndactylies) refers to a congenital fusion of two or more digits. It may be confined to soft tissue (soft tissue syndactyly / simple syndactyly) or may involve bone (bony syndactyly / complex syndactyly).

Epidemiology

The overall estimated incidence is at ~1 per 2500 to 5000 live births ^6,8. There may be a greater male predilection.

Associations

Syndactyly can occur as an isolated phenomenon or can be associated with numerous other entities. Isolated cases can be either sporadic or familial.

• aneuploidic syndromic

  • triploidy: tend to affect the 3^rd and 4^th digits of the hands

  • Down syndrome ¹⁰

• non-aneuploidic syndromic

  • acrocephalosyndactylies

    • type I: Apert syndrome

    • type II: Crouzon syndrome

    • type III: Saethre-Chotzen syndrome

    • type V: Pfeiffer syndrome

  • acrocephalopolysyndactylies

    • type I: Noack syndrome

    • type II: Carpenter syndrome: typically gives soft tissue syndactyly

    • type III: Sakati-Nyhan syndrome

    • type IV: Goodman syndrome

  • amniotic band syndrome ³

  • Fraser syndrome / cryptophthalmos syndrome ⁴

  • Gorlin syndrome

  • Greig cephalopolysyndactyly syndrome ⁵

  • macrodystrophia lipomatosa

  • neurofibromatosis type 1 ¹¹

  • Pallister-Hall syndrome

  • Poland syndrome

  • proximal radioulnar synostoses: Cenani Lenz syndactyly

  • prune belly syndrome

  • Roberts syndrome

  • VACTERL association

• non-syndromic

  • isolated polydactyly, a.k.a. polysyndactyly

  • isolated brachydactyly, a.k.a. brachysyndactyly

  • isolated ectrodactyly

Pathology

There is a very wide spectrum of syndactyly ranging from partial to complete.

Location

Overall, the 2^nd and 3^rd digits tend to be most frequently associated ⁶. May involve the toes more than the fingers.

Radiographic features

Plain radiograph

Postnatally the type and degree of bony syndactyly can be easily diagnosed on plain film.

Ultrasound

Often difficult to diagnose on ultrasound (especially with soft tissue syndactyly). The diagnosis may be suggested if the digits appear to constantly move together ⁷. The fingers may appear constantly deformed with complex syndactyly ⁶.

Treatment and prognosis

The overall prognosis can be extremely variable depending on the presence of other associated anomalies.

History and etymology

The term syndactyly is derived from the Greek words "syn" meaning together and "daktulos" meaning fingers.

See also

• symphalangism