Disorders of the Pediatric Extremities

Failure of formation

Transverse deficiencies

Intercalary deficiencies

Longitudinal deficiencies

Failure of differentiation

Humeroradial and radioulnar synostosis

Carpal and tarsal coalition

Syndactyly

Symphalangism

Duplication

Dimelia of the long bones

Polydactyly

Brachydactyly

Table 2

Anatomic classification of limb deficiencies (based on Gold NB et al. [3])

Complete absence
Partial absence	Intercalary deficiencies
	Transverse deficiencies	Upper arm	With or without nubbins
		Forearm
		Wrist
		Mid-hand
		MCP joints	Digits 2–5, 1–4 or 1–5
	Longitudinal deficiencies	Preaxial	Radius and digit 1
			Radius and digits 1–2
			Digit 1
			Digits 1–2, or 1–3
		Mesoaxial	Digit 2, or 3, or 4
			Digits 2–3, or 3–4, or 2–4
		Postaxial	Ulna and digit 5
			Digit 5
			Digits 4–5, or 3–5
		Complex	Ulna, radius and digit 1
			Digits 1 and 5
			Digits 2 and 5
			Digit 1 and digits 3–5
			Digits 1–2 and 4–5
			Digits 2–5
			Radius and digit 5
			Radius and digits 1 and 5
			Radius and digits 1–4

Congenital disorders of the extremities usually develop between the third and 8th week of embryogenesis, when outgrowth and spatial patterning of the limbs occur. Many different causes have been identified, including genetic defects (e.g., Fanconi anemia), chromosomal abnormalities (e.g., Trisomy 18), environmental exposures (e.g., Thalidomide), placental pathology (amniotic bands) and prenatal diagnostic procedures. There are more than 120 clinical congenital limb disorders listed in OMIM (Online Mendelian Inheritance in Man; www.ncbi.nlm.nih.gov/omim), but in only 40% of them the molecular basis is known. Moreover, for many of the disorders for which a genetic defect is known, there is evidence for genetic locus heterogeneity, with genes remaining to be discovered.

The diagnostic evaluation of a child with a congenital disorder of the extremities starts with a complete physical examination looking for other congenital malformations [2]. Furthermore, a 3-generation pedigree should be taken and a detailed pregnancy history should be reconstructed including drug use, medications, chorionic villus sampling, diabetes, and illness during the first trimester. In case of a transverse defect radiography of the affected limb is indicated and will help to define the extent of bony deficiency. Placental pathology is helpful to identify the presence of amniotic bands. The longitudinal defects are often part of a syndrome or chromosome abnormality. That is why in these cases usually a skeletal survey is required to detect abnormalities of other parts of the skeleton (pointing to a skeletal dysplasia) instead of imaging restricted to the affected and contralateral limb. Ultrasound (US) and Magnetic Resonance Imaging (MRI) can play a role in selective cases, to detect additional non-ossified (cartilaginous) or ligamentous congenital defects [1, 2, 4, 5]. If the child with a longitudinal limb disorder also presents with neurologic abnormalities, a brain MRI is indicated. Furthermore, the parents should be examined for limb anomalies, as these can be very subtle (e.g., mild thumb hypoplasia). Further chromosome and/or molecular investigations depend on the type of congenital disorder. Table 3 gives an overview of the diagnostic strategy of congenital disorders of the extremities.

Table 3

Diagnostic strategy for congenital disorders of the extremities (based on Wilcox WR et al. [2])

Physical examination for other anomalies, 3-generation pedigree, pregnancy history
Transverse deficiencies	Longitudinal deficiencies
Radiography of affected limb Placental pathology US and/or MRI of affected limbs in selected cases	Radiography of affected and contralateral limb, or Skeletal survey US and/or MRI of affected limbs in selected cases Brain MRI in case of neurological signs Physical examination of parents for limb anomalies Chromosomal testing Blood testing, echocardiography (radial deficiency)
	Molecular testing if indicated
Final diagnosis and genetic counseling

In this chapter the most important congenital disorders of the pediatric extremities will be discussed in more detail with a focus on their principal imaging features and correct terminology.

Failure of Formation (Limb Deficiencies)

Transverse Deficiencies (“Congenital Amputations”) [1, 2]

Transverse deficiency of the limb is usually a sporadic event that is thought to be the result of a vascular disruption during embryogenesis. The whole limb (amelia) or different segments (e.g., forearm, hand, digits) may be absent, depending on the level of ischemia and stage of limb development at time of disruption (Fig. 1). Most transverse deficiencies are unilateral but they can present bilaterally in rare syndromes, and in association with other skeletal abnormalities or nonskeletal abnormalities (e.g., tetra-amelia (absence of all four limbs), Roberts’ syndrome(severe and symmetrical reduction of all four limbs with facial abnormalities) , and toxic embryo fetopathies (thalidomide, valproic acid, hydantoins)). Transverse deficiencies can also be caused by amniotic bands, which are thought to be the consequence of intrauterine rupture of the amnion (amniotic band syndrome). The limbs, digits, or other parts of the fetus become entangled in these fibrous constriction bands resulting in limb or digital amputations, or limb deformities. The risk for amniotic band syndrome is increased after chorionic villus sampling, particularly when performed before 10 weeks of gestation. There is an increased prevalence of club feet, which has been reported as high as 31%. On radiographs, a wide spectrum of asymmetrical abnormalities distal to the level of constriction is seen, including amputation or hypoplasia of the whole or part of the limb or digits, as well as soft tissue thickening (owing to lymphoedema) or thinning. Furthermore, one or several encircling fibrous bands may sometimes be visible on radiographs. Sometimes, MRI might be helpful in identifying non-ossified (cartilaginous) structures and soft tissue anomalies, and to detect the course of relevant neurovascular bundles pre-operatively.

Fig. 1

Amniotic band syndrome of the hand. The digits 2–5 show different levels of amputation, aplasia and deformation of bony structures, as well as constrictions of the skin and soft tissue syndactyly

Longitudinal Deficiencies

Radial Deficiency [1, 2, 6, 7]

This is the most common (preaxial) longitudinal upper limb deficiency and includes all degrees of hypoplasia or aplasia of the radius (Fig. 2). Radial deficiency occurs bilaterally as frequently as unilaterally and is often associated with hypoplasia or aplasia of the thumb, absent scaphoid and trapezium, and bowing of the ulna (also known as radial club hand). Other upper limb anomalies that might be seen in association with radial deficiency include humeral hypoplasia, proximal radioulnar synostosis, congenital radial head dislocation, as well as coalition of the radial carpal bones. It is commonly associated with other anomalies or syndromes and frequently has a known genetic cause. Children with radial deficiencies often present with or develop hematologic abnormalities (e.g., Fanconi anemia, and thrombocytopenia absent radius (TAR)). Other well-known disorders or syndromes with radial deficiencies include trisomy 18, Brachmann-de Lange syndrome, Holt-Oram syndrome, and the VACTERL association. The acronym VACTERL stands for a non-random association of Vertebral anomalies, Anal atresia, Cardiovascular anomalies, Tracheoesophageal fistula, Esophageal atresia, Renal anomalies, and preaxial Limb anomalies.

Fig. 2

Radial club hand. There is an aplasia of the radius and thumb as well as a bowing and hypoplasia of the ulna

Ulnar Deficiency [1, 2, 6, 7]

This longitudinal upper limb deficiency is 3–10 times rarer than the preaxial upper limb deficiencies. Ulnar deficiency is usual unilateral and nonsyndromic. It can be associated with hypoplasia or aplasia of the ulnar carpal bones (triquetrum, pisiform, and hamatum), and/or the fourth and fifth digits. Humeroradial synostosis, congenital radial head dislocation, radial bowing, and coalition of the ulnar carpal or metacarpal bones may also be seen. Ulnar deficiencies have been described in combination with femoral and fibular deficiencies, and craniofacial malformations.

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