Pediatric Upper Extremity Disorders
Andrea H.W. Chan, MD, MA, FRCSC
Kevin J. Little, MD, FAAOS, FAOA
Dr. Little or an immediate family member serves as a board member, owner, officer, or committee member of the American Association for Hand Surgery, the American Society for Surgery of the Hand, and the Pediatric Orthopaedic Society of North America. Neither Dr. Chan nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.
ABSTRACT
Congenital malformations of the hand and arm are the second most common congenital disorders behind cardiac malformations. The classification and treatment strategies for these disorders have improved significantly, coupled with an increased focus on patient-reported outcomes to drive patient-centered and family-centered care. A multidisciplinary team approach is helpful to evaluate the risks and benefits of all treatment plans to optimize patient outcomes.
Keywords: congenital hand malformations; hand differences; pediatric acquired hand conditions; pediatric hand
Introduction
Congenital hand malformations will be seen by all practitioners who take care of pediatric patients. Most patients can function well and adapt to their differences, and the role of the pediatric hand specialist is to help guide caregivers and patients toward maximizing function while minimizing interventions that can disrupt their lives. Different malformations or dysplasias can have specific associations that should be assessed.
Embryology of the Upper Extremity
The upper limb structures appear at very precise embryonic stages, and development is patterned along three interrelated spatial axes (proximodistal, anteroposterior, and dorsoventral) (Figure 1). The upper limb bud, an outgrowth of two mesoderm layers (somitic and lateral plate) and overlying ectoderm, appears 26 days after fertilization following notochord expression of sonic hedgehog (SHH). Following this, cartilage precursor cells localize centrally within the bud, whereas other connective tissue precursor cells (tendon and muscles) localize at the bud periphery. Differentiation into bony or cartilaginous components occurs in a proximal to distal direction beginning with the humerus at day 36 and ends with the distal phalanges at day 50 to form the skeletal elements. This process is mediated by the interplay among a number of important transcription factors (eg, Hox, Sox), growth factors (eg, transforming growth factor beta, bone morphogenetic protein, fibroblast growth factor [FGF]), and other proteins (eg, Wnt). The subclavian-axillary-brachial arteries appear at day 33, and nerve trunks enter the arm shortly thereafter at day 36. At day 47, the fingers begin to separate at the hand paddle and complete separation of the fingers occurs by day 54.1,2,3
There are three linked limb axes that are responsible for the outgrowth and patterning of the upper extremity. The apical ectodermal ridge (AER) is the first signaling axis to appear, and it is located on the tip of the limb bud. The AER is responsible for proximodistal patterning and is primarily mediated by the FGF family. Transverse limb deficiencies can occur as a result of FGF signaling disruption. The zone of polarizing activity is a signaling axis located in the posterior (or ulnar) margin of the limb bud mesoderm. The zone of polarizing activity is responsible for anteroposterior (or radioulnar) limb patterning and is mediated by SHH. Disruption in signaling can result in mirror duplication and polydactyly. The dorsoventral axis exists in the non-AER ectoderm of the limb bud. WNT proteins are largely responsible for patterning and outgrowth in this axis, and disruptions can lead to conditions such as nail-patella syndrome.1,2
The current accepted classification system to describe congenital hand differences is the Oberg-Manske-Tonkin classification, which uses understanding of developmental and molecular biology, axis involvement, and genetic etiology to classify congenital hand differences.4
 Figure 1 Illustration of the upper extremity limb bud demonstrating the three spatial axes of development. The apical ectodermal ridge (AER), an epithelial thickening at the distal tip of the limb bud, is responsible for proximodistal growth, which is mediated by the fibroblast growth factor (FGF) family. The zone of polarizing activity (ZPA), located in the posterior (ulnar) aspect of the limb bud, is the signaling center for the anteroposterior axis, which is mediated by the signaling molecule sonic hedgehog (SHH). The dorsoventral axis is mediated by the Wingless/Integrated (WNT) signaling pathway. |
Symbrachydactyly
Symbrachydactyly is a sporadic unilateral hand difference that results in the failure of formation of fingers. The incidence is 0.6 per 10,000 live births and has a male and left-sided preponderance.5 Although the etiology is unknown, subclavian artery insufficiency occurring before 42 days’ gestational age is the leading hypothesis. This vascular insult likely leads to a disruption of the AER and results in an isolated transverse limb bud deficiency.6
Symbrachydactyly is characterized by the presence of nubbins with rudimentary ectodermal tissue (nail plates, bone, and cartilage). In general, there is relative sparing of the border digits with shortened or absent central digits. Its clinical presentation, however, is highly variable regarding the extent of the central digital hypoplasia, and function and size of the border digits and hand. As such, the classification can be challenging and multiple differential diagnoses should be considered including amniotic band syndrome, ulnar longitudinal deficiency, hypodactyly, Apert syndrome, and central deficiency. Furthermore, although symbrachydactyly occurs sporadically, it can also be associated with Poland syndrome (unilateral aplasia or hypoplasia of the chest wall and pectoralis major). Syndactyly can also be associated with symbrachydactyly (Figure 2). The Foucher classification (Table 1) grades symbrachydactyly based on the presence of a thumb and digits and joint stability and helps guide surgical management.
Treatment focuses on maximizing realistic function and cosmesis, but also guiding acceptance and setting appropriate expectations. Nonsurgical management includes occupational therapy to optimize vocational and avocational skill sets, opposition paddles for stable monodactyly to facilitate pinch, and also to identify and aid those who may experience negative psychological effects. Surgical management is patient specific and largely focuses on optimizing pinch, opposition, grasp, and release as well as cosmesis. This includes syndactyly release and first web space deepening to provide length to the thumb. Additionally, brachydactyly can be treated with a nonvascularized free toe phalanx if adequate soft-tissue coverage is available, vascularized free toe-to-hand transfers particularly for Foucher classification IIIA/IIIB, or distraction lengthening.5,7
 Figure 2 Clinical photograph of an 18-month-old patient with symbrachydactyly of the right hand and associated hypoplasia of the pectoralis major muscle. (Courtesy of Kevin J. Little, MD.) |
Table 1 Foucher Classification for Symbrachydactyly | ||||||||||||||||||
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Radial Longitudinal Deficiency
Radial longitudinal deficiency (RLD) is a spectrum of preaxial (radial-sided) hypoplasia of the upper limb and presents with variable involvement of the humerus, radius, carpus, and thumb. This malformation occurs primarily as a result of a disruption of the anteroposterior (radioulnar) axis and occasionally the proximodistal axis as well. RLD is the most common congenital longitudinal deficiency, occurring in between one in 30,000 and one in 100,000 live births.8 Although most cases are the result of sporadic mutations, autosomal dominant and recessive types exist.8 Additionally, 33% to 44% of RLD is associated with other syndromes, such as Holt-Oram, Fanconi anemia, VACTERL (vertebral defects, anal atresia, cardiac defects, tracheoesophageal fistula, renal anomalies, and limb abnormalities) association, and thrombocytopenia-absent radius.9,10 The more severe the presentation, the more likely there is an associated syndrome.9 It is imperative that patients who present with RLD are evaluated with a thorough musculoskeletal and systemic examination, treated for these syndromes, and referred for genetic counseling (Table 2).
Clinical presentation can range from mild hypoplasia of the thumb to a complete absence of the radial-sided structures. Absence of the radial support results in radial wrist deviation and volar carpal subluxation with variable stiffness of the wrist and digits. Muscles arising from the lateral epicondyle are often absent, contributing to poor wrist extension and a flexed wrist posture. In more severe forms, the ulna can also be shortened and curved, leading to a J-shaped forearm. The elbow can become stiff in extension and the severely radially deviated posture of the wrist actually facilitates hand-to-mouth function.11
The most comprehensive classification for RLD is the Bayne and Klug classification12 with the added type N James modification13 for isolated thumb hypoplasia, and Goldfarb modification14 with the addition of type V for associated humeral involvement (Table 3). The most common type of RLD when the radius is affected is type IV at 27%.13 Type 0 and I can be commonly associated with proximal radioulnar synostosis and congenital radial head dislocation.15
Indications for surgical treatment are variable but typically focus on improving both function and cosmesis, including improving wrist and forearm alignment, wrist and thumb stability, and thumb deficiency reconstruction. Pollicization of the index finger is the gold standard for isolated thumb hypoplasia (type N) with either an absent or rudimentary thumb and an unstable carpometacarpal joint (Blauth grade IIIB-V) when ulnar-sided preference for grasp has not developed. For RLD types 0-II, the first line of treatment often entails stretching and serial splinting. Tendon transfers, centralization, and distraction lengthening of the hypoplastic radius are surgical options to correct wrist deviation and radial height.16 As discussed in a 2021 study, for RLD types III and IV, soft-tissue release with a bilobed flap, centralization, and radialization are the most commonly performed procedures, with centralization generally being preceded by radial soft-tissue distraction17 (Figure 3). In general, active motion and strength as opposed to persistent wrist radial angulation are most important for improved long-term outcome.18
Table 2 Syndromes Commonly Associated With Radial Longitudinal Deficiency | ||||||||||||||||||||||||||||
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Table 3 Bayne and Klug Classification for Radial Longitudinal Deficiency With James Modification | ||||||||||||||||||||||||||||||||||||||||||||||||
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Thumb Hypoplasia
Thumb hypoplasia can occur in isolation, or within the spectrum of RLD in which up to 44% of reported cases are syndromic.9,10,19 As such, a systemic evaluation is critical. As per the Oberg-Manske-Tonkin classification, thumb hypoplasia falls under type I malformation along the anteroposterior (radioulnar) axis in either the entire upper limb or hand plate alone. Clinically, the thumb is smaller, the interphalangeal joint can be stiff
because of extrinsic muscle deficiency, the metacarpophalangeal joint is unstable because of ulnar collateral ligament insufficiency, thenar bulk is diminished and thumb opposition is limited because of intrinsic thenar muscular deficiency, and the first web space is narrowed. The Blauth classification for thumb hypoplasia with the Manske modification20 of grade III is outlined in Table 4. The most common type is complete thumb absence (type V). This grading system is based on progressive anatomic deficiencies and guides surgical management. Thumb reconstruction involves an opponensplasty, thumb ulnar collateral ligament reconstruction, and first web space deepening, and is considered for Blauth grades II and IIIA in the setting of thumb carpometacarpal joint stability. Pollicization of the index finger is reserved for Blauth grades IIIB to V, in which there is either a rudimentary thumb that has an unstable carpometacarpal joint or an absent thumb (Figure 4).
because of extrinsic muscle deficiency, the metacarpophalangeal joint is unstable because of ulnar collateral ligament insufficiency, thenar bulk is diminished and thumb opposition is limited because of intrinsic thenar muscular deficiency, and the first web space is narrowed. The Blauth classification for thumb hypoplasia with the Manske modification20 of grade III is outlined in Table 4. The most common type is complete thumb absence (type V). This grading system is based on progressive anatomic deficiencies and guides surgical management. Thumb reconstruction involves an opponensplasty, thumb ulnar collateral ligament reconstruction, and first web space deepening, and is considered for Blauth grades II and IIIA in the setting of thumb carpometacarpal joint stability. Pollicization of the index finger is reserved for Blauth grades IIIB to V, in which there is either a rudimentary thumb that has an unstable carpometacarpal joint or an absent thumb (Figure 4).
 Figure 3 Clinical photographs from a 3-year-old patient with right hand type IV radial longitudinal deficiency and thumb hypoplasia (A), and after centralization with an Evans bilobed flap (B). (Courtesy of Andrea H.W. Chan, MD.) |
Ulnar Longitudinal Deficiency
Ulnar longitudinal deficiency represents a spectrum of postaxial (ulnar-sided) hypoplasia of the upper limb resulting from disruption of the SHH signaling pathway in the zone of polarizing activity.21 However, because a feedback loop exists between SHH and FGF during upper limb development, thumb hypoplasia can also occur in the setting of ulnar longitudinal deficiency.21 Ulnar longitudinal deficiency is 4 to 10 times less common than RLD occurring with a frequency of one to 7.4 per 100,000.15,22 Most cases are sporadic and unlike RLD, organ anomalies are not associated. Congenital hand differences, scoliosis, phocomelia, fibular deficiency, and proximal focal femoral deficiency, however, are highly associated.
Clinical findings are highly variable and can range from hypoplastic to absent ulna, ulnar-sided digits (up to 90%), carpal bones, humerus, or shoulder girdle; presence or absence of thumb abnormalities (up to 70%), carpal coalitions, syndactyly (up to 30%), metacarpal synostoses, congenital radial head dislocation, and radioulnar synostosis.21,23,24 The degree of upper limb shortening, forearm bowing, and wrist ulnar deviation is also variable. The elbow is usually abnormal and can be fused.
The Bayne classification is most commonly used and is based on the progressive degree of ulnar hypoplasia, ranging from type I (short distal ulna), type II (hypoplastic ulna), type III (total absence with straight radius), and type IV (usually complete absence of the ulna with radiohumeral synostosis and a bowed radius). The classification has been modified to include type 0 to describe abnormalities of the hand and wrist in the absence of forearm pathology.24
Surgical management focuses primarily on optimizing hand pinch and grasp function, including first web space deepening, thumb syndactyly release, thumb metacarpal derotation osteotomy, and syndactyly releases of other digits. Indications for more proximal surgical interventions are less clear and include progressive or fixed ulnar wrist deviation for which excision of the ulnar anlage can be performed and extreme shoulder internal rotation for which humeral derotation osteotomy can be performed.
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