Syndactyly

Several genetic abnormalities have been associated with syndactyly.[6, 7, 8]  Approximately 10-40% of cases are familial with variable penetrance. Syndactyly may occur as part of a syndrome or as sporadic events that are nonhereditary and nonsyndromic. One report indicated that there is an association between syndactyly and smoking during pregnancy.[9]

Syndactyly is the most common congenital abnormality of the hand, with a rate of 1 per 2000-3000 births.[10, 11, 12, 13] The male-to-female ratio is 2:1.

Despite appearing relatively straightforward, syndactyly release is a complex operation requiring well-honed skills. If the procedure is properly performed, the rate of complications is low, and the results are extremely gratifying for the parents and beneficial to the patients in improving hand functionality and in providing normal-appearing hands and fingers.

Although many patients with syndactyly have been evaluated by multiple specialists and referred by their primary care pediatrician, the hand surgeon should also obtain a thorough antenatal, postnatal, and familial history. In addition to the hand being examined, the cranium, face, torso, and lower extremities should be examined for anomalies.

The hand evaluation should proceed systematically, as follows:

• Note and document the number of digits present, the level of web involvement, the length of the finger, and the appearance of the fingernails
• Often, photographing or drawing a picture of the hands during the initial visit is helpful
• Passively move the fingers to determine bony union; differential motion occurs only if no underlying bony union is present; fusions of the fingernails often are associated with bony union, and a broad fingernail also may indicate a hidden polydactyly
• The extent of anomaly of tendons and neurovascular structures reflects the complexity of the syndactyly; in a simple complete or a complex syndactyly involving only the distal phalanx, the underlying tendon and neurovascular structures are usually normal, but in an individual with brachysyndactyly or complicated syndactyly, the bifurcation of the nerves and digital vessels may be located more distally, or only one side may be present
• Always obtain radiographs to help identify any other anomalies (eg, bony synostosis, delta phalanx, or symphalangism)

Classification of syndactyly is based on the severity of the clinical presentation.

The mildest form is simple syndactyly, which refers to fingers joined only by soft tissue. In simple syndactyly, the third web space between the long finger and the ring finger is the area most commonly involved, followed by the fourth, second, and (rarely) first web spaces. Bilateral involvement is found in 50% of patients.

When the soft-tissue union is only partial and does not extend to the fingertips (see the first and second images below), the condition is referred to as incomplete simple syndactyly. When the soft-tissue union extends to the fingertip, the condition is referred to as complete simple syndactyly (see the third and fourth images below).

Complex syndactyly refers to fingers joined by bone or cartilaginous union, usually in a side-to-side fashion at the distal phalanges.

The most severe form is classified as complicated syndactyly, which refers to fingers joined by bony fusion in other than a side-to-side fashion. It can include bony abnormalities, such as extra, missing, or duplicated phalanges and abnormally shaped bones (eg, delta phalanges). (See the image below.) Abnormalities in the musculotendinous and neurovascular structures may also be present.

Syndactyly can be an isolated finding, or it can be found in association with other abnormalities, such as polydactyly, cleft hands, ring constrictions, or craniofacial syndromes.[4]

Apert syndrome is the best known of the craniofacial syndromes. Another syndrome that may develop is Poland syndrome, in which the pectoralis muscle abnormality is found in association with symbrachydactyly or other anomalies of the ipsilateral upper extremity.[14]  Constriction band syndrome can be associated with syndactyly, but the etiology of the syndactyly is different.

Apert syndrome

Apert syndrome, or acrocephalosyndactyly, is a rare anomaly, occurring in 1 per 160,000-200,000 live births.[15, 16, 17]  Besides the characteristic facial anomalies of Apert syndrome, it is also defined by the associated upper- and lower-limb anomalies. The anomalies in the hands are mirror images of each other and are characterized by the following four common features:

• Radial deviation of a short thumb as a result of an abnormally shaped proximal phalanx (ie, delta phalanx)
• Complex syndactyly of the index, long, and ring fingers
• Symbrachyphalangism of the central segments of the index, long, ring, and small fingers
• Simple syndactyly of the web space between the ring and small fingers

The web space between the thumb and the index finger is variable, and the extent of syndactyly at this web space serves as the basis for the classification of Apert syndactyly into three types, as follows.

Type I is the most common and the least severe of the three types. The thumb is foreshortened and associated with a radial clinodactyly as a result of a delta phalanx of the proximal phalanx. Although it is separate from the index finger, the first web space is shallow.

A complex syndactyly includes the index, long, and ring fingers because of osseous or cartilaginous union of the distal phalanges. Simple syndactyly of the small and ring fingers is present; this syndactyly may be complete or incomplete. The distal interphalangeal (DIP) joint of the small finger is well formed and functional. Type I hands are often referred to as spade hands. (See the images below.)

Type II is more severe and is characterized by a simple incomplete or complete syndactyly of the thumb with the index ray, without any osseous union. The thumbnail matrix remains separate from the index fingernail. The hand has a large, concave palm. The bony union of the distal phalanges of the index, long, and ring fingers are more extensive than in type I. The ring finger–small finger syndactyly remains simple but complete. Type II hands have been referred to as mitten hands or spoon hands (see the image below).

Type III is the most severe and, fortunately, least common form. A tight osseous or cartilaginous union is present between all five fingers. All five nailplates are conjoined, and they sometimes have longitudinal ridges, which indicate separate underlying distal phalanges. The thumb is indistinguishable from the index ray. The small finger, although joined by a common fingernail, does not have an osseous union at the distal phalanx and remains a simple but complete syndactyly. Usually, metacarpal synostosis of the small and ring finger rays is present.

Type III hands have been termed rosebud or hoof hands (see the first and second images below). Radiographs are difficult to obtain and interpret because of the overlap of osseous structures (see the third image below).[16]

As stated, the goal of treating complex syndactyly is the surgical release of the fingers to increase the functionality of the hand. The timing of surgery is critical because the child requires multiple operations for other abnormalities of the cranium, midface, and orbits associated with Apert syndrome.

Poland syndrome

Poland syndrome is a sporadic congenital anomaly characterized by the absence of the sternal head of the pectoralis major muscle, along with hypoplasia or aplasia of the breast or nipple, with deficiency of the subcutaneous fat and axillary hair. There can be associated abnormalities of the rib cage and the ipsilateral upper extremity. It was first described by Alfred Poland in 1841 as a medical student, when he reported the absence of the sternocostal portion of the pectoralis major during a cadaver dissection.

In the hand and fingers, anomalies include symphalangism, syndactyly with hypoplasia, brachydactyly, or aplasia of the fingers. Two variations of hand anomalies with syndactyly in patients with Poland syndrome can be seen in the images below.

Constriction band syndrome

The syndactyly found in constriction band syndrome (also known as amniotic band syndrome) is not the result of failure of differentiation during embryogenesis. In this condition, the fingers are already formed, and because of the injuries due to the constricting amniotic bands, the fingers heal together at the site of injury, causing postinjury syndactyly.[18]  The extent of involvement may be mild, with only a rudimentary small skin bridge connecting the two fingers (see the images below).

The extent of involvement may be more severe, with a complete soft-tissue fusion in association with amputated fingers (see the images below).

Occasionally, epithelialized sinuses or fistula tracts can be found usually proximal to the level of the syndactyly (see the images below). The finger distal to the constriction ring is usually atrophic, or it has been amputated in utero as a result of ischemia. These findings in the fingers may be isolated or associated with other constrictions on the proximal arm, leg, or face.

If the syndactyly is minimal, standard techniques and skin grafts may be used to release the syndactyly (see the image below).

If sinus tracts or fistulas exist within the syndactyly, these tracts can often be released to reveal epithelialized web spaces, which do not require skin grafts (see the image below). The markings made prior to the syndactyly then require modification.

Obtain radiographs of the hands to evaluate for any other bony anomalies, such as synostosis, delta phalanx, or symphalangism.

If the infant has no associated medical conditions, a formal preoperative evaluation by the anesthesia team usually is not necessary. However, should there be any congenital syndromes or associated medical conditions, patients should be scheduled for operative clearance with the preoperative evaluation service of the hospital where the surgery will be done. Generally, if there is no issue with postoperative monitoring, many of these cases can be handled as outpatient procedures.

In itself, a minor incomplete syndactyly is not an indication for surgery if the only issue is its incongruous appearance. However, a syndactyly that prevents full range of motion in the involved fingers warrants surgical release to increase functionality of the fingers.[5] (See the images below.) As with any operation, exceptions to the rule exist.

In cases of complex syndactyly where the conjoint fingers together are functional but individually hypoplastic, separation of the conjoint fingers may make the two individualized digits nonfunctional, because only one set of tendons and one neurovascular pedicle may be present. This possibility must be carefully considered in those few individuals who have complex syndactyly. Otherwise, most patients with syndactyly benefit from surgical release.

Syndactyly requires surgical intervention. Full-term infants can be scheduled for elective surgical procedures as early as 5 or 6 months of age. Surgery before this age can increase anesthetic risks. Prior to that time, there is generally no need for intervention if there are no problems. If there is an associated paronychia (see the image below), which can occur with complex syndactyly, the parents are given instructions to wash the child's hands thoroughly with soap and water and to apply a topical antibacterial solution or ointment. Oral antibiotics are given when indicated.

The timing of surgery is variable. However, if more fingers are involved and the syndactyly is more complex, release should be performed earlier. Early release can prevent the malrotation and angulation that develops from differential growth rates of the involved fingers.[19]

In persons with complex syndactyly, the author performs the first release of the border digits when the individual is approximately 6 months old. This approach is used because differential growth rates are observed, particularly between the small finger and the ring finger or between the thumb and the index finger. Prolonged syndactyly between these digits can cause permanent deformities.

If more than one syndactyly is present in the same hand, simultaneous surgical release can be performed, provided that only one side of the involved fingers is released. For example, in a four-finger syndactyly involving the index, long, ring, and small fingers, the index finger can be released from the long finger and the small finger from the ring finger, leaving a central syndactyly involving the long and ring fingers (see the images below). If both hands are involved, bilateral releases can be performed at one operative setting.

Whenever feasible, bilateral releases should be performed to reduce the number of operations and the associated risks. Postoperative bilateral immobilization of the upper extremities is well tolerated in the child who is younger than 18 months. The increasingly active child who is older than 18 months has a difficult time with bilateral immobilization. Therefore, in children older than 18 months, any procedures must be staged unilaterally. The remaining syndactyly between the long finger and ring finger can be released approximately 6 months later (see the images below). 

In an individual with isolated central syndactyly between the long finger and ring finger, the release need not be accomplished until the second year of life because of similar growth rates between the long finger and ring finger. It is preferable to complete all major reconstructions before a child reaches school age.

However, even if the child is older than the ideal age (which is usually before school age, for functional, developmental, and psychological reasons), it is not too late to release the central rays (long and ring fingers), because they have similar growth rates. For example, a 5° flexion contracture could eventually improve once the fingers are released. In children, unlike adults, persistent flexion contractures are rare.

The technical details of syndactyly release are similar to the release performed in infants. In older patients, splints are still applied but can be removed earlier, at about 7-10 days, because the patients are more compliant with activity and with dressing changes after the splint is removed.[20]

Preparation for surgery

The parents are instructed to bathe the patient on the morning of surgery, with particular instructions to wash the hands and the groin region where the skin graft will be harvested.

Operative details

With any initial syndactyly release, only one side of the finger should be operated on at any given time to prevent ischemic compromise to the finger should one of the digital vessels be absent or be injured. The surgical division is individually tailored in accordance with the complexity and location of the syndactyly.

Generally, the release is accomplished by dividing the fingers and resurfacing the surgical wound with a well-vascularized dorsal trapezoid-shaped flap, interdigitating fasciocutaneous flaps, and full-thickness skin grafts to resurface interdigital spaces (see the images below). The web is reconstructed with a well-vascularized dorsal fasciocutaneous flap.[21, 22]

This flap is inset with a sloping inclination in the dorsal-to-volar orientation, with the distal edge ending at the midlength of the proximal phalanx. If the fingernail is involved, it should be divided longitudinally. If the fingernails are broad, they should be reduced to normal size. After osteotomy, local fasciocutaneous flaps should be applied to any bony exposure for stable coverage. Occasionally, when the area of exposed bone is small, a full-thickness skin graft may suffice.

It is important that the local interdigitating flaps be designed well to minimize the need for skin grafts. The full-thickness skin grafts are applied to areas that remain uncovered by the fasciocutaneous flaps.

The parents should be informed that as a rule, skin grafts are needed for all cases except the most minor cases of incomplete simple syndactyly (eg, those located in the first web space between the thumb and the index finger). In the setting of incomplete simple syndactyly, various techniques (eg, a double-opposing Z-plasty or a four-flap Z-plasty) are available that may not require skin grafts[23]  (see the images below). Some have studied the application of graft-free techniques to complete simple syndactyly as well.[24, 25, 26]

Many variations and techniques have been devised for syndactyly release; Upton reviewed their descriptions and their history.[27] Regardless of the techniques used, the following general principles must be applied to achieve optimal results:

• Use loupe magnification (2.5× or greater)
• Use zigzag lines to distribute the lines of contraction; avoid straight lines
• Use well-vascularized flaps to reconstruct the web space
• Defatting of the interdigital space should be judicious; otherwise, the neurovascular pedicles may be injured
• Release only one side of a finger at a time during the initial syndactyly release, and whenever possible, perform bilateral syndactyly releases, particularly in children younger than 18 months, when bilateral surgical procedures are well tolerated
• Harvest full-thickness skin grafts from a hairless region that has a reasonable color match
• During dissection, a tourniquet is crucial for achieving a bloodless field so as to avoid damage to the neurovascular structures
• Achieve hemostasis in the wound base to optimize survival of the skin graft
• Use only absorbable sutures, such as 5-0 mild chromic catgut or synthetic rapidly absorbable sutures, which may cause less inflammation

In cases involving release of complex syndactyly, temporary external fixation may be useful in stabilizing the commissure and facilitating surgical wound care.[28]

Skin grafts

Full-thickness skin grafts are preferable to split-thickness skin grafts because the former are less likely to contract over time and because they usually grow with the patient. The most common full-thickness skin-graft donor site is the lateral inguinal region close to the anterior superior iliac crest. This area is generally hairless, even in the hirsute adult. The skin is taken as an ellipse, and the donor site is closed primarily. Morbidity associated with this donor site, particularly the infection rate, is low. The incision heals nicely and is usually inconspicuous (see the image below).

Because it may be necessary to harvest a large skin graft from this area, it is permissible to extend the donor site into the hair-bearing skin. It is important to thin the graft so as to decrease the chance of hair growth in the graft, which can occur during puberty. The parents should be advised that hair growth in the skin graft is a possibility, particularly in male patients.[29]

In complex syndactyly, such as Apert syndrome, in which a pedicled groin flap may be used later for resurfacing the interdigital space after the central syndactyly release, the surgeon may want to consider harvesting the full-thickness skin graft from the midline suprapubic region through a Pfannenstiel incision.

Nonpigmented skin can also be harvested from the plantar surface of the foot[30] or from the hypothenar region of the hand. In the nonambulating child, the plantar incision can be closed primarily and is well tolerated with minimal morbidity. Both hypothenar and plantar donor sites for the skin graft are limited in quantity and can therefore be used to resurface only small wounds.

Another source of skin, in an uncircumcised male, is the prepuce. This skin also tends to hyperpigment over time and may not be available if the patient has already been circumcised.

A well-molded bulky dressing is applied to the upper extremity. A generous amount of antibiotic ointment is directly applied to the skin graft, and the incisions are followed by a nonadherent dressing material such as Adaptik. (Because petroleum-impregnated cotton gauze products tend to dry quickly and can become adherent to the skin grafts with the first dressing change, the surgeon may want to avoid them.)

This step is followed by gently laying cotton fluffs within the web space. The upper extremity is then placed into a well-padded bulky long arm dressing, which is reinforced with a fiberglass long arm splint. The skin-graft donor site is closed with absorbable sutures and adhesive strips and covered with gauze and clear cellophane adhesive.[31]

The parents are instructed to remove the skin-graft donor site dressing on postoperative day 3. They may then start bathing the child and can get the donor site wet, with encouragement to wash this area with soap and water. The long arm splint is kept in place and is removed at 2 weeks. The utmost care should be taken when the dressing is removed. If there is any concern about the possibility of loss of the skin graft with an early dressing change at 2 weeks, the dressing is left in place for 3 weeks.

If any concern exists about the child being unable to tolerate a dressing change in the office, the dressing is removed intraoperatively, and the parents are directed to perform daily wound care. The parents change the dressing once a day for 2 weeks, gently washing their hands before each dressing change. During these changes, an antibiotic ointment is applied with a cotton swab to gently agitate any dried blood or residual drainage that is adhering to the sutures. The web spaces are dressed with 2 × 2 cotton gauze, laid into the web space to prevent scar adhesions and synechiae. This dressing is then reinforced with 2-in. (5-cm) gauze.

Stockinettes are then applied over the arms and secured to the patient's shirt at the shoulder with safety pins to prevent the patient from chewing or taking the dressing off. If the bandages stick to the sutures or to the wound, the parents are instructed to pour warm water with peroxide as needed to lift the dressing off atraumatically. The parents are instructed about scar management starting 6 weeks after surgery.

Complications of syndactyly release include the following[32] :

• Recurrence of syndactyly
• Finger ischemia
• Contracture
• Various skin-graft complications

Recurrence of syndactyly

Distal migration of the web (ie, web creep) can occur, even after successful release. The reported incidence has ranged from 7.5% to 60%.[10, 33, 34]

The causes are multifactorial. If recurrence appears early, it is usually the result of the presence of synechiae between the incision lines and, most likely, poor take of the skin graft. Because of this, making certain that the interdigital spaces remain separated is important in the early postoperative period.

Also, it is important to create a dorsal flap that is well vascularized at the tip, where it will be sutured to the base of the web. The flap is important in providing tissue that has skin elasticity that with adapt with the growth of the finger. Skin-graft loss also can contribute to web creep by increasing the possibility of scar contracture.

However, the major reason why web creep occurs is the discrepant growth rates between the scar and the surrounding tissue, leading to the appearance of an incomplete simple syndactyly. Depending on the severity of the web creep (see the image below), further release, as well as skin grafting, may be necessary. If this is left untreated, angulation and malrotation can occur.

The most common causes of a web not being deep enough are tip necrosis of the dorsal flap and skin-graft loss. In such cases, re-release and additional skin grafting are required. During adolescence, the web may migrate distally (ie, creep), in that the skin graft may not grow in a manner commensurate with the growth spurt of a patient. Release may be required if this complication interferes with function.

Finger ischemia

Although rare, finger ischemia can occur if a developmental anomaly with the digital vessels is present or if a digital vessel is damaged. This is why only one side of the finger should be operated on during initial syndactyly release.

Contracture

Occasionally, despite the surgeon's best effort and the creation of well-planned flaps, a contracture develops along the length of the incision line. This can result in a scar contracture and angulation of the finger. To prevent further angulation, a Z-plasty or skin graft will be needed to release this contracture (see the images below).

Scar contractures often develop in the web space within the first 6 months, making the webs more shallow, even if no skin-graft loss has occurred and the flaps have been correctly designed. The author usually recommends that the parents massage the webs to help with scar remodeling. Parents are also encouraged to place elastic bandages (eg, Coban bandages) in the webs to stretch them. The judicious use of steroid creams can also help with tight scars.

Skin-graft complications

Partial skin-graft loss results in an open wound that heals by secondary intention. As in any wound that heals by secondary intention, the contracture forces are considerable. The deforming forces can be so great that they produce angulation of the fingers, which requires further corrective surgery. Obtaining complete hemostasis in the wound base before the application of the skin graft is extremely important, as is securely sewing the skin graft. Proper postoperative dressings are also important to the success of the skin graft.

Because of the zigzag incisions and the need for skin grafts, the finger has a patchwork appearance. In a light-colored individual, this difference is not noticeable. However, in a patient who has medium-to-dark pigmentation, spears or islands of pigmented skin in the usually nonpigmented palmar surface can be the result (see the images below).[35] To avoid this effect, nonpigmented skin grafts may be harvested from either the plantar surfaces of the feet or the hypothenar regions of the hands.

Usually, the lateral groin or inguinal region is hairless, particularly in females. Because the full-thickness skin is harvested at a young age, before the child has developed secondary hair growth, the skin grafts may start producing hair at puberty. This occurs more often in male patients. Inform the parents and patient of this possibility. If hair growth occurs, the hair may be trimmed, or the patient can undergo depilatory treatment.

Occasionally, if the problematic skin graft is small and if laxity is present in the surrounding native skin, the skin graft can be excised directly and the wound closed primarily. Alternatively, the patient may be offered a repeat skin-graft procedure with skin obtained from a part of the body that does not produce hair.

US complications data

McQuillan et al analysed data from the National Surgical Quality Improvement Program (NSQIP) to assess the incidence of acute complications within 30 days of surgery for congenital hand differences (including simple syndactyly, complex syndactyly, and polydactyly).[36]  In the 1656  cases, the overall incidence of complications was 2.2%; the most common of these was superficial surgical-site infection (SSI; 1.7%), followed by related readmission (0.3%). The incidence of complications was higher in patients undergoing complex syndactyly repair (5.2% vs 2.3% for all others).

Canizares et al used the Pediatric Health Information System (PHIS) database to characterize complications and cost associated with syndactyly surgery in 38 US pediatric hospitals.[37] In the 2047 patients identified, the postoperative complication rate was 1.9%, with a postoperative infection rate of 1.6% and a surgical complication rate of 0.3%. The median adjusted standardized cost was $4112.50. Patients with more than one diagnosis had a 19 times higher risk of complications than those with a single diagnosis of syndactyly, and their hospital costs were 13% higher.

Chouairi et al used data from the NSQIP Pediatric database to assess 956 syndactyly cases, evaluating patient demographics, surgical factors, perioperative outcomes, and risk factors.[38] Patients of plastic surgeons had significantly more airway abnormalities and shorter operating times than those of orthopedic surgeons. Patients with complex syndactyly had significantly more ventilator dependence, tracheostomy, and comorbidities than those with simple syndactyly, as well as longer operating times and a higher rate of superficial SSI. Overall, syndactyly repair was found to be a safe procedure with few major or minor reconstructive complications, regardless of surgical specialty or syndactyly type.

At the time of the first dressing change, the skin graft has become adherent, and the child may start to use his or her fingers as tolerated, although the parents are instructed to place a stockinette over the arm to prevent the child from inadvertently contaminating and injuring the site.

The author usually waits for 6 months before performing the next syndactyly release or revision.