SYNDACTYLY

Introduction

Syndactyly is a congenital anomaly whereby adjacent digits are webbed together because they fail to differentiate during development. Syndactyly and polydactyly (extra digits) are the most common hereditary limb malformations. Syndactyly can be complete, meaning that the inter-connection extends the full length of the digits, or incomplete, which describes an inter-connection that is less than complete. In simple syndactyly, the connection is formed by skin and/or fibrous tissue. In complex syndactyly, the connection involves bone and can be complicated by variations of the musculotendinous and neurovascular structures. Most of the well-characterized phenotypes are inherited as an autosomal dominant type; however, autosomal recessive and X-linked recessive types have also been described.  Thge autosomal dominant pattern of inheritance is linked to the 2q34-q36 gene.  The portiion of the embryogenesis that affacts the hand is between the 4th and 8th weeks of development.  The hand paddle is initially covered by apical epidermal ridge (AER).  If the AER fails to fragment, i.e. failure of didefferetniation occurs, then syndactyly of the digits can result.3. The most common syndactyly is a simple syndactyly between the long and ring fingers.  The next most common is between the fourth and fifth digits, then syndactyly between the thumb and index finger.1-4

Incidence and Related Conditions1-4

  • Estimated incidence: 2-3 in 10,000 live births; twice as common among males
  • ~50% of cases are bilaterally symmetrical
  • ~80% of cases are sporadic
  • Associated conditions include Apert’s syndrome, Poland’s syndrome, congenital constriction bands, ectodermal dysplasia, focal dermal hyoplasia, oculodigital and orodigital anomalies, hemangioma, giantism

Syndactyly is typically classified using the following 5 types:1-4

  • Incomplete: webbing or connection between adjacent digits and does not extend to the fingertips
  • Complete: webbing extends all the way up the fingertips
  • Simple: fingers are joined only by skin and soft tissue
  • Complex: fingers are joined by bone or bony cartilage and soft tissue in a side-by-side manner
  • Complicated: fingers are joined by bone or bony cartilage and soft tissue in a manner that is not just side-by-side.  The adjacent digits maybe on top of or beneath each other etc.

Anatomic Pathology

  • Insufficient amount of skin (Note: the circumference of two separate digits added together is greater than the circumference of two digits together- see video below.)
  • Insufficient vascular supply caused by an abnormal number of digital arteries and digital nerves. For example, there may only be one neurovascular bundle between the two connected digits.
  • Excess fascial interconnections
  • Fascial structures can be hypertrophied, displaced, or tight
  • Musculotendinous units have no dynamic capability due to marked hypoplasia or fibrosis
  • Bone anomalies 
  • Joints may be ankylosed, deviated, deformed, tethered, stiff or unstable

Rlated Anatomy

  • Skin - web shape, slope angle and position
  • Bone - phalanges
  • Fingernail(s)
  • Flexor and extensor tendons
  • Neurovascular bundles

Differential Diagnosis

  • Apert syndrome
  • Symbrachydactyly
  • Acrosyndactyly
  • Pseudosyndactyly
  • Brachysyndactyly
  • Ectrodactyly
  • Constriction band syndrome
Clinical Presentation Photos and Related Diagrams
Clinical Examples of Syndactyly
  • Classic Simple Syndactyly of left long and ring fingers.
    Classic Simple Syndactyly of left long and ring fingers. (Hover over right edge to see more images)
  • Palm view of classic Simple Syndactyly of left long and ring fingers.
    Palm view of classic Simple Syndactyly of left long and ring fingers.
Pathoanatomy Photos and Related Diagrams
Anatomy of Syndactyly
  • Note the normal slope of the web goes distally last at approximately  45 degree angle.  The slope starts dorsal proximally (1) and goes volubly distally(2)
    Note the normal slope of the web goes distally at approximately a 45 degree angle. The slope starts dorsal proximally (1) and goes volarly distally(2)
Symptoms
Child can not used the involved digits independently
Difficulty with activities of daily living
Poor (abnormal) cosmetic appearance
Typical History

A two year old male infant was brought for evaluation because of bilateral webbing between the long and ring fingers.  The connection extended from the hand to the finger tips and included a merged fingernail.  The connected fingers were beginning to interfer with the development of finger and hand dexterity. The family history was positive.  The parents wanted surgical reconstruction but expressed concern about the need for general anesthesia and the risks of surgery.

Positive Tests, Exams or Signs
Work-up Options
Images (X-Ray, MRI, etc.)
Syndactyly X-rays
  • X-ray of right III-IV complete simple syndactyly
    X-ray of right III-IV complete simple syndactyly. (Hover over right edge to see more images)
  • X-ray of left II-III partial  simple syndactyly
    X-ray of left II-III partial simple syndactyly
  • X-ray of right III-IV-V complex (arrows) syndactyly
    X-ray of right III-IV-V complex (arrows) syndactyly
  • X-ray AP and Lateral views of complex Apert's Syndactyly
    X-ray AP and Lateral views of complex Apert's Syndactyly
Treatment Options
Treatment Goals: 
  • Separate the webbed digits 
  • Improve independent digital function
  • Improve hand and digit appearance
Conservative: 
  • None
Operative: 
  • Age
    • Typical release: ages 9-18 mo
    • If tethering of digits: earlier release may be required
    • With border digits (thumb/index syndactyly or ring/little finger syndactyly) consider early releases because the shorter digits can tether the long digits thus interferring with growth and development.
    • Bilateral: aged <14-24 months
  • Procedure1-4
    • There are numerous techniques for separating webbed fingers.  Most include:
      • Doral flap, palmar flap or a combination
      • Zig-zag incisions on the fingers
  •  To avoid vascular insufficiency, only one side of a digit should be operated on at a time
  • For multiple syndactyly, operate on border digits first
  • Typically skin grafts are needed on the sides of the proximal phalanges.  Some surgeons attempt to preserve skin on radial side of involved digits to maximize pinch sensation and to save full-thickness skin graft for the ulnar side of the affected digit but this is difficult to do.
  • Butterfly flap with skin graft can be useful when dealing with web creep that needs correction or for short partial syndactyly
Hand Therapy
  • Wound care and dressing changes
  • Silicone sheets for hypertrophic scars
  • Night web splnts to keep web open
  • Massage
Complications
  • Overall complications related to surgical treatemt of syndactyly is very low.  One study that looked at complications for syndactyly and polydactyly surgeries together showed an overall complication rate of only 2.2%. Overall complications include readmission rates after the primary procedures and late revision surgeries.1-6
  • Acute Surgical Complications:
    • Superficial wound infections
    • Skin graft loss (5%)
    • Skin flap loss
    • Circulatory deficiency
    • Complete loss of a digit is extremely rare and associated with complex and complicated cases
  • Chronic Surgical Complications:
    • Web creep which is difficult to measure and reported with marked variabilty: one report cited rate of 3-22% and another cited a rate of 7-60%.  Creep of the web is specially a problem with split thickness skin grafts.5,6
    • Hypertrophic scars
    • Scar contracture of digit(s)
    • Fingernail deformity (Very common and difficult to avoid)
Outcomes

Generally, no surgical treatment is required after hand reconstruction is completed but parents should be warned to return if recurrent deformity develops with growth. Examples include web creep, scar complications etc.

Video
Syndactyly and Finger Circumference
Key Educational Points
  • When the complete syndactyly includes a single wide fingernail (synonychia), nail fold reconstruction will be needed but none of the available techniques will consistently reproduces normal looking nail folds on each side of the release.
  • Warn parents that the incisions will look awful at first dressing change. And that making perfectly normal looking hands is not possible.
  • Warn parents that additional surgery may be needed with growth especially in complex and/or complex syndactyly reconstructions.  
  • Assess web and digital flaps with the tourniquet deflated.  Sometimes a few sutures will have to be loosened and/or careful defatting done to assure adequate circulation to the digits.
  • Syndactyly release timing:  Get surgical reconstruction done before age two and do border digits earlier.
  • If three digits are in a combined syndactyly, reconstruction should be staged so that only one side of any digit is exposed to surgical trauma at one stage. (Don’t operate on two sides of the same digit at the same procedure.)
  • Despite successful attempts to do syndactyly release without skin grafts, many experts feel grafting is always required.  
  • Avoid skin grafting in the commissure part of the web.  Use flaps to reconstruct the web and commissure.  Most surgeons prefer dorsally based flaps. The dorsal flap should go 2/3 the way to the dorsal PIP crease.
  • On the digit,  each dorsal triangular flaps should be the mirror image of the volar flaps.
  • When raising flaps dorsally, leave veins with the finger.  Volarly, identify and protect the neurovascular bundles.
  • Placing the web slightly deeper than normal allows for some distal web creep as the child grows.  To bring the flap proximally towards the MP joint, the junction of digital nerves can be separate in the distal common digital nerve with microsurgical technique to open the internal epineural interval between the connected two digital nerves. Removing the digital artery as a block to placing the flap more proximally requires ligating one digital artery in the web.  The surgeon must be certain that the one remaining digital artery will support the released finger.  When multiple digits are syndactylized together, use care to avoid ligating both vessels supplying a single digit.  You may have to use micro clamps temporarily with tourniquet deflated to adequately sasses the vascular supply of each digit.  
  • Small partial syndactyly or partial recurrence secondary to web creep can be treated by double Z-plasties which is better known as the butterfly flap.
Practice and CME
References

New Articles

  1. Sakamoto N, Matsumura H, Komiya T, et al. Syndactyly correction using a venous flap with the plantar cutaneous venous arch. Ann Plast Surg 2014;72(6):643-8. PMID: 24841825
  2. Landi A, Garagnani L, Leti Acciaro A, et al. Hyaluronic acid scaffold for skin defects in congenital syndactyly release surgery: a novel technique based on the regenerative model. J Hand Surg Eur 2014 ePub. PMID: 24664163
  3. Kozin SH.  Syndactyly.  J Hand Surg Am. 2001; 1(1):1-13.
  4. Niranjan NS, DeCarpentier J.  A new technique for the division of syndactyly.  Eur J Plastic Surg 1990; 13:101-104.
  5. McQuillan TJ, Hawkins JE, Ladd AL.  Incidence of acute complications following surgery for syndactyly and polydactyly: an analysis of the national surgical quality improvement program database from 2012 to 2014.  J Hand Surg Am. 2017; 42(9):749.e1-e7.
  6. Sullivan MA, Adkinson JM.  A systemic review and comparison of outcomes following simple syndactyly reconstruction with skin grafts or a dorsal metacarpal advancement flap.  J Hand Surg Am. 2017; 42(1):34-40.

Reviews

  1. Kvernmo HD, Haugstvedt JR. Treatment of congenital syndactyly of the fingers. Tidsskr Nor Laegeforen2013;133(15):1591-5. PMID: 23970273
  2. Malik S. Syndactyly: phenotypes, genetics and current classification. Eur J Hum Genet 2012;20(8):817-24. PMID: 22333904

Classic Articles

  1. Bauer TB, Tondra JM, Trusler HM. Technical modification in repair of syndactylism. Plast Reconstr Surg1956;17:385-91. PMID: 13335516
  2. Cronin, TD. Syndactylism: results of zig-zig incision to prevent postoperative contracture. Plast Reconstr Surg1956;18:460-8. PMID: 13408118
  3. Kozin SH.  Syndactyly.  J Hand Surg Am. 2001; 1(1):1-13.