Congenital Anomalies of the Hand. Amniotic Band Syndrome.

Introduction and Classification

Congenital anomalies of the hand and upper limb encompass a heterogeneous group of disorders that arise from disturbances of embryological limb development between approximately the fourth and eighth weeks of gestation. The conditions range from minor cosmetic anomalies requiring no treatment, through syndromic disorders associated with cardiac, renal, and hematological abnormalities, to severe deficiencies that affect function profoundly. The orthopedic surgeon involved in pediatric hand care must combine an understanding of embryological development, a working knowledge of the classification systems, an ability to recognize syndromic associations, and a thoughtful approach to the timing and selection of reconstructive procedures. The classical Swanson classification of the International Federation of Societies for Surgery of the Hand (IFSSH), now succeeded by the OMT (Oberg-Manske-Tonkin) classification, divides congenital upper-limb anomalies into seven categories: I, failures of formation; II, failures of differentiation; III, duplication; IV, overgrowth; V, undergrowth; VI, constriction band syndrome; and VII, generalized skeletal anomalies. The OMT classification, updated and adopted by the IFSSH in 2010 and refined subsequently, organizes anomalies by developmental axis (proximodistal, anteroposterior, dorsoventral) and by other malformations and dysplasias; it has the advantage of grounding the classification in current developmental biology but has not entirely displaced the Swanson categories in clinical practice. This chapter uses the Swanson framework, supplemented where appropriate by the OMT terminology, and synthesizes content from Tachdjian’s Pediatric Orthopaedics, Apley & Solomon’s, Miller’s Review, and Netter’s Concise Orthopaedic Anatomy.

Embryological Background

Limb development begins at approximately 26 days of gestation with the appearance of the limb bud, a thickening of mesenchyme covered by ectoderm. Three signaling centers control the patterning of the developing limb: the apical ectodermal ridge (AER) controls proximodistal outgrowth through fibroblast growth factor signaling; the zone of polarizing activity (ZPA) controls anteroposterior (radioulnar/preaxial-postaxial) patterning through Sonic hedgehog signaling; and the dorsal ectoderm controls dorsoventral patterning through Wnt7a and Engrailed signaling. Disturbances of these signaling pathways produce the major congenital anomalies in characteristic patterns: AER disturbances produce transverse deficiencies and longitudinal deficiencies; ZPA disturbances produce preaxial (radial) and postaxial (ulnar) deficiencies; dorsoventral disturbances produce nail-palm anomalies. The fingers and toes individualize between weeks 6 and 8 by apoptosis of the interdigital mesenchyme; failure of this apoptosis produces syndactyly.

Failures of Formation (Swanson I)

Failures of formation are characterized by absent or hypoplastic skeletal elements and can be transverse (perpendicular to the long axis of the limb) or longitudinal (along the limb axis). Transverse Deficiency Transverse deficiency is an amputation-like absence of the distal limb. Congenital transverse deficiency is typically unilateral, sporadic, and not associated with other anomalies. The level of the deficiency varies from the upper arm to the digits. The commonest single level is the proximal forearm. Treatment depends on the level: prosthetic fitting is the principal treatment, with the upper-limb prosthesis typically prescribed at age 6 months as the child begins to develop bimanual function. The decision- making is individualized: many children with transverse deficiencies become highly functional without prostheses, particularly those with shorter residual limbs and those with bilateral involvement. Surgical reconstruction is rarely required. Radial Longitudinal Deficiency (Radial Club Hand) Radial longitudinal deficiency, classically called radial club hand, is a longitudinal deficiency of the preaxial (radial) side of the forearm and hand. The condition ranges from mild hypoplasia of the thumb to complete absence of the radius with severe hand deformity. The Bayne and Klug classification recognizes four types: Type I, short radius (mild distal radial deficiency); Type II, hypoplastic radius; Type III, partial absence of the radius; Type IV, complete absence of the radius. Associated thumb hypoplasia is the rule, classified by the Blauth system. Bilateral involvement is common. The clinical importance of recognizing radial longitudinal deficiency lies in its strong association with systemic conditions: VATER/VACTERL syndrome (vertebral, anal, cardiac, tracheoesophageal, renal, limb anomalies); Holt-Oram syndrome (autosomal dominant, with cardiac defects and TBX5 mutation); Fanconi anemia (with progressive bone marrow failure, treated by stem cell transplantation if recognized early); thrombocytopenia-absent radius (TAR) syndrome; and chromosomal anomalies. Every child with radial deficiency must undergo systematic evaluation including cardiac ultrasound, renal ultrasound, complete blood count with attention to platelets and pancytopenia, chromosomal analysis, and Fanconi anemia testing (chromosomal breakage analysis). This is one of the great teaching points of pediatric hand surgery: the orthopedic finding may be the sentinel sign of a systemic disorder that requires urgent diagnosis and treatment. Treatment of the upper-limb deformity in radial longitudinal deficiency begins with passive stretching and splinting of the wrist in the newborn period. Surgical management depends on the type and the function of the hand. Centralization of the wrist on the ulna (the classical procedure) re-aligns the wrist and the hand, but the long-term outcomes have shown recurrence of the radial deviation and concerns about the cost of permanent loss of wrist motion. Radialization (an alternative procedure that shifts the wrist and hand laterally relative to the ulna but without centralization) and the distraction-frame technique have been developed in response. Thumb hypoplasia is addressed by

pollicization (transfer of the index finger to the thumb position) in severe hypoplasia or aplasia, with the index finger reshaped, rotated, and shortened to function as a thumb. Ulnar Longitudinal Deficiency Ulnar longitudinal deficiency is less common than radial deficiency and less often associated with systemic syndromes; the association with cardiac, hematological, and renal anomalies is rare. The deficiency may range from mild ulnar shortening to complete absence of the ulna with severe hand and elbow involvement. The Bayne classification of ulnar deficiency recognizes four types analogous to the radial classification. Associated anomalies include syndactyly of the ulnar digits, hypoplasia or absence of the fourth and fifth digits, and unstable or fused elbow. Treatment is individualized to the specific deformity and may include excision of an unstable fibrocartilaginous ulnar anlage in early infancy (the anlage prevents normal elbow and forearm development), corrective osteotomies of the radius, and reconstruction of the hand deformities. Cleft Hand (Split Hand) and Symbrachydactyly The “cleft hand” describes a hand with a central deficiency of one or more central digits, typically with a V-shaped cleft extending into the palm. The classical typical cleft hand (autosomal dominant, often with foot involvement, with normal but absent central rays) is distinguished from the atypical cleft hand (sporadic, often associated with symbrachydactyly, with hypoplastic remnant digits in the cleft). Treatment of typical cleft hand combines soft-tissue closure of the cleft, correction of any associated thumb-index syndactyly, and pollicization or other thumb reconstruction in severe deficiency. The Snow-Littler procedure is the classical reconstruction. Symbrachydactyly — a poorly formed hand with hypoplastic short digits — is treated by soft-tissue release of any syndactyly, transfer of toe phalanges to the hand for digit reconstruction in severe cases, and prosthetic fitting where indicated. Phocomelia Phocomelia is the rare longitudinal deficiency in which the hand attaches directly to the trunk or to a markedly shortened upper limb. The deficiency was classically associated with thalidomide exposure during pregnancy in the 1960s; modern cases are sporadic and uncommon. Treatment is principally prosthetic.

Failures of Differentiation (Swanson II)

Failures of differentiation are characterized by skeletal elements that have formed but have not separated from each other properly. Syndactyly Syndactyly is the failure of separation of adjacent digits, with an incidence of approximately 1 in 2,000 live births. The condition is classified by the extent of fusion (complete: extending to the fingertips; incomplete: partial fusion not reaching the fingertips) and by the tissue involvement (simple: skin and soft tissue only; complex: with bony fusion).

Syndactyly may be sporadic or familial, and is associated with several syndromes including Apert syndrome (acrocephalosyndactyly with craniosynostosis and complex syndactyly of all four limbs), Poland syndrome (unilateral absence of the pectoralis major with simple syndactyly and brachydactyly), and constriction band syndrome (acrosyndactyly with distal fusion of digits secondary to amniotic banding). The treatment principle for syndactyly is surgical separation, typically performed between 12 and 24 months of age for digital separations and earlier (before 6 months) for border digits with significant length discrepancies (thumb-index, ring-little) that would otherwise produce growth deformity. Surgical technique involves a zigzag incision (W-plasty) to avoid scar contracture, careful separation of the digits with preservation of both neurovascular bundles, reconstruction of the web with a dorsal rotation flap or volar flap, and skin grafting (typically full-thickness skin graft from the groin) to cover the lateral aspects of the separated digits. The principle of operating on only one side of a finger at a time, never simultaneously on both sides of a single digit, is preserved to avoid devascularization and prevents simultaneous operation on multiple webs in the same hand in most cases. Camptodactyly Camptodactyly is a non-traumatic flexion deformity of the proximal interphalangeal joint of a digit, most commonly the fifth finger. The condition is often bilateral and may be familial. Camptodactyly is classified as infantile (presenting in the first year of life, usually bilateral, equal sex distribution) or adolescent (presenting at puberty, typically unilateral, female predominance). The pathology involves a combination of skin, fascial, tendon, and joint contractures. Treatment is initially conservative with stretching and splinting; surgical management is reserved for severe or progressive contracture and involves release of the affected tissues, often with skin grafting and tendon adjustment, with variable success. Clinodactyly Clinodactyly is a coronal-plane angular deformity of a digit, most commonly affecting the fifth finger and most commonly in a radial direction at the distal interphalangeal joint. The condition is associated with a delta-shaped middle phalanx — a wedge-shaped phalanx with an oblique physis that produces angular growth. Mild clinodactyly requires no treatment. Severe clinodactyly may be addressed by excision of the delta-shaped phalanx with bone grafting, by physeal-bar resection, or by closing-wedge or opening-wedge osteotomy.

Radioulnar Synostosis Congenital radioulnar synostosis is a failure of separation of the proximal radius and ulna, producing a fixed pronated forearm with no rotation. The condition is bilateral in approximately 60% of cases. Presentation is in childhood with functional limitation in activities requiring forearm rotation (eating, washing, dressing). Treatment is conservative in mild cases, with attention to compensatory shoulder and trunk motion. Surgical management for severe cases involves derotational osteotomy to position the forearm in a more functional position (typically slight pronation in the dominant arm, slight supination

in the non-dominant arm); attempted release of the synostosis with interposition of fat or muscle has had disappointing long-term results because of frequent recurrence.

Duplication (Swanson III)

Polydactyly Polydactyly is the presence of supernumerary digits, classified as preaxial (thumb side), postaxial (little-finger side), or central (within the body of the hand). Postaxial polydactyly is the most common type globally, with an incidence of approximately 1 in 3,000 in white European-descended populations and substantially higher (1 in 100-300) in African and African-descended populations. Preaxial polydactyly is most common in Asian populations and has the strongest functional consequences. Postaxial polydactyly is divided into Type A (a well-formed extra digit on a stable joint with neurovascular supply) and Type B (a rudimentary digit attached by a narrow soft-tissue pedicle). Type A is treated by formal surgical excision with reconstruction of the supporting structures; Type B is treated by simple ligation in the newborn period (the digit becomes ischemic and falls off over 1-2 weeks) or by formal excision later. Preaxial polydactyly — duplication of the thumb — is classified by the Wassel system into 7 types based on the level of duplication (distal phalanx, proximal phalanx, metacarpal, etc.) and the morphology. Wassel Type IV (duplication at the level of the proximal phalanx, with two distinct phalanges) is the commonest type. Treatment is surgical reconstruction of a functional thumb, typically by ablation of the less-developed thumb with reconstruction of the joint, ligaments, and tendons of the preserved thumb (the Bilhaut- Cloquet procedure combines elements of both thumbs into a single composite thumb, used for symmetric duplications, although the long-term cosmetic and functional results are variable). Pollicization may be used for the case in which neither thumb is reconstructible as a thumb. Central polydactyly (involving the middle three digits) is rare and often associated with syndactyly producing a complex hand deformity that requires individualized surgical management. Mirror Hand and Ulnar Dimelia Mirror hand (ulnar dimelia) is a rare anomaly in which the ulnar side of the forearm and hand is duplicated, with two ulnae and eight to nine fingers in a mirror arrangement, and absence of the thumb and radius. Treatment is individualized to provide a functional hand.

Overgrowth (Swanson IV)

Macrodactyly Macrodactyly is overgrowth of one or more digits, typically affecting the soft tissues and the skeleton. The condition may be isolated or part of a more generalized overgrowth syndrome including neurofibromatosis type 1, lipomatosis, Klippel-Trénaunay syndrome, Proteus syndrome, and the PIK3CA-related overgrowth spectrum. Treatment of

progressive macrodactyly is challenging: epiphysiodesis to limit growth, debulking of soft tissues, ray resection in severe cases, and in extreme cases amputation of the affected digit. The cosmetic and functional outcomes are often suboptimal, and the management requires careful coordination with the family and consideration of the underlying syndromic condition.

Undergrowth (Swanson V)

Thumb Hypoplasia (Hypoplastic Thumb) Thumb hypoplasia is graded by the Blauth classification: Type I (minor generalized hypoplasia with all structures present but small); Type II (absence or hypoplasia of the thenar muscles, narrow web space, ulnar collateral ligament insufficiency); Type IIIA (Type II features plus extrinsic tendon abnormalities, CMC joint stable); Type IIIB (Type II features plus extrinsic tendon abnormalities, CMC joint unstable); Type IV (floating thumb attached by a narrow skin pedicle); Type V (complete absence of the thumb). Treatment is graded to the type. Type I requires no treatment. Type II is treated by opponensplasty (transfer of a tendon to recreate thumb opposition), first web space deepening, and ulnar collateral ligament reconstruction. Type IIIA is treated similarly. Type IIIB and beyond is treated by pollicization of the index finger — a procedure in which the index finger is detached, shortened by removal of the metacarpal, rotated approximately 130°, and reattached at the position of the thumb. The intrinsic muscles of the index are repurposed as thumb muscles. The procedure produces a functional thumb at the cost of the index finger and remains the standard procedure for severe thumb hypoplasia. Toe-to- thumb microvascular transfer is an alternative. Brachydactyly Brachydactyly is shortening of one or more digits, often inherited as an autosomal dominant trait. Several distinct types are recognized by which phalanx or metacarpal is shortened. Treatment is rarely required.

Constriction Band Syndrome (Amniotic Band Syndrome, Streeter Dysplasia)

(Swanson VI) Constriction band syndrome — also termed amniotic band syndrome, Streeter dysplasia, or amniotic disruption complex — is a condition in which strands of amniotic membrane wrap around developing fetal structures and produce a spectrum of deformities including amputations, constriction rings, acrosyndactyly (distal fusion of digits with proximal fenestrations), and limb deformities. The condition is sporadic, not heritable, and not associated with chromosomal or systemic anomalies; the orthopedic surgeon faced with the constriction band syndrome can be reassuring on this point to the family. The pathophysiology is debated. The classical “extrinsic” theory of Torpin (1965) holds that early rupture of the amnion releases strands that entangle developing fetal parts; the alternative “intrinsic” theory of Streeter (1930) holds that the anomalies are produced by primary developmental disturbances and that the bands are secondary phenomena. The

current consensus favors the extrinsic theory for the majority of cases, with the recognition that some cases may have multiple etiologies. The clinical manifestations include: (1) constriction rings, varying from superficial skin grooves to deep grooves through subcutaneous tissue, fascia, and even neurovascular bundles, producing varying degrees of distal swelling, lymphedema, and ischemia; (2) congenital amputations, occurring through the level of the constriction, typically distal but possibly at any level; (3) acrosyndactyly, distal fusion of digits with characteristic proximal sinuses or fenestrations between the bridged digits — distinguishing acrosyndactyly from the usual proximally-fused syndactyly of failures of differentiation; (4) limb-length discrepancy; (5) clubfoot, sometimes associated with constriction bands of the leg; and (6) less commonly, more severe systemic deformities including craniofacial clefts and abdominal wall defects. Treatment is staged according to the severity of the constriction and the urgency of the clinical situation. Severe constriction bands producing vascular or lymphatic compromise require urgent release in the newborn period, with Z-plasty or W-plasty of the skin to prevent linear scar contracture. Less severe bands can be released later, often combined with other reconstructive procedures. Acrosyndactyly is treated by surgical separation of the digits as for typical syndactyly, with attention to the proximal fenestrations. Limb- length discrepancy is managed by epiphysiodesis or other limb-equalization procedures. Congenital amputations are managed by prosthetic fitting and adaptive techniques.

Generalized Skeletal Anomalies (Swanson VII)

The Swanson VII category includes generalized skeletal disorders with hand manifestations, such as the various skeletal dysplasias (achondroplasia, multiple epiphyseal dysplasia, spondyloepiphyseal dysplasia), mucopolysaccharidoses, osteogenesis imperfecta, and many others. The orthopedic management of the hand in these conditions is typically secondary to the management of the underlying systemic disorder.

Trigger Thumb of Childhood

Although not a primary congenital anomaly in the strict embryological sense, the pediatric trigger thumb deserves mention here because of its frequent presentation in the first year of life. The condition involves a stenotic A1 pulley with a thickened nodule of the flexor pollicis longus tendon (the Notta nodule), producing inability to extend the interphalangeal joint. The condition is usually unilateral but bilateral cases occur. The natural history of true congenital trigger thumb (presenting at birth) is uncertain; classical teaching held that spontaneous resolution was rare and that surgical release should be performed by age 1-2 years, but more recent studies have shown spontaneous resolution rates of 30-60% with observation. Modern practice typically involves observation for the first 1-2 years, with surgical release (open transection of the A1 pulley) for cases that do not resolve.

Diagnostic and Management Principles

Initial Evaluation Every child with a congenital hand anomaly requires a systematic evaluation: detailed family history including consanguinity; pregnancy history including teratogen exposure (alcohol, medications, drugs of abuse); careful physical examination of the affected limb, the contralateral limb, all other limbs, the head and face, the trunk, and the back; cardiovascular auscultation; abdominal examination; and consideration of additional investigations based on findings. Systemic syndromes — VACTERL, Holt-Oram, Fanconi anemia, TAR, Apert, Poland — are too consequential to miss, and any child with a major upper-limb anomaly should have at minimum a cardiac evaluation and a complete blood count, with additional investigations dictated by the clinical findings.

Timing of Surgery The timing of reconstructive surgery for congenital hand anomalies is dictated by several considerations: the maturity of the affected structures, the developmental window for hand function (with bimanual function emerging in the second year and fine motor skills in the third and fourth years), the risk of growth-related deformity if the anomaly is not corrected (border digits with significant length discrepancy should be separated early), and family considerations. As a general rule, simple separations of border digits are performed by 6- 12 months, central digital separations by 12-24 months, polydactyly excisions by 12-24 months, thumb pollicization by 12-18 months, and complex reconstructions by 2-3 years. Multidisciplinary Care The care of the child with a major congenital hand anomaly is best provided in a multidisciplinary clinic with pediatric hand surgery, occupational therapy, prosthetics, psychology, and where appropriate genetics, cardiology, and hematology. The family requires ongoing support and education, and the child’s transition through development requires repeated reassessment of function and adjustment of the management plan.

Summary and Take-Home Points

The congenital anomalies of the hand encompass a heterogeneous group of disorders classified by the Swanson system into failures of formation, failures of differentiation, duplications, overgrowth, undergrowth, constriction band syndrome, and generalized skeletal anomalies. The clinical recognition of the principal anomalies — radial and ulnar longitudinal deficiency with their syndromic associations (particularly VACTERL, Holt- Oram, Fanconi anemia, TAR), syndactyly with its association with Apert and Poland syndromes, polydactyly with the Wassel classification of the duplicated thumb, hypoplastic thumb with the Blauth classification, and the amniotic band syndrome — is the basis of pediatric hand practice. Treatment is highly individualized and combines surgical reconstruction (separation, excision, pollicization, opponensplasty) with prosthetic fitting and occupational therapy. The recognition of associated systemic anomalies — cardiac, renal, hematological — and the prompt diagnosis of conditions such as Fanconi anemia is one of the most important contributions of the orthopedic surgeon to the care of the child

with a congenital hand anomaly. The amniotic band syndrome, while devastating in its severe presentations, is sporadic and not associated with chromosomal or hereditary disease, a fact that allows reassurance of the family and focus on the specific reconstructive needs of the affected limb.