Key Wordssyndactyly, webbed digits, syndactyly classification, syndactyly release, complicated syndactyly, Apert hand, Poland syndrome, acrosyndactyly
Syndactyly is the most common congenital hand deformity, presenting with varying levels of severity. Left untreated, syndactyly can result in hand deformity and/or failure of the hand to reach its full functional potential. Surgical treatment typically occurs within the first 2 years of life or earlier (3–6 months) in the setting of border or multiple-digit involvement. Conditions associated with syndactyly, including Apert syndrome or Poland syndrome, are common, especially in more complex cases, and should be worked up and treated appropriately. Reconstruction of syndactyly often requires use of a proximally based dorsal web space flap and interdigitating skin flaps. The use of full-thickness skin grafts permits the surgeon to cover the added circumference after release, allow for a tension-free closure, and preserve digital fat in an effort to match the size of the adjacent, unaffected fingers. Post-operative splinting and care along with long-term follow-up are important for the prevention and management of complications.
Syndactyly of the hand is defined as incomplete separation or fusion of digits. Syndactyly is typically classified based on the length of union from the web space to fingertip and on whether there is bony fusion. Simple syndactyly exists when the digit fusion consists of only a skin and soft tissue bridge. Complex syndactyly encompasses fusion of adjacent phalanges or interposition of accessory bones. Syndactyly is considered to be complete when it involves the full length of the involved digits, and incomplete when only part of the digit is involved. Complete syndactyly can also include a common fingernail, which is termed synonychia . Fusion of multiple digits is often associated with a syndrome.
Syndactyly is the most common congenital hand malformation, classified as a failure of differentiation during embryonic development. It is commonly seen in hand clinics throughout the world, including in low- and middle-income countries. During the fifth week of development, radial condensations of mesoderm within the digital plate form the fingers, which are initially joined by interdigital tissue. This interdigital tissue undergoes a planned apoptosis from distal to proximal, and by the end of the sixth week, the interdigital space is formed. Disruption in protein signaling affecting the apoptotic cascade, and consequently the separation of the digits, represents one potential mechanism in the formation of syndactyly.
The incidence of syndactyly is 3 to 10 in 10,000 births and has been reported to be as high as 10 to 40 in 10,000 births. Although syndactyly may occur sporadically, the majority of cases are inherited as autosomal dominant with variable or reduced penetrance. Other inheritance patterns include autosomal recessive and X-linked recessive, both of which tend to present with more clinically severe forms of syndactyly. Syndactyly tends to be more common in males over females, and unilateral presentation is equally as common as bilateral presentation.
The presence of syndactyly may be associated with syndromes or other conditions. Syndactyly may present with skeletal manifestations including cleft hand, symbrachydactyly, and synpolydactyly. Fourth web space syndactyly is commonly associated with oculodentodigital dysplasia, which consists of optic nerve hypoplasia, small teeth with numerous caries, and a narrow midface. Acrocephalosyndactyly is found in Apert and Pfeiffer syndromes and consists of complex multiple-digit syndactyly, craniosynostosis, and midface hypoplasia. Symbrachydactyly consists of a hypoplastic hand with short fused digits and is commonly associated with absence of the sternal head of the pectoralis major muscle in Poland syndrome. Lastly, as a result of amniotic band sequence, acrosyndactyly can occur, which consists of incomplete digit fusion with proximal sinus tracts. It is critical to identify syndromes pre-operatively to rule out cardiopulmonary or bleeding issues that may lead to significant perioperative complications.
Before operating on a patient with syndactyly, a thorough understanding of web space anatomy is important. A normal web space is U-shaped with a 45-degree slope extending from the metacarpal head dorsally to the mid portion of the proximal phalanx palmarly. Common digital arteries arise from the superficial palmar arch to form proper digital arteries at the web space. The ulnar and radial digital proper arteries of adjacent digits share the same common digital artery. Each web space (except the first web space) also shares a common digital nerve that branches into two proper digital nerves more proximal than arterial bifurcation. A superficial dorsal venous system contributes to a majority of venous outflow, draining into both the cephalic and basilic veins in the arm.
Importantly, the pathological web space anatomy in syndactyly includes a deficiency of skin. The circumference of two joined digits is 22% less than that of the sum total circumference of two separated digits ( Fig. 5.1.1 ). As such, the need for additional skin graft coverage to assist in closure after digit separation almost always exists.
Physical examination is important for determining hand function and allows for appropriate surgical planning. Initially, it should be noted whether the syndactyly is complete or incomplete and simple or complex. Accurate assessment of nail plate involvement should be performed. Any flexion contracture or angular deformity, especially with involvement of border digits, should be documented. The interphalangeal and metacarpophalangeal joints should be measured in both active and passive range of motion. Most importantly, the global functioning of the pre-operative hand should be assessed to determine need for surgery.
In the vast majority of cases, two independently functioning digits will outfunction two fused digits. However, in some complex or complicated cases, connected digits are more stable than when separated. In these cases, function always trumps form, and surgery would not be indicated. Such decisions mandate careful examination. Other contraindications to surgery include release of webs associated with super digits. The two common types are (1) two metacarpals supporting a single oversized digit and (2) a single metacarpal supporting two or more digits. In these cases, separation often fails because one digit becomes stiff, atrophic, and/or cosmetically unacceptable.
In addition to a complete physical examination, plain radiographs of the hand are often helpful in the setting of complex syndactyly to confirm skeletal deformities. This may be particularly helpful in the presence of interposition of accessory bones. For complex cases, such as seen in Apert syndrome or Poland syndrome, pre-operative imaging may also be useful for surgical planning. Plain radiographs are rarely needed before release of simple syndactyly.
The optimal timing of surgery in cases of syndactyly is variable depending on the health of the child and the digits involved. Despite parents’ desire to have the fingers separated as soon as possible, simple syndactyly involving a single web space is often operated on between 12 and 24 months of age. Early surgery may increase the risk of scar contracture, and delayed surgery may result in finger deformity from angulation or flexion contractures. The exception to this is when border digits (index/thumb and ring/small) are involved. In these cases, the length discrepancy can lead to significant rotational deformity and flexion contracture with continued growth of the digits, necessitating release between 3 and 6 months of age.
When multiple digits are involved, such as in the case of Apert syndrome, careful consideration must be given to protecting the blood supply to the digits. Only one side of a digit at any time should be operated on to prevent vascular compromise. Typically, release of border digits can be done first to allow for restoration of tripod pinch. A slightly different approach releases all web spaces in two stages. The first surgery releases the first and third web space, which is followed by a second surgery 4 to 6 months later to release the second and fourth web space.
For routine syndactyly release, no special equipment is required. The ideal surgical setup would include a non-sterile tourniquet, a hand table, a basic hand instrument pan (including a scalpel, fine pickups, double-hook retractors, and a tenotomy scissors), 5-0 vicryl and 5-0 chromic sutures, along with casting/splinting materials. A general anesthetic is required. For non-syndromic cases, there are no specific anesthesia concerns.
The goals of syndactyly treatment are to create a normal web space and improve the function and appearance of each finger. There have been over 46 different techniques described for digital separation. This chapter will detail a common approach to syndactyly release.
Release of simple complete syndactyly:
A proximally based dorsal rectangular flap for web space reconstruction is designed ( Fig. 5.1.4 ).
The metacarpophalangeal joints are flexed to 90 degrees, and the metacarpal heads are marked on the dorsum of each digit to be released.
A point 2/3 the distance of each proximal phalanx from the marked dorsal metacarpal heads is marked. This point should be slightly off midline, cheated toward the web space.
These points are connected to form a proximally based flap with the base at the level of the metacarpal heads.