he prevalence of clubfoot approximates 1 in 1000 births, and the male:female ratio is 2:1 (Carey, 2003; Pavone, 2012). Clubfoot is bilateral in approximately 50 percent of afected individuals, and associated anomalies are present in at least 50 percent of all cases (lvfammen, 2004; Sharma, 201i1). Frequently associated anomalies include neuraltube defects, arthrogryposis, and myotonic dystrophy and other genetic syndromes. In cases with associated anomalies, aneuploidy is found in approximately 30 percent. In contrast, the rate is <4 percent when clubfoot appears isolated (Lauson, 2010; Sharma, 2011). hus, a careful search for associated structural abnormalities is warranted, and chromosomal microarray analysis may be considered.
FIGURE 10-47 Foot position. A. Normal fetal lower leg, demonstrating normal position of the foot. B. With talipes equinovarus, the foot "print" is visible in the same plane as the tibia and fibula.
Documentation of the arms and legs is a component of the standard examination. he absence or hypoplasia of all or part of one or more extremities is a limb-reduction dect. he birth prevalence is 4 to 8 in 10,000 (Kucik, 2012; Stoll, 2010; Vasluian, 2013). Approximately half of these are isolated defects, up to on� third occur as part of a recognized syndrome, and individuals in the remaining cases have other coexisting anomalies (Stoll, 2010; Vasluian, 2013). Upper extremities are afected more frequently than lower ones. Of categories, a terminal transverse limb dect lacks part or all of a distal limb to create a stump (Fig. 10-48). his is more common than a longitudinal dect, which is complete or partial absence of the long bone(s) on only one side of a given extremity.
Absence of an entire extremity is termed amelia. Phocomelia, associated with thalidomide exposure, is an absence of one or more long bones with the hands or feet attached to the trunk (Chap. 12, p. 246). Limb-reduction defects are associated with numerous genetic syndromes, such as Roberts syndrome, an autosomal recessive condition characterized by tetraphocomelia. A clubhand dormiy, usually from an absent radius, is associated with trisomy 18 and is also a component of the thrombocytopenia-absent radius syndrome (Fig. 13-5B, p. 258). Limb-reduction defects may occur in the setting of a disruption such as amnionic-band sequence (Chap. 6, p. 116). hey have also been associated with chorionic villus sampling when performed before 10 weeks' gestation (Fig. 14-6, p. 294).
During the past two decades, three-dimensional (3-D) sonography has gone from a novelty to a standard feature of most modern ultrasound equipment (Fig. 10-49). 3-D sonography is not routiney used during a standard examination nor considered a required modality. However, it may be a component of specialized evaluations.
Most 3-D scanning uses a special transducer developed for this purpose. After a region of interest is identiied, a 3-D volume is acquired that can be rendered to display axial, sagittal, coronal, or oblique images. Sequential "slices" may be generated, similar to computed tomographic (CT) or MR images. Unlike two-dimensional (2-D) scanning, which appears to be in "real time," 3-D imaging is static and obtained by processing a volume of stored images. With our-dimensional (4-DJ sonography, also known as real-time 3-D sonography, rapid reconstruction of the rendered images conveys the impression that the scanning is in real time.