Phocomelia refers to a flipper-like (Greek phoke, meaning “seal”) anomaly with a distal part (also often abnormal) attached proximally with what grossly appears to be the absence of an intermediate segment [3] (Fig. 7.7). This denotation may be applied to both the upper and lower extremities. The hand may appear to be attached to the trunk, or there may be variable intervening segments of bone. Formerly considered a transverse intercalary segmental defect, phocomelia has recently been redefined as a subset of longitudinal deficiency [8]. Phocomelia is subdivided into three groups, based on whether there is proximal radial longitudinal dysplasia, proximal ulnar longitudinal dysplasia, or combined dysplasia, with an absent forearm or—occasionally—also an absent arm.

The digits are frequently abnormal or missing, and the joints are unstable owing to musculoligamentous relaxation or deficit. Other skeletal and systemic anomalies are frequently present (e.g., thalidomide embryopathy, thrombocytopenia-absent radius (TAR), Holt-Oram syndrome, and others [7]). Abnormalities of all four limbs (tetra-phocomelia) are associated with facial dysmorphism in Roberts syndrome. Extreme cases of Poland syndrome may manifest phocomelia, further discussed in Chap. 9.

Several synonyms refer to radial longitudinal deficiency, stressing various aspects of the abnormality, such as its clinical appearance (radial clubhand) or the complete (radial aplasia) or partial (radial meromelia) absence of the radius. From a strictly anatomic point of view, this is an intercalary, longitudinal, radial meromelia, but the terms radial dysplasia or radial longitudinal deficiency are more appropriate, encompassing the accompanying abnormal nerves, blood vessels, muscles, and adjacent joint anomalies or fusion as well.

Radial longitudinal deficiency is often associated with other systemic or musculoskeletal abnormalities and is indeed isolated in only 33 % of patients [9]. Syndromes are present in about 33 %, usually thrombocytopenia-absent radius (TAR) syndrome or VACTERL association (vertebral-anal-cardiac-tracheo-esophageal-renal-limb anomalies) [9, 10]. Holt-Oram syndrome occurs in about 13 %. Cardiac lesions are usually ventricular or atrial septal defects, but pulmonary artery atresia and patent ductus arteriosus are also reported.

Two types of hematologic syndromes are associated with radial longitudinal deficiency. Fanconi anemia is an autosomal recessive aplastic anemia that presents between 2 and 15 years of age. It can be fatal if not treated by bone marrow transplantation. For this reason, all children with radial longitudinal deficiency should undergo a chromosomal breakage test, which can test for Fanconi anemia before the development of any symptoms. Second, congenital amegakaryocytic thrombocytopenia has been reported in frequent association with TAR syndrome. The TAR syndrome may also be associated with dysplastic genu varum, hooking of the lateral clavicle, and primary cranial synostosis (Baller-Gerold syndrome). This is probably an autosomal recessive disorder, and it may be diagnosed by fetal ultrasound. Children with TAR syndrome tend to have normal thumbs (Fig. 7.8), whereas the thumbs of most children with an absent radius (in the absence of TAR) are absent or hypoplastic.

Approximately 33 % of patients have nonsyndromic additional osseous abnormalities. Scoliosis is the most commonly associated abnormality; other associated abnormalities include humeral hypoplasia, proximal radioulnar synostosis, congenitally dislocated radial head, and stiff digits. The likelihood of having associated anomalies increases with the severity of radial longitudinal deficiency. If the radius is completely absent, additional anomalies are present in 80 %, whereas if the proximal humerus is also absent, essentially all children have additional anomalies. If only the thumb is hypoplastic, 35 % of children have additional anomalies [9].

Radial dysplasia occurs in 1 in 30,000 live births and is most common in boys. It is more often sporadic than inherited [11]. Up to 50 % are bilateral. When unilateral, the right side is affected twice as frequently as the left [12]. Radial longitudinal deficiency has been classified into six types based on the extent of radial shortening and the extent to which the thumb and carpus are involved [13] (Table 7.3). The radial anomaly takes three forms. Total aplasia is most common, occurring in 60 % (Fig. 7.9). Partial aplasia occurs in about 20 % and is usually characterized by absence of the distal growth plate and epiphysis, with deformity of the proximal portion (occasionally only the proximal radius is absent). Hypoplasia is defined as diminution in size without segmental absence. More mild deficiencies can present as absence or hypoplasia of the radial carpal bones or the thumb.

Stretching and corrective casting soon after birth may prevent further contracture. Centralization, the procedure to position the carpus on the ulna, is controversial, as it often leads to a stiff, albeit straighter, forearm and wrist, with a high likelihood of complications including growth arrest and recurrent contracture. Lengthening of the radius has been proposed but often requires several surgeries with a high risk of complications. Surgical treatment of the thumb deficiency, including tendon transfers and pollicization, is more commonly performed (Figs. 7.10 and 7.11). In pollicization, a digit (usually the second) is transferred to the position of the thumb and also rotated.

At birth, the ulna is short, typically 60 % of normal, and this relative deficiency persists. Ossification of the distal ulnar epiphysis may be delayed, and it may fuse prematurely. The ulna is bowed with convexity posterior and medial. The humeral-ulnar articulation is frequently abnormal, and the humerus may also be shortened. Both increased laxity and contractures occur. Proximal radioulnar synostosis and congenitally dislocated radial head are commonly associated with cases of relatively mild radial longitudinal deficiency [11].

The wrist joint is often replaced by a mass of unorganized fibrous tissue. The navicular is almost always absent, and the trapezium is missing in about two thirds. However, the capitate, hamate, triquetrum, and ulnar four metacarpals and phalanges are almost always normal. The thumb is absent in up to 75 % of patients and hypoplastic in another 20 % (Fig. 7.13). Occasionally there is a fleshy rudimentary appendage.