Donald S. Bae
DEFINITION
Syndactyly refers to the failure of separation between adjacent digits, resulting in “webbed” fingers.
Congenital syndactyly is classified according to the extent of digital involvement and the character of the conjoined tissue.
Complete syndactyly extends to the digital tips (FIG 1A), whereas incomplete syndactyly ends proximal to the fingertips (FIG 1B).
Simple syndactyly refers to digits connected only by skin and soft tissue. Complex syndactyly denotes bony fusions between adjacent phalanges.
Complicated syndactyly refers to the interposition of accessory phalanges or abnormal bones between digits.
ANATOMY
Understanding of normal digital web space anatomy guides surgical reconstructive efforts.
Typically, the index–long and ring–small finger commissures are U-shaped, whereas the long–ring web is V-shaped.
The non-glabrous skin of the normal web space is sloped about 45 degrees from proximal–dorsal to distal–volar, extending to roughly the midpoint of the proximal phalanx.
The natatory ligaments (or superficial transverse metacarpal ligament) help form the web contour and join adjacent lateral digital sheets.
Normally, each digit is vascularized in part via a radial and an ulnar digital artery, which arise from the bifurcation of the common digital arteries.
In simple syndactyly, adjacent digits are joined by varying amounts of skin and soft tissue.
The nail plates may or may not be fused.
The joints, ligaments, and tendons of the affected digits usually are normal.
It is of critical surgical importance that the bifurcation of the digital arteries and nerves may be abnormally distal in cases of syndactyly.
PATHOGENESIS
Syndactyly represents a failure of differentiation and is so classified by the embryologic classification of congenital anomalies adopted by the International Federation for Societies for Surgery of the Hand.
Embryologically, the digits arise from condensations of mesoderm within the rudimentary hand paddle of the developing upper limb.
During the 5th and 6th weeks of gestation, interdigital clefts form through the process of apoptosis, or programmed cell death, beginning at the digital tips and proceeding in a distalto-proximal direction.
The apical ectodermal ridge regulates this embryologic process, in conjunction with fibroblast growth factors, bone morphogenetic proteins, transforming growth factors, homeobox gene products, and the sonic hedgehog protein.
Interruption of this precise and highly regulated process results in syndactyly.
NATURAL HISTORY
There is no potential for spontaneous resolution.
Given the importance of independent digit function in today's world, surgical release is recommended for simple complete syndactyly, with few exceptions.
When digits of differing lengths are joined, the syndactyly may lead to deformity and growth disturbance, with the longer digit typically developing a flexion contracture and angular deviation toward the shorter digit.
Simple complete syndactyly of the long–ring interspace may be well tolerated and may not significantly compromise growth or function in young patients.
Simple incomplete syndactylies may be aesthetically subtle and cause little functional compromise. In these situations, observation may be considered.
PATIENT HISTORY AND PHYSICAL FINDINGS
The diagnosis of syndactyly usually is not subtle, and the extent of digital involvement typically is readily apparent.
Syndactyly is the most common congenital hand anomaly, with an estimated incidence of 1 in 2000 to 2500 live births.
The true incidence of syndactyly is unknown, in part because of the difficulty distinguishing mild simple syndactylies from normal web spaces.
FIG 1 • A. Simple incomplete syndactylies of the bilateral third web spaces, with the left hand more severely affected. B. Simple complete syndactyly of the second and third web spaces is seen in another patient. Observe the conjoined fingernail (synonychia) between the long and ring fingers. (Copyright © 2006 Children's Orthopaedic Surgery Foundation.)
The third web space is most commonly affected (50%), followed by the fourth (30%), second (15%), and first (5%) web spaces.
Males tend to be more commonly affected than females, and whites more than blacks or Asians.
Inheritance is thought to be autosomal dominant with incomplete penetrance and variable expression.
The absence of differential motion of the affected digits suggests a complex or complicated syndactyly.
Because the joints and tendons usually are normal, patients typically have flexion and extension creases over the interphalangeal joints and active digital motion.
Syndactyly may exist in isolation or may be seen in the context of associated clinical syndromes, including Poland syndrome, Apert syndrome, and constriction band syndrome. For this reason, careful evaluation of the entire upper extremity, contralateral upper limb, chest, and feet is advised.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Plain radiographs of the affected digits or hand are routinely obtained to accurately classify the syndactyly and assess for bony fusions or interposed or accessory bones (FIG 2).
MRI, angiography, or other diagnostic studies are not typically obtained, because they do not assist surgical decisionmaking or operative treatment.
NONOPERATIVE MANAGEMENT
Nonoperative management may be considered for mild, simple incomplete syndactyly.
Nonoperative treatment also may be favored in cases of complicated syndactyly with the so-called “superdigit” or in cases of complex polysyndactyly, because of the difficulty in achieving reproducible functional improvement with surgical release.
However, given the importance of independent digital motion—particularly in the current keyboard-driven digital age—nonoperative treatment of simple complete syndactyly is not recommended.
SURGICAL MANAGEMENT
General surgical principles include the following.
Digits of differing lengths should be released early to prevent deformity and growth disturbance of the affected digits.
Digits should be operated upon on only one side at the same time, to avoid vascular embarrassment.
Local skin flaps should be used to recreate the commissure to avoid scar contracture and “web creep.”
FIG 2 • A. AP radiograph of the patient depicted in Figure 1B. Note the simple complete syndactyly between the index and long fingers and a complex complete syndactyly between the long and ring fingers. B. AP radiograph depicting a complicated polysyndactyly in another patient.
Zigzag lateral flaps should be created to avoid longitudinal scar contracture.
Judicious defatting of the skin flaps should be performed to facilitate skin closure, reduce tension across the flaps, and improve the aesthetics of the reconstructed fingers.
Full-thickness skin grafts typically are used to cover “bare areas” after syndactyly release. (In cases of simple complete syndactyly, the combined circumference of the separated digits is 22% greater than the original circumference of the syndactylized digits.)7,9
Preoperative Planning
The timing of surgery must be considered in preoperative planning.
There is great variability in recommendations of when releases should be performed.
Flatt wrote, “I believe one should ask not how soon the operation can be done but rather how late the functional demands of the hand will allow postponement of surgery.”9
In general, releases are performed between 6 and 24 months of age.
As mentioned, digits of differing lengths (eg, thumb–index syndactyly) should be released earlier to avoid secondary deformity.
There is some evidence that releases performed after 18 months have better long-term outcomes with lower incidence of web creep.10,11
Positioning
The patient is positioned supine with the affected limb supported on a hand table.
Placement of a sterile or nonsterile tourniquet must be sufficiently proximal to allow access to the antecubital fossa, if full-thickness skin graft is to be taken from that site.
If the skin graft is to be harvested from the inguinal region, the ipsilateral groin is prepared and draped to allow for easy access.
Before draping, a surgical pen may be used to mark the inguinal skin fold when the hip is flexed; graft harvest along this axis will allow for a more aesthetic skin closure.
Care should be taken to harvest the skin graft lateral to the femoral artery to avoid transfer of hair-bearing skin.
Approach
The principles of separation for simple complete syndactyly are well accepted; however, there is tremendous variation in the surgical incisions and skin flap designs used for these operations.
All use local tissue to reconstruct the interdigital commissure, and all employ interdigitating zigzag lateral flaps. Dorsal skin flaps are preferred for commissure reconstruction, because of their pliability and ability to recreate the normal dorsal–proximal to volar–distal slope of the web.
When dorsal skin is used to create the commissure, the length of the dorsal flap should approximate two thirds of the length of the proximal phalanx to create an appropriate slope to the web. The proximal extent of the volar incision will become the new palmodigital crease (FIG 3A).
Furthermore, flaps are designed to interdigitate during closure; to achieve this, palmar triangular flaps are based at the level corresponding to the apex of the dorsal flaps. These flaps usually are fashioned to traverse between the midlines of the syndactylized digits.
FIGURE 3B shows examples of skin incisions for simple complete syndactyly releases.19
FIG 3 • A. Skin incision design. The dorsal skin flap measures approximately two thirds the length of the proximal phalanx, and the zigzag incisions are fashioned between the midlines of the syndactylized digits. B–I. Skin incisions used for release of simple complete syndactyly. B: Cronin, 1943. C: Flatt, 1962. D: Blauth, 1970. E: Hentz, 1977. F: Upton, 1984. G: Gilbert, 1986. H: Wood, 1998. I: James, 2005.
TECHNIQUES
RELEASE OF SIMPLE SYNDACTYLY
Release of Simple Complete Syndactyly Using Full-Thickness Skin Graft
After the tourniquet is inflated, the skin is incised, and hemostasis achieved with bipolar electrocautery (TECH FIG 1A,B).
Dorsal skin flaps are raised first, preserving the extensor paratenon.
Volar skin flaps are then raised, and neurovascular bundles are identified.
Digits are carefully separated distal-to-proximal, releasing the interdigital fascia that often connects the syndactylized digits (TECH FIG 1C). The transverse metacarpal ligament is not divided.
The bifurcation of the common digital artery and nerve is identified; if there is a distal bifurcation precluding restoration of the commissure with the dorsal skin flap, consideration may be given to splitting the fascicles of the common digital nerve or ligating one of the proper digital arteries.
For isolated syndactyly release, the smaller-caliber or nondominant artery may be taken.
If a syndactyly release is planned on the other side of one of the digits, its proper digital artery should be preserved.
Skin flaps are then defatted and allowed to interdigitate.
The dorsal skin flap is then advanced to the palmodigital crease and secured with multiple interrupted 5-0 absorbable sutures (eg, chromic or polyglactin; TECH FIG 1D).
Interdigitated skin flaps are similarly reapproximated with multiple interrupted 5-0 absorbable suture.
Skin defects are identified and covered with full-thickness skin graft, which may be harvested from the hypothenar eminence, antecubital fossa, or inguinal region (TECH FIG 1E).
The tourniquet is deflated, and vascularity of the digits and flaps is confirmed.
A non-adherent gauze bolstered with moist cotton is then placed into the newly formed web space, applying gentle compression to the skin graft sites.
Care should be taken to place the dressing deep within the commissure to avoid re-syndactylization during the healing process.
TECH FIG 1 • Dorsal (A) and volar (B) incisions for planned release of simple complete syndactyly of the long and ring fingers. C. The digits have been separated. D. The dorsal skin flap is sewn in to recreate the interdigital commissure. E. Completion of the release with full-thickness skin grafting. (Copyright 2006 Children's Orthopaedic Surgery Foundation.)
An above-elbow cast is then applied with the elbow in 90 degrees of flexion, with liberal use of casting material to protect the surgical dressing.
Reconstruction of the Paronychium
In cases of simple complete syndactyly, the nail plates of the involved digits are conjoined, a phenomenon known as synonychia.
Although division of the midportion of the nail plate is easily performed, care must be made to reconstitute the nail folds.
Ideally this is performed using local tissue from the digital pulp.2
Laterally based flaps are incorporated into the skin incisions, raised from the shared hyponychium at the digital tips (TECH FIG 2).
The length of the flaps should equal the length of the nail plate.
Once these flaps are raised and the digits separated, the flaps are easily rotated and reapproximated adjacent to the new nail plates, recreating a paronychial fold.
Alternative solutions, including the use of skin graft, thenar or hypothenar flaps, or free composite toe grafts, are more involved and may provide less pleasing aesthetic results.
Technique of “Graftless” Syndactyly Release
Simple complete syndactyly releases may also be performed without the need for full-thickness skin grafting.5,13
TECH FIG 2 • Schematic diagram depicting the incisions used to release a synoncychia, using local tissue to reconstitute the nail folds.
TECH FIG 3 • Schematic diagram depicting incisions used to perform “graftless” syndactyly releases. (A: From Sherif, 1998. B: From Niranjan and DeCarpentier, 1990, and Ekerot, 1996.)
In general, principles of syndactyly release mentioned earlier apply.
In “graftless” techniques, however, dorsal skin is raised from the dorsum of the hand and advanced to recreate the interdigital commissure. The resulting defect is closed primarily in the fashion of a V-Y advancement flap (TECH FIG 3).
Because proximal skin is used to recreate the web, more tissue is available to allow for primary closure of the digits following judicious defatting of the flaps, obviating the need for skin grafting.
The use of preoperative tissue expansion to avoid the need for skin grafting for syndactyly release has been proposed. Results have been unpredictable at best, however, and this approach currently is not widely accepted.
Local Skin Flaps for Simple Incomplete Syndactyly
In cases of simple incomplete syndactyly in which the web does not extend beyond the level of the proximal interphalangeal joint (ie, the length of the syndactyly does not exceed the desired depth of the reconstructed interdigital commissure), release may be performed using local skin flaps without the need for full-thickness skin grafting.
Multiple flap designs have been proposed, and, in general, all are variations of double opposing Z-plasties14,16 (TECH FIG 4).
In these situations, brief postoperative cast immobilization is recommended until skin flaps have healed.
TECH FIG 4 • Schematic diagram depicting incisions used to perform release of simple incomplete syndactyly.
POSTOPERATIVE CARE
Cast immobilization usually is discontinued after 2 to 4 weeks.
The wound is kept dry until the scabs desiccate and fall off.
Silicone gel sheets, elastomere, or scar molds may be used to minimize hypertrophic scar formation.
Formal occupational therapy for motion and strengthening is not typically required, because most children will use their hands quite readily with activities of daily living.
OUTCOMES
Very little has been published regarding long-term outcomes following surgical release of syndactyly.
Furthermore, interpretation of the available literature is difficult given the diversity of clinical presentations, surgical techniques, and methods of evaluation.
In general, syndactyly release can be expected to provide excellent independent digital function with acceptable aesthetic results when performed according to the principles outlined in this chapter.
Colville3 reported the results of 57 simple syndactyly releases performed over a 10-year period with minimum 2-year follow-up.
Two patients required reoperation for early graft failure, and three others demonstrated slight angular deformity due to scar contracture, but they did not require additional surgery.
D'Arcangelo et al4 published their results of 122 releases in 50 patients with minimum 8 years of follow-up.
Satisfactory functional and aesthetic results were seen in most patients, but eight patients demonstrated web creep and three patients developed scar contractures.
DeSmet et al6 reported their results of 50 syndactyly releases in 24 patients.
A normal or near-normal web was seen in 74% of cases, and cosmesis was deemed satisfactory in 64%.
In their review of 218 releases performed in 100 patients, Percival and Sykes15 noted that 42 patients required secondary surgery for web creep (22%) and contracture (26%).
Toledo and Ger18 published their results of 176 releases performed in 61 patients with average 14-year follow-up.
Secondary procedures were performed in 30% of patients with simple syndactylies.
The need for secondary surgery was associated with operations performed before the age of 18 months, the use of split-thickness skin grafts, and the presence of complex or complicated syndactyly.
COMPLICATIONS
With adherence to the principles presented in this chapter and meticulous surgical technique, the risk of complications may be minimized; however, up to one third of patients may require secondary procedures following simple complete syndactyly release.
Digital necrosis is the most serious potential complication of syndacytly release. Careful identification and preservation of the digital arteries—in addition to avoidance of surgical release of both the radial and ulnar sides of a single digit at the same time—is critical to avoid vascular embarrassment and digital loss.
Skin graft failure may result from hematoma formation beneath the graft or shear stresses imposed on the graft during the healing process.
This risk may be greater in younger patients, in whom appropriate graft tensioning is more difficult and in whom postoperative immobilization is a greater challenge.
If allowed to heal by secondary intention, subsequent hypertrophic scar formation may lead to suboptimal aesthetic and functional results.
Skin flap failure due to devascularization is less common but also may lead to scarring and secondary contracture.
Triangular skin flaps should be designed with tip angles greater than 45 degrees to prevent tip necrosis.
Careful defatting of the flaps and primary closure without excess tension, in addition to assessment of flap viability after tourniquet release, will further aid in preventing skin flap complications.
Contractures and angular deformity of the released digits may occur owing to linear scars on the radial or ulnar aspects of the fingers.
Use of zigzag incisions and interdigitating flap designs will minimize this risk.
Nail plate deformity is common after simple complete syndactyly release in the presence of a synonychia.
Although techniques of nailfold reconstruction using distal pulp tissue will optimize aesthetic results, patients and families should be counseled in advance regarding this common occurrence.
“Web creep” refers to the distal migration of the reconstructed interdigital commissure with continued growth and is a common occurrence following syndactyly release, with a variously reported incidence of between 7% and 60% of cases.
Some evidence suggests that the risk of web creep may be diminished if release is performed after 18 months of age.
Other factors that may contribute to web creep include inappropriate flap design for commissure reconstruction, the use of split-thickness rather than full-thickness skin grafts, skin graft loss, and creation of a transverse linear scar in the reconstituted web space.
In cases of clinically significant web creep, secondary releases may be required.
REFERENCES
· Aydin A, Ozden BC. Dorsal metacarpal island flap in syndactyly treatment. Ann Plast Surg 2004;52:43–48.
· Buck-Gramcko D. Congenital malformations: Syndactyly and related deformities. In: Nigst H, Buck-Gramcko D, Millesi H, et al, eds. Hand Surgery. New York: Thieme Medical Publishers, 1988:12.
· Colville J. Syndactyly correction. Br J Plast Surg 1989;42:12–16.
· D'Arcangelo M, Gilbert A, Pirrello R. Correction of syndactyly using a dorsal omega flap and two lateral and volar flaps. J Hand Surg Br 1996;21:320–324.
· D'Arcangelo M, Maffulli N. Tissue expanders in syndactyly: A review. Acta Chir Plast 1996;38:11–13.
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· Niranjan NS, DeCarpentier J. A new technique for the division of syndactyly. Eur J Plast Surg 1990;13:101–104.
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· Percival NJ, Sykes PJ. Syndactyly: a review of the factors which influence surgical treatment. J Hand Surg Br 1989;14:196–200.
· Shaw DT, Li CS, Richey DG, et al. Interdigital butterfly flap in the hand (the double-opposing z-plasty). J Bone Joint Surg Am 1973;55A: 1677–1679.
· Sherif MM. V-Y dorsal metacarpal flap: A new technique for the correction of syndactyly without skin graft. Plast Reconstr Surg 1998; 101:1861–1866.
· Toledo LC, Ger E. Evaluation of the operative treatment of syndactyly. J Hand Surg Am 1979;4A:556–564.
· Upton J. Congenital anomalies of the hand and forearm. In: McCarthy JG, May JW, Littler JW, eds. Plastic Surgery. Philadelphia: WB Saunders, 1990:5279–5309.