Non-Syndromic Syndactyly

Non-syndronomic syndactyly only involves the digit and results in appendage malformation. There are nine sub-groups (SD1 to SD9).

SD1

• Zygodactyly
• Varied phenotype - can affect upper and/or lower limbs
• In the hand, cutaneous or bony involvement of the 3rd or 4th web space
• Only autosomal dominant inheritance
• 4 sub-types (zygodactyly 1-4)

SD2

• Synpolydactyly
• Most heterogeneous malformations fo the non syndromic syndactylies
• Autosomal dominant inheritance
• 3rd and 4th finger syndactyly with polydactyly within the web space

SD3

• Complete syndactyly of the 4th and 5th digits 
• Bilateral 
• Most commonly a soft-tissue syndactyly with absent or rudimentary 5th middle phalanx 
• Disease spectrum with oculodengodigital dysplasia (ODDD)

SD4

• Haas Type 
• Very rare (4 cases reported in literature) 
• Complete bilateral soft-tissue syndactyly 
• Polydactyly with extra digit and metacarpal 
• Autosomal dominant inheritance

SD5

• Most common affects the 3rd and 4th digits or the 4th and 5th digits of the hand 
• Associated bony fusion of metacarpals 
• Autosomal dominant as well as X-linked recessive inheritance have been described

SD6

• "Mitten hand" deformity 
• Unilateral syndactyly of the 2nd to 5th digits 
• Limited research into genetic cause

 SD7

• Very rare phenotype characterized by Drs. Cenani and Lenz 
• Autosomal recessive inheritance reported 
• Fusion of metacarpals 
• "Disorganization" of phalangeal development 
• Severe shortening and fusion of ulna and radius

 SD8

• Characterized by bony fusion of the 4th and 5th metacarpals with syndactyly 
• X-linked recessive trait

 SD9

• Mesoaxial Synostotic Syndactyly (MSSD) 
• Complete syndactyly and synostosis of 3rd and 4th digits 
• Bony reduction in the proximal phalanges 
• Aplasia/hypoplasia of the middle phalanges of the 2nd and 5th digits 
• Soft-tissue syndactyly of the toes

Other Syndactylies

Acrosyndactyly

• Syndactyly associated with congenital construction bands
• No genetic basis

 Syndromic Syndactylies

• Extensive and growing list of syndromes
• Most common include Poland syndrome, and Acroencephalosyndactyly (Types I-V)

Poland Syndrome

Ipsilateral chest wall and upper extremity involvement with some of the following features:

• Hypoplasia/aplasia of the pectoralis muscle and other chest wall muscles
• Hypoplastic skin/subcutaneous tissue/breast
• Absent ribs and costal cartilage
• Shortened upper arm and forearm
• Simple, complete, or incomplete syndactyly

No definite cause has been identified with an estimated incidence of 1:30,000

Acroencephalosyndactyly

Craniosynostosis and syndactyly

• Type I: Apert syndrome (Mid face hypoplasia, foot and hand syndactyly)
• Type II: Carpenter syndrome (Acrocephaly, foot and hand syndactyly)
• Type III: Saethre-Chotzen syndrome (eyelid and cranial abnormalities, syndactyly of the 2nd and 3rd fingers)
• Type IV: Goodman syndrome (now classified with type II)
• Type V: Pfeiffer syndrome

Management

• Surgery is the mainstay of management
• Intervention is non-urgent, but age related targets exist for aesthetic and functional considerations
• Multiple digit involvement is surgically released in stages, with border digits released first
• Full thickness skin grafts and flaps used for soft tissue coverage

Polydactyly

• Presence of supernumerary digits
• Isolated or a syndromic feature
• Currently, over 221 syndromes associated with polydactyly
• Can be classified as ulnar, radial, and central polydactyly

Radial (preaxial) polydactyly

• Up to 1 in 3000 births
• Wassel classification (Type 1 to 7) most widely used
• Highest incidence of Type 4
• Usually isolated but Type 7 is associated with autosomal dominant inheritance
• Surgical management requires complicated reconstruction

Ulnar (postaxial) polydactyly

• Presentation varies from a well developed digit (type A) to a skin tag (type B) according to Temtamy and McKusick classification
• Up to 1 in 143 live births in African Americans, compared to 1 in 1339 live births in Caucasians
• Autosomal dominant inheritance for isolated presentation
• Autosomal recessive inheritance and syndromic association seen in Caucasian populations
• Can be treated with simple excision, or reconstruction in cases of joint involvement

Central Polydactyly

• Duplication of a non-border digit
• Rare form of polydactyly
• Most commonly seen in the ring finger and middle finger
• Most often presents as a part of synpolydactyly (SD2)