Physicians who specialize in pediatric orthopedics and hand surgery frequently encounter congenital hand abnormalities, despite their relative rarity. The treating physician should be aware of the associated syndromes and malformations that may, in some cases, be fatal if not recognized and treated appropriately. Although these congenital disorders have a wide variability, their treatment principles are similar in that the physician should promote functional use and cosmesis for the hand. This article discusses syndactyly, preaxial polydactyly and post-axial polydactyly, and the hypoplastic thumb.
Key points
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Although congenital hand anomalies are relatively rare, pediatric orthopedic surgeons and hand surgeons will frequently see them during the course of clinical practice.
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The clinician should be aware of the associated malformations and conditions that may, in some cases, be fatal if not recognized and treated appropriately.
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The goals of surgery are to improve hand function and cosmesis while limiting complications that could impair function long term.
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The surgeon must balance functional, cosmetic, and cultural goals and align those goals with the proper surgical techniques in order to maximize patient and parent satisfaction following surgical intervention.
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This article discusses syndactyly, preaxial polydactyly and postaxial polydactyly, and the hypoplastic thumb.
Introduction
Congenital anomalies of the upper extremity, although less common than congenital heart disease, are noted in approximately 2 per 1000 live births. This incidence varies by country due to higher incidence of certain malformations in patients of certain ethnic backgrounds, such as polydactyly in those of African descent or amniotic bands in Japanese. Although many of these malformations lead to minor functional deficits, they can pose a concern for the parents and lead to psychological distress in children. In addition, the 1-year mortality of patients with hand malformations is 14% to 16% due to associated malformations, often involving the heart, kidneys, or tracheoesophageal complex. Boys are affected more commonly than girls by a 3:2 ratio, and mothers older than 40 years of age are twice as likely to have children with congenital hand differences as those only 10 years younger.
Malformations of the hand and forearm were classified by Swanson in 1964 and adopted by the International Federation of Societies for Surgery of the Hand ( Table 1 ). Although this classification has its use, it is generally hard to use in clinical instances, because patients may be classified into several categories at once, and it does not guide treatment or prognosis. Oberg and colleagues proposed a modified classification based on a more recent understanding of the embryology of congenital hand malformations. Using this classification, malformations are divided into malformations, deformations, and dysplasias, and then further subdivided ( Table 2 ).
| Type I |
|
| Type II |
|
| Type III | Duplication (polydactyly, mirror hand) |
| Type IV | Overgrowth (macrodactyly) |
| Type V | Undergrowth (radial hypoplasia, symbrachydactyly, brachydactyly) |
| Type VI | Congenital constriction ring syndrome (amniotic band syndrome) |
| Type VII | Generalized skeletal abnormalities |
| I: Malformations |
|
| II: Deformations | Constriction ring syndromes, trigger digits |
| III: Dysplasia |
|
| IV: Syndromes |
|
Embryology
Fetal limb development is initiated with the appearance of a limb bud, consisting of undifferentiated mesenchyme, at the lateral body wall 26 to 28 days after fertilization. Subsequently, the limb develops rapidly in a proximal-to-distal direction over the next 4 weeks. Complex interactions between signaling centers orchestrate this embryonic differentiation. The first axis to form in the limb bud is the preaxial-postaxial (radial-ulnar) axis, which is defined by the zone of polarization activity. The next axis to form is the dorsal-volar axis defined by the apical ectodermal ridge (AER). Finally, the AER defines the limb proximal-distal axis and controls interdigital cellular apoptosis. Signaling pathways critical to limb formation include sonic hedgehog (Shh), wingless-type, and fibroblast growth factors. Ectopic Shh expression is a known source of polydactyly because of its role in digit number and identity.
Introduction
Congenital anomalies of the upper extremity, although less common than congenital heart disease, are noted in approximately 2 per 1000 live births. This incidence varies by country due to higher incidence of certain malformations in patients of certain ethnic backgrounds, such as polydactyly in those of African descent or amniotic bands in Japanese. Although many of these malformations lead to minor functional deficits, they can pose a concern for the parents and lead to psychological distress in children. In addition, the 1-year mortality of patients with hand malformations is 14% to 16% due to associated malformations, often involving the heart, kidneys, or tracheoesophageal complex. Boys are affected more commonly than girls by a 3:2 ratio, and mothers older than 40 years of age are twice as likely to have children with congenital hand differences as those only 10 years younger.
Malformations of the hand and forearm were classified by Swanson in 1964 and adopted by the International Federation of Societies for Surgery of the Hand ( Table 1 ). Although this classification has its use, it is generally hard to use in clinical instances, because patients may be classified into several categories at once, and it does not guide treatment or prognosis. Oberg and colleagues proposed a modified classification based on a more recent understanding of the embryology of congenital hand malformations. Using this classification, malformations are divided into malformations, deformations, and dysplasias, and then further subdivided ( Table 2 ).
| Type I |
|
| Type II |
|
| Type III | Duplication (polydactyly, mirror hand) |
| Type IV | Overgrowth (macrodactyly) |
| Type V | Undergrowth (radial hypoplasia, symbrachydactyly, brachydactyly) |
| Type VI | Congenital constriction ring syndrome (amniotic band syndrome) |
| Type VII | Generalized skeletal abnormalities |
| I: Malformations |
|
| II: Deformations | Constriction ring syndromes, trigger digits |
| III: Dysplasia |
|
| IV: Syndromes |
|
Embryology
Fetal limb development is initiated with the appearance of a limb bud, consisting of undifferentiated mesenchyme, at the lateral body wall 26 to 28 days after fertilization. Subsequently, the limb develops rapidly in a proximal-to-distal direction over the next 4 weeks. Complex interactions between signaling centers orchestrate this embryonic differentiation. The first axis to form in the limb bud is the preaxial-postaxial (radial-ulnar) axis, which is defined by the zone of polarization activity. The next axis to form is the dorsal-volar axis defined by the apical ectodermal ridge (AER). Finally, the AER defines the limb proximal-distal axis and controls interdigital cellular apoptosis. Signaling pathways critical to limb formation include sonic hedgehog (Shh), wingless-type, and fibroblast growth factors. Ectopic Shh expression is a known source of polydactyly because of its role in digit number and identity.
Indications/contraindications
For all congenital hand malformations, the primary surgical indication is to improve hand function and cosmesis. Contraindications include patients with surgical reconstruction that interferes with function, such as for a centralization procedure in a patient with poor elbow function or with a primary postaxial pinch. Relative contraindications include separating functionless or stiff digits, whereby reconstruction will only improve cosmesis and not alter function, or adult patients who function well with minor cosmetic deformity. In addition, the cultural aspects of congenital hand malformations should be considered before surgery is performed, because a malformation considered intolerable in one culture may be tolerable or even desirable in another.
Syndactyly
Syndactyly is a narrowed or fused web space between adjacent fingers. Syndactyly occurs in approximately 2 to 3 patients per 10,000 live births, affecting male patients more commonly than female patients. Unilateral presentation is equally as common as bilateral presentation. Heritable forms of syndactyly are transmitted in an autosomal-dominant pattern with variable penetrance and are often associated with syndactyly between the second and third toes. Syndactyly is often classified by the length of the web, where complete syndactyly extends to the tips of the fingers; incomplete syndactyly does not include the fingertips. In addition, complex syndactyly describes bony fusions, which are typically identified with a single nail plate (synonychia), while simple syndactyly describes only soft tissue connections. Formal classification of syndactyly was originally proposed by Temtamy and McKusick, breaking it down into 5 distinct subtypes based on phenotype and the underlying genetic abnormalities. This classification has been expanded many times and now includes 9 types and numerous subtypes.
Syndactyly can be associated with other skeletal manifestations, including cleft hand, symbrachydactyly, and synpolydactyly, where extra digits are syndactylized in the central digits. Syndactyly is also associated with other genetic syndromes, including acrocephalosyndactyly (Apert, Pfeiffer, and Crouzon syndrome), characterized by craniosynostosis, midface hypoplasia, and complex syndactyly that can involve all 5 digits, as well as acrocephalopolysyndactyly (Noack and Carpenter syndrome), manifested by craniosynostosis, syndactyly, and preaxial polydactyly. Fourth web space syndactyly, between the ring and small fingers, is commonly associated with oculodentodigital dysplasia, where patients can have optic nerve hypoplasia, small teeth with numerous caries, and a narrow midface. Amniotic band syndrome or amniotic disruption sequence is often associated with multiple constriction bands, digital amputations, and acrosyndactyly, with digital fusion at the fingertips along with a variably patent web space proximally ( Fig. 1 ).
Surgical Procedure
The treatment of syndactyly requires good preoperative planning and a thorough discussion of the risks and benefits with the family. Syndactyly release should be performed at 3 to 6 months of age only in patients with mismatched finger size where growth is leading to deviation of the fingers. Otherwise, it can be delayed until 1 to 2 years of age. Adjacent web spaces should not be released in the same setting to avoid vascular compromise. A simple, longitudinal separation creates significant scar tissue, which can impede growth and create deformity and joint contractures. Thus zigzag flaps have been advocated to break up longitudinal scar lines. The commissure should be created with supple dorsal skin flaps, and grafts should be avoided in this area to limit scarring and web creep. Furthermore, thumb-index syndactyly separation is more complicated than finger syndactyly and should be treated with a 2 or 4 flap z-plasty for mild narrowing, or with a dorsal rotational advancement flap for isolated complete syndactyly ( Fig. 2 ). It is essential to remember that the decision-making process needs to include input from families as well as the health care team (physician, therapist, and so on), and it often can be dominated by the families’ perspective of the condition.
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A nonsterile brachial tourniquet inflated to no more than 100 mm Hg greater than systolic pressure and the use of a hand table and loupe magnification is recommended.
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A dorsal rectangular or hourglass commissure flap is marked out two-thirds of the length of the proximal phalanx, the width equal to the center of each adjacent metacarpophalangeal joint (MCP) joint ( Fig. 3 ).
Fig. 3
Patient with syndactyly showing a standard rectangular dorsal flap.
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Zigzag flaps are marked out between the midsagittal axis of each digit dorsally and volarly such that the apex of each dorsal flap will interdigitate with the axilla of each volar flap and vice versa ( Fig. 4 ).
Fig. 4
Patient with syndactyly demonstrating the ( A ) dorsal and ( B ) volar alternating triangular flaps.
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For complete syndactyly, double opposing fingertip skin flaps are created for the lateral nail folds via the Buck-Gramcko technique ( Fig. 5 ).
Fig. 5
Patient with syndactyly demonstrating the Buck-Gramcko Flaps used to restore the lateral nail folds.
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The distal bone connection is transected, and the neurovascular bundle is dissected proximally to its bifurcation. If a distal bifurcation of the artery is present, place a microvascular clamp on the artery branch to be ligated and deflate the tourniquet to ensure immediate reperfusion to that digit.
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Distal nerve bifurcation can be addressed with intrafascicular dissection of the nerve branches until sufficiently proximal separation is achieved.
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The commissure flap is inset first, using a fast-absorbable 5-0 or 6-0 suture followed by closure of triangular flaps without tension.
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Areas that cannot be closed, typically along the lateral commissure, should be covered by defatted, full-thickness skin graft. The tourniquet should be deflated before placing dressings to ensure quick reperfusion to the digit.
Postoperative Care
Patients are typically discharged the day of surgery and return in 3 weeks for cast and dressing removal. The wounds are inspected for signs of infection, flap necrosis, or excessive scarring. Patients are encouraged to begin active range of motion (ROM) after cast removal and begin scar and web space massage once wounds have healed. The use of a silicone scar pad has been advocated to improve scar suppleness and appearance. Occupational therapy can be used to help with scar appearance, to help with ROM exercises in young patients, and to alleviate minor postoperative scar contracture.
Complications and Management
The most common immediate complication is vascular compromise to one of the digits. The best management is prevention, including avoiding operating on both sides of the digit in the same setting, and careful choice of digital artery ligation for distal bifurcation. In cases of a white finger after skin closure, warm the finger with warm saline gauze and reassess after 5 to 10 minutes. If reperfusion is delayed, inspect the fingers for tight flaps and release tight sutures as needed. It is always better to add skin grafts to an open wound than to have too much tension on a skin flap. Infection can be seen, especially with loss of skin flaps or grafts, and should be treated appropriately with antibiotics and skin grafts should be repeated as needed. The most common late complication is web creep due to scar contracture at the commissure ( Fig. 6 ). Occasionally this necessitates revision surgery. In addition, bony deformity and nail abnormalities are more common following complex syndactyly release and can be treated with digital osteotomy or lateral nail fold reconstruction.
Outcomes
There are more than 40 different descriptions of flaps used to release digital syndactyly, and most have reported good outcomes in the most patients. Barabás and Pickford recently reported on 144 patients with an average of 5 years of follow-up following syndactyly release via a traditional Flatt technique. They reported 7 cases of graft failure and a 4.2% rate of web creep requiring revision surgery, although they noted that most of the cases with graft failure did not result in significant web creep. Vekris and colleagues reported on the follow-up of 131 patients with an average of 11.5 years of follow-up. They noted worse results in complex syndactyly, in adjacent digits of dissimilar length, in cases of delayed presentation, and with the use of dorsal and palmar triangular flaps rather than a large dorsal rectangular flap. In addition, Lumenta and colleagues reported on 26 patients with average 11.5-year follow-up and noted 7.7% web creep with an additional 42% showing signs of web thickening without creep. An additional 7.7% demonstrated loss of the lateral nail fold without nail abnormality, and 70% demonstrated hair growth from the groin full-thickness skin graft. Short-term follow-up studies are available for several graftless syndactyly releases with similar results in terms of web creep and revision surgery, but long-term results greater than 5 years have not yet been published.
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