Simple and Complex Syndactyly

Syndactyly (Simple)

Essential Information
Syndactyly is a common hereditary digit malformation where adjacent fingers are webbed due to a failure to separate during limb development.  Syndactyly is classified as “simple syndactyly” when fingers are connected by skin and soft tissue, rather than via an osseous or cartilaginous union.
 
Etiology
  • Separation failure of developing phalanges during organogenesis
  • Webbing between digits fails to regress in a distal to proximal direction at 6-8 weeks gestation
  • Due to defects in cytokine mediated apoptosis of portions of apical ectodermal ridge
  • Proximal webbing occurs when apoptosis defects cause interdigital tissue to persist but not extend with digits as they continue to elongate
Genetics
  • Autosomal dominant pattern with variable expression or reduced penetrance
  • < >1 in every 2,000 - 3,000 births
  • Males affected twice as frequently as females
  • Bilateral in half of patients, may be symmetrical or asymmetrical 
Risk Factors
  • Maternal smoking, poor nutritional status, lower socioeconomic status, and increased meat and egg consumption during pregnancy
  • Associated conditions 
Clinical Evaluation:
History / Exam Findings
  • Physical examination must include entire affected upper limb, contralateral hand, chest wall, and feet to search for additional anatomical differences
  • Most common between ring and long fingers (40% to 50%)
  • Second most common between ring and small fingers (25% to 28%)
  • Least common between thumb and index finger (7% to 9%)
Imaging / Lab Studies
  • Plain radiographs of hand are taken to detect skeletal deformities, concealed extra digits, or articular deformities 
Classification Schemes
  • Simple Incomplete: Only soft tissue involvement, no bony connections.  No involvement of nailfold.
  • Simple Complete: Only soft tissue involvement, no bony connections. Fused along full length of digits including nailfold
  • < >: Osseous or cartilaginous unions between adjacent digits< >:  Abnormalities beyond simple side-to-side digit fusions (accessory phalanges, abnormal tendons, muscles, or nerves interposed within fused interspaces)Complicated syndactyly can also refer to syndactyly associated with syndromes 
Treatment:
  • Surgery via syndactyly release is indicated in most cases
  • Mild, incomplete syndactyly without functional impairment does not always require surgery
  • Various flaps with and without skin grafting have been described
  • Goal is to create a normal webspace to improve appearance and digit function
  • Timing of surgery is generally around 12 months of age. Surgery should be performed early enough to allow for normal growth, but late enough to avoid postoperative complications
Outcomes:
  • Prognosis
    • Release of simple syndactyly is often successful in improving appearance and independent digit function 
  • Potential Complications
    • Iatrogenic nerve or artery injury
    • Graft or flap failure
    • Web creep
    • Joint contractures
    • Nail deformities

 
References:
1. Braun TL, Trost JG, Pederson WC: Syndactyly Release. Semin Plast Surg 30:162-70, 2016
2. Dao KD, Shin AY, Billings A, Oberg KC, Wood VE: Surgical treatment of congenital syndactyly of the hand. J Am Acad Orthop Surg 12:39-48, 2004
3. Malik S: Syndactyly: phenotypes, genetics and current classification. Eur J Hum Genet 20:817-24, 2012
4. Tonkin MA: Failure of differentiation part I: Syndactyly. Hand Clin 25:171-93, 2009


 

Complex Syndactyly

Essential Information
Complex syndactyly is a hereditary malformation where adjacent fingers are connected via an osseous or cartilaginous union.
 
Etiology
  • Apical ectodermal ridge (AER) persists in inappropriate locations
  • Apoptotic cascade cannot be appropriately activated
  • Leads to abnormal induction of digital rays, complex syndactyly, and clefting
Genetics
  • Autosomal dominant pattern with variable expression or reduced penetrance
  • Sporadic
  • Common feature of more than 300 hereditary syndromic malformations
Incidence
  • 1 in every 2,000 - 3,000 births
  • Males affected twice as frequently as females
  • Bilateral in half of patients, may be symmetrical or asymmetrical
Risk Factors
  • Maternal smoking, poor nutritional status, lower socioeconomic status
  • Associated Syndromes such as:
    • Poland’s syndrome - associated with unilateral hypoplasia of sternal head of pectoralis major and upper extremity
    • Apert’s syndrome - complex syndactyly associated with craniosynostosis, hypertelorism, exophthalmos, and mild mental retardation
    • Acrosyndactyly - amniotic disruption sequence where interdigital clefts are present proximal to level of syndactyly
 
Clinical Evaluation:
History / Exam Findings
  • Thorough exam of bilateral upper limbs, chest wall, and feet to search for additional areas of syndactyly or evidence of associated syndromes
  • Most common between ring and long fingers (40% to 50%)
Imaging / Lab Studies
  • Plain radiographs of hand to assess extent of skeletal deformity
  • Magnetic resonance imaging (MRI) or ultrasound to determine flexor tendon and vascular anatomy 
Classification Schemes
  • Simple Incomplete: Soft tissue involvement only, no involvement of nailfold.
  • Simple Complete: Soft tissue involvement only, involvement of nailfold
  • Complex: Osseous or cartilaginous unions between adjacent digits
  • Complicated: Abnormalities beyond simple side-to-side digit fusions (accessory phalanges, abnormal tendons, muscles, or nerves interposed within fused interspaces)
Treatment:
  • Syndactyly release around age 12 months
  • Various flaps with and without skin grafting have been described
  • Surgery often performed in stages for multiple digit involvement to avoid vascular compromise
  • Goal is to produce a hand with as many independent and functioning digits as possible
  • Contraindications: Superdigits (two metacarpals supporting a single oversized digit or single metacarpal supporting two or more digits), complex masses that move as a unit
 
Outcomes:
  • Prognosis
    • Complex syndactyly associated with twice the number of reoperations as simple syndactyly
    • Increased web creep and worse finger motion compared to simple syndactyly
       
  • Potential Complications
    • Iatrogenic nerve or artery injury
    • Graft or flap failure
    • Web creep
    • Joint contractures
    • Nail deformities


References
1. Braun TL, Trost JG, Pederson WC: Syndactyly Release. Semin Plast Surg 30:162-70, 2016
2. Dao KD, Shin AY, Billings A, Oberg KC, Wood VE: Surgical treatment of congenital syndactyly of the hand. J Am Acad Orthop Surg 12:39-48, 2004
3. Goldfarb CA, Steffen JA, Stutz CM: Complex syndactyly: aesthetic and objective outcomes. J Hand Surg Am 37:2068-73, 2012
4. Malik S: Syndactyly: phenotypes, genetics and current classification. Eur J Hum Genet 20:817-24, 2012
5. Tonkin MA: Failure of differentiation part I: Syndactyly. Hand Clin 25:171-93, 2009
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