Syndactyly

Overview

Syndactyly refers to the joining of fingers or toes. Syndactyly is one of the most frequent congenital extremity defects. In most situations, the digits are simply linked side by side by skin or other soft tissue that may appear webbed. Fingernails and toes can also be linked. To avoid the morbidity associated with this disorder, it must be detected and treated as soon as possible.

What is syndactyly?

The soft tissue and/or osseous fusion of neighboring digits in either the upper or lower extremities is referred to as syndactyly. Depending on the magnitude of the aberration, this causes "webbed" or "super" digits to appear. The presence (complex) or absence (simple) of bone fusion determines whether syndactyly is simple or complex. With the addition of the nail folds, complete syndactyly reaches to the tip of the digit, whereas partial syndactyly does not extend the whole length of the digit. The presence of interposed accessory phalanges or aberrant bones characterizes complicated syndactyly.

The most common placement is between the second and third toes on the foot and the long and ring finger on the hand. Syndactyly is most commonly seen as an independent condition after autosomal dominant inheritance with partial penetrance, but it is also linked to a number of genetic disorders, including Apert and Poland syndrome. Syndactyly is tolerated easier in the feet than in the hand, where separate digital motion is required. With the exception of minor instances, surgical digit separation is frequently recommended to improve hand function.

It is possible to unite two, three, four, or all five digits on a hand or foot. The united segment may extend just partially from the base of the fingers or toes to the tip (partial or incomplete syndactyly) or completely from the base to the tip (complete syndactyly).

What causes syndactyly?

A baby's hands develop in the shape of a paddle during pregnancy and then divide into individual fingers. This occurs extremely early in pregnancy, between the sixth and eighth weeks. If two or more fingers do not separate at this period, syndactyly occurs.

Syndactyly frequently runs in families. Children with syndactyly inherit the disorder from one or both parents. The disorder is sometimes part of a hereditary syndrome, such as Poland syndrome or Apert syndrome.

Symptoms of Syndactyly

Any child who presents with syndactyly should have a thorough history and physical exam. Any syndactyly in the family should be documented. Syndactyly may "skip" a generation as a result of incomplete penetrance. It is critical to determine whether there were any pregnancy or delivery issues. A complete neonatal orthopedic exam should be considered for patients who present as neonates or babies to look for any signs of an underlying condition. It should be noted that isolated simple syndactyly is not usually linked with a hereditary condition.

Other tests, including as hip dysplasia testing, infantile reflexes, metatarsus adducts, sacral dimpling, and spine examination, should be performed on every newborn or infant coming for assessment. If there are physical exam signs suggestive of an undetected hereditary condition, or if the syndactyly is severe or complex, a referral to a geneticist is recommended.

With particular emphasis to the syndactyly deformity, which digits are afflicted, and whether the affected digits appear to be fused by soft tissue exclusively or a mix of bone and soft tissue fusion, should be noted. It is important to observe the distal extent of the interdigital link. A physical examination of the fingers in the sagittal plane is helpful if there is a concern of subtle incomplete syndactyly. The web gaps are normally oriented at or near 45 degrees, with one of the afflicted fingers stretched and the neighboring digit flexed.

The existence of flexion and extension creases in the afflicted digits should be investigated since they can provide information about the underlying bone fusion and digit function. The examiner should evaluate the afflicted digits' ability to exhibit independent motion. Complex or sophisticated syndactyly becomes more likely if independent mobility of the digits is not exhibited.

The length disparities between the afflicted digits should be examined and recorded. The tester should inspect both hands and feet to confirm there are no further regions of syndactyly or supplementary digits. Finally, it is critical to inform the patient and family that there is a 30% skin deficit around the afflicted fingers on average. As a result, if the afflicted digits are separated, skin grafting may be recommended for a tension-free closure.

Because some patients may have previously received therapy or surgery, the history should include previous records and surgical reports. Photographs taken before to surgery or showing the evolution of creep after surgery may be beneficial. To assist plan future incisions, the skin should be checked for prior scars and skin donation locations. A complete sensory and vascular examination should be undertaken, especially in a review situation.

Diagnosing Syndactyly

Following an assessment of the patient's extremities, multiplanar radiographs of the afflicted hand or foot are recommended. X-rays are used to check for phalangeal and/or metacarpal osseous fusion. It is also useful in determining whether there are any supernumerary digits that were missed during physical examination. The abnormality can be diagnosed after a physical examination and imaging. Classification can be descriptive, such as incomplete or full (including the entire length of the digit), simple or complex (existence of bony fusion), and/or complicated (presence of accessory phalanges or abnormal bones). Tentamy and McKusick classification is another often used classification:

• Type I: Most commonly, the long and ring fingers in the upper extremities or the second and third toes in the lower extremity are involved. It is autosomal dominant with incomplete penetrance.
• Type II: Synpolydactyly including the long and ring fingers in the upper extremity and/or the fourth and fifth toes in the lower limb, as well as an accessory digit in the syndactyly web.
• Type III: Syndactyly involving in the ring and small finger. 
• Type IV: Complete syndactyly of all fingers
• Type V: Ring and little finger metacarpal or metatarsal fusions in the upper extremity, and third and fourth toes in the lower extremities.

In most situations of uncomplicated syndactyly, advanced imaging is not required. In situations of intricate and/or sophisticated syndactyly, MRI imaging may be helpful in determining the position of flexor tendons and neurovascular systems prior to scheduled surgery.

Treating Syndactyly

Syndactyly can be treated surgically or nonsurgically. Simple syndactyly of the toes is usually treated non-operatively if it does not interfere with function. Surgery for isolated syndactyly of the toes in this situation is for aesthetic purposes solely and should be undertaken only after a comprehensive discussion of risks with the patient and family. Incomplete simple syndactyly and webs linked with superdigits are two further reasons to choose nonoperative therapy. Superdigits are divided into two types:

Type I consists of two metacarpals that support one large digit, whereas type II consists of a single metacarpal that supports numerous digits. Surgery to separate these fingers is frequently ineffective, with disappointing outcomes. Complex synpolydactyly, in which the hand operates as a unit, and hands with no active muscle control are also contraindications to surgical therapy. Nonoperative therapy is sought if the surgeon believes that surgery will not enhance the function of the damaged hand/foot.

Syndactyly is commonly managed through operational management to provide a better functioning hand (or foot). If operational treatment for syndactyly is indicated, the scheduling of the procedure must be discussed. Syndactyly releases are often done between the ages of 12 and 18 months. Delaying surgery until the kid is at least 18 months old minimizes the risk of scar contracture and webspace creep as the youngster develops.

However, border digit syndactyly (short finger and thumb webspace) and numerous fusions should induce earlier release since the smaller digit tethers the longer digit as the patient develops. Release happens about 6 months of life to minimize angulation, rotary, or shortening of the next finger while also allowing for early grip and coordination development.

• Surgical Release

Depending on the intricacy of the implicated digits, the surgical release of syndactyly has several complexities. With this in mind, we will go over simple full syndactyly and then detail adjustments when additional complexities arise. It is critical to emphasize that loupe magnification or the use of an intraoperative microscope is required for a satisfactory outcome and to reduce the risk of neurovascular problems.

Achieving the best surgical result for patients with syndactyly is a multifaceted process with several aims. Among the objectives are

1. Creating new paronychial nail folds,
2. Developing the interdigital commissure (skin) of the digits to be separated, and 
3. Creating a new webspace.

There have been several ways published to separate the fingers, but the most well-known is Cronin's dorsal and volar zig-zag incision.

The zig-zag technique to the commissure allows for the creation of triangular-based flaps to aid with finger coverage. Incision planning should begin distally at the fingers, where the paronychial fold is planned. The conventional approach for developing these folds comprises laterally based triangular flaps that, once released, are sutured into the relevant finger, resulting in the formation of a new nail fold.

The dorsal and palmar incisions are then zig-zagged proximally to form the previously mentioned triangle flaps. It is critical to design the flaps such that the dorsal and volar flaps do not interdigitate with one other. The anticipated height of the webspace is decided as the incision is planned distally.

Once decided, a dorsal rectangular flap with a volar triangular base is often sketched. After the incisions are made, the case proceeds distally, beginning with the paronychial folds and progressing to the dorsal incision. As you proceed with your dissection, it is critical to make full-thickness flaps. To locate the neurovascular bundles, careful dissection is performed.

These typically bifurcate proximally, however occurrences of more distant bifurcation have been reported. If a distant bifurcation is found, each neurovascular bundle must be meticulously dissected so that it may be integrated into the correct digit. When the dorsal dissection is finished, the attention may be transferred volar and the separation accomplished. Following that, a tension-free closure is accomplished. If tension-free closure cannot effectively seal any sections of skin, full-thickness skin grafts from the hypothenar eminence, instep of the foot, wrist, cubital fossa, or groin can be acquired to replace the deficiencies.

It is critical to take a skin transplant from a region with a lack of hair development, since this might result in an unfavorable aesthetic effect. Split-thickness grafts should be avoided since they are known to contract up to 50% and provide an unfavorable post-operative outcome.

Other situations to examine are partial syndactyly, multiple digit syndactyly, and complicated syndactyly. Multiple flaps might be regarded in incomplete syndactyly. The length of the fusion of the damaged digits determines the objective of surgery for incomplete syndactyly. If just one-third of the digit length is damaged, a dorsal rectangular flap with volar-based triangular flaps can be used to successfully reconstruct the webspace.

To restore the webspace, a modified double reverse z-plasty has also been reported. The aim is to minimize the length of the webspace by a factor of one when compared to its width. A four flap z-plasty or central V-Y advancement with laterally based z-plasty has been documented in cases of syndactyly affecting the thumb. When numerous digits are involved, the surgeon must release the patient's syndactyly in stages.

Performing a syndactyly release on both the radial and ulnar sides of the finger at the same time may result in vascular compromise of the digit. In this instance, it is advised that the patient's surgery be conducted in phases. For example, if all of the digits in the hand except the thumb are involved, the initial stage of surgery might comprise the release of the index finger's ulnar border and the little finger's radial border. A second stage, usually done 6 months later, involves separating the ring and long finger.

Finally, when there is bone fusion (complicated syndactyly), extra surgical measures are necessary. Preoperative planning is crucial for separating fused phalanges. Synostosis separation should be designed to preserve as much normal anatomy as feasible. Closed wedge osteotomies may be recommended in difficult instances to adjust for angulation discrepancies.

The integrity of the collateral ligaments should be assessed intraoperatively to determine whether advancement or reconstruction is required. In circumstances of sophisticated and severe syndactyly, amputation of a nonfunctional ray may result in a better functional hand than repair and should be examined on a case-by-case basis by the surgeon.

Postoperative and Rehabilitation Care

Depending on the intricacy of the surgical operation, physician choice, and patient characteristics that may impact compliance with post-operative care, patients are often put in a bulky soft dressing, splint, or cast. Dressings are normally removed after two weeks. After the incisions have healed, the patient begins active range of motion exercises and scar massage. Hand therapy can be beneficial in aiding the patient with scar massaging methods and gaining range of motion. In the developing patient, it is critical to have ongoing follow-up to check for web creep issues. 

Syndactyly in children

This is a pretty frequent ailment. It occurs in around 1 in 2,000 to 1 in 3,000 infants. Some families have handed it along (inherited). Because of mutations in their DNA, it frequently affects only one individual in a family. About half of all newborns born with syndactyly only have one hand or foot. Half of the people have it on both hands or feet.

When a baby's hands and feet develop, they resemble mittens or paddles. The fingers and toes then separate. The fingers or toes did not split completely in most newborns with syndactyly. Fingers and toes of newborns with amniotic band syndrome may have split and then rejoined when they recovered following damage (acrosyndactyly).

Many newborns with syndactyly have no other physical defects and no health issues. However, this issue can occur in conjunction with other hand or foot disorders, such as polydactyly (also known as polysyndactyly), or with other hereditary illnesses or syndromes, such as Apert syndrome.

Prognosis

The prognosis is determined on the treatment technique and the intricacy of the syndactyly. Complex and severe syndactyly have poorer results and may necessitate multiple surgical operations. Great short- and long-term results have been observed in the case of uncomplicated syndactyly. However, it has been estimated that up to 10% of children who have syndactyly surgery would require revision surgery in the future.

Complications

An infection can arise during any surgical treatment. Although infection is a very uncommon consequence of syndactyly surgery, it has the potential to be fatal if it is not identified and treated immediately with surgical debridement or antibiotics. According to recent research, the rate of postoperative infection is 1.6 %. Patients with syndromic presentations and various preoperative medical diagnoses are more likely to have surgical complications. Scar development and contracture are another possible consequence.

This can be related to the use of split-thickness skin grafts or bone development in the surrounding area. Because full-thickness grafts are less likely to cause contracture, they are preferable when possible. Web creep is another prevalent difficulty. Web creep is defined as the distal migration of webspace as the patient ages. This can result in a progressive hand malformation.

In terms of web creep, the patient's age at the time of surgery may be a relevant determinant. To discover this problem at an early stage, the patient should be monitored at frequent intervals following surgery. Finally, digit devascularization or nerve damage can result. To guarantee that the digit preserves a functional digital artery, just one side of the digit must be operated on at a time.

Devascularization can lengthen healing and recovery durations or, in the worst-case scenario, necessitate amputation. Multiple approaches have been published to address digital nerve injury in the situation of nerve injury, including primary nerve repair, repair using neural conduit, and nerve grafting. Even after treatment, digital nerve damage might result in loss or decreased digital feeling.

Nonoperative therapy may result in decreased dexterity and function in the hands. Nonoperative treatment or monitoring of syndactyly between digits of different lengths may result in greater deformity and development disruption. The shorter digit may exert a tethering effect on the larger digit, causing it to bend in an angular direction toward the shorter digit as well as to flex.

Conclusion 

Syndactyly is a genetic limb deformity characterized by the fusing of certain fingers and/or toes. Syndactyly can be observed on its own or in conjunction with other anomalies. Unreleased syndactyly can affect finger and hand function severely. When the syndactyly is extensive, complicated, or involves the border digits with fingers of irregular lengths, such as the ring and small fingers or the thumb and index finger, the impairment is severe.

If the sole concern is an incongruous look, a slight incomplete syndactyly is not a reason for surgery. However, a syndactyly that restricts full range of motion in the concerned fingers necessitates surgical release to improve finger functioning. The majority of syndactyly patients benefit from surgical release. The date of surgery varies; however, if more fingers are involved and the syndactyly is more complicated, release should occur sooner.