Syndactyly Clinical Presentation

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.