Congenital Pseudarthrosis of the Clavicle

Idiopathic congenital pseudarthrosis of the clavicle refers to the presence of a fibrous tissue-filled gap within the clavicular shaft in a patient with no evidence of fibrous dysplasia or neurofibromatosis. There are hyaline cartilage caps at the bony margins of the defect, with fibrocartilage occupying the remainder of the defect. Congenital pseudarthrosis of the clavicle almost always occurs on the right or is bilateral (10%). Isolated involvement of the left clavicle is usually accompanied by situs inversus and dextrocardia. Cervical ribs occur with an increased frequency in these patients. Rarely, a familial occurrence is present.^1,2

The pathogenesis of congenital pseudarthrosis of the clavicle may involve bony resorption due to pulsation of a nearby artery in the developing fetus. Other postulated pathophysiologic etiologies include failure of coalescence of the 2 centers of clavicular ossification or a defect in the primary ossification center of the clavicle. The most common clinical presentation is that of a painless lump of the midportion of the clavicle. (Pain is common in patients with nonunion of a clavicle fracture.) Rarely, there are symptoms of thoracic outlet syndrome.³

Congenital pseudarthrosis of the clavicle appears radiographically as a defect in the midportion of the clavicle, typically at the junction of the mid and lateral thirds (Figure 58-1). There is no visible callus formation. The margins of the defect are well corticated and rounded. The ends of the bones often are somewhat enlarged, particularly in older patients. The lateral segment of the clavicle often has a curved appearance, and is sometimes hypoplastic. The medial segment of the clavicle almost always is superior to the lateral segment, and there usually is slight overriding. An ipsilateral cervical rib is present in some patients.⁴

Additional considerations in the differential diagnosis of clavicle defects are cleidocranial dysplasia and posttraumatic pseudarthrosis. The clavicular defects of cleidocranial dysplasia are almost always bilateral. The gaps tend to be wider than in congenital pseudarthrosis. The remaining portions of the clavicles are often somewhat hypoplastic. There are also coexistent deformities elsewhere in the skeleton (see Chapter 57 for additional discussion of cleidocranial dysplasia). With posttraumatic pseudarthrosis, the bone ends are usually bulbous due to exuberant callus formation. These patients typically have pain with palpation or with shoulder motion.

Sprengel Deformity

Sprengel deformity is due to failure of descent of the scapula during fetal development.⁵ Normally, the scapula assumes its position below the T3 level by the third gestational month. Sprengel deformity is usually unilateral. There is a female predilection. Potential associated anomalies include spinal fusion anomalies (20%), scoliosis (30%), spinal dysraphism (5%), and rib anomalies (30%). Between 20% and 40% of patients with Sprengel deformity have Klippel-Feil syndrome (short neck, limited neck mobility, low posterior hairline, cervical spine fusion anomalies). Sprengel deformity can also occur in association with Goldenhar syndrome.⁶

Imaging studies of Sprengel deformity show an elevated position of the involved scapula. The scapula is usually abnormally rotated and medially displaced as well (Figure 58-2). In some patients, an anomalous bone extends between the scapula and the cervical spine; this is the omovertebral bone (see also Figure 22-9). For selected patients, detailed imaging of the pathological anatomy with CT or MR is helpful for surgical planning.⁷

Congenital Dislocation of the Radial Head

Congenital dislocation of the radial head can occur as an isolated anomaly (unilateral or bilateral) or in association with 1 of a variety of syndromes (e.g., osteoonychodysostosis, Nievergelt syndrome). Dislocation can occur anteriorly, posteriorly, or, uncommonly, laterally. Radiographs show the radial head to be dome-shaped and the radial neck to be thin. The humeral capitellum is small and dysplastic. There is often convex anterior bowing of the radial shaft in the presence of a congenital posterior dislocation of the radial head (Figure 58-3).

Radial Synostosis

Congenital fusion anomalies involving the radius most often occur between the proximal aspects of the radius and ulna. Less common are distal radioulnar fusion and radiohumeral fusion. Radioulnar synostosis is bilateral in greater than 50% of cases. There is a male predilection. Radioulnar synostosis occurs in association with fetal alcohol syndrome, various chromosomal abnormalities (XXXXY), Nievergelt syndrome (tibial deformities, tarsal coalition, carpal coalition, radioulnar synostosis), and regional musculoskeletal deformities of the upper extremity (hypoplasia, carpal coalition, symphalangism). An autosomal dominant syndrome has been described in which megakaryocytic thrombocytopenia is associated with radioulnar synostosis.⁸

In the embryo, the radius and ulna form from a single block of mesenchyme. Separation of the cartilaginous rods that constitute the embryonic radius and ulna first occurs distally, whereas proximal connecting mesenchyme persists until the second fetal month. Radioulnar synostosis is apparently due to failure of dissolution of this proximal mesenchyme. The connecting mesenchyme chondrifies, and ossification occurs later in childhood.

The synostosis is cartilaginous in young infants, and therefore is radiolucent. The anomaly is suggested clinically by limitation of supination of the forearm. Radiographs show deformity of the radial head. In older children, radioulnar synostosis is demonstrated as bony fusion between the proximal radius and ulna (Figure 58-4). Occasionally, there is a thin nonossified cartilaginous septum between the 2 bones. Typically, the proximal radius has an abnormal tapered configuration, with lack of development of a normal radial head. The shaft of the radius is usually bowed. With radiohumeral synostosis, the elbow joint is usually fixed in a somewhat flexed position. As with other forms of synostosis, there may be a radiolucent cartilaginous gap at the fusion site, particularly in young children.

Developmental Dysplasia of the Hip

Developmental dysplasia of the hip (DDH; congenital dislocation of the hip) encompasses a spectrum of abnormalities in formation of the acetabulum, femoral head, and articular soft tissues that cause abnormal orientation between the femoral head and acetabulum. The prevalence is approximately 10 per 1000 livebirths. Associated risk factors or predisposing conditions for DDH include a positive family history, female gender, breech intrauterine position, oligohydramnios, a large for gestational age fetus, and congenital musculoskeletal deformity. At least 60% of infants with DDH have no identifiable risk factor. Early detection and prompt initiation of effective therapy are essential for optimal outcomes in patients with DDH. Osteoarthritis is a common long-term consequence of this disorder.^9–11

The mildest form of DDH consists of joint laxity, with otherwise normal cartilaginous and osseous development. Terminology that is utilized to describe the dynamics of hip location includes: (1) subluxation, which refers to increased intraarticular motion of the femoral head in response to stress; (2) dislocation indicates complete displacement of the femoral head outside the confines of the acetabulum; and (3) reducibility indicates the potential for a dislocated hip to return to the acetabulum. Acetabular dysplasia indicates an abnormal shallow configuration of the acetabulum, resulting in subnormal covering of the femoral head. Teratological dislocation refers to dislocations that occur early in utero and are nonreducible; these often occur in association with other anomalies.

The pathogenesis of DDH is multifactorial, and includes both genetic and environmental influences. Development of the femoral head and development of the acetabulum (during both fetal development and childhood) are interdependent. Formation of the normal cup-shaped acetabulum requires the presence of a femoral head. Likewise, normal development of a concentric femoral head requires the influences of a morphologically normal acetabulum. Abnormal laxity of fetal or infantile ligamentous tissue may play a role in many instances of DDH. The combined influences of circulating maternal relaxin and intrinsic estrogen may account for the propensity for involvement of females (M:F = 8:1). Intrauterine mechanical factors are also important. Oligohydramnios impedes motion of the fetal hip. Breech presentation is associated with knee extension and the application of sustained hamstring forces to the hip region. Approximately 20% of infants with DDH have a history of breech presentation. An additional potential mechanical factor is the tendency for the fetal left hip to assume an adducted position against the mother’s lumbosacral spine; this may account for the observed greater frequency of dysplasia in the left hip than the right.

The natural history of DDH varies substantially between patients, and is influenced greatly by therapeutic intervention. Mild neonatal hip joint laxity usually resolves spontaneously during the first several weeks of life. Other untreated patients have progressive acetabular dysplasia and developmental femoral head deformity. With long-standing recurrent dislocation or substantial subluxation, secondary adaptive changes occur in the adjacent soft tissues. These include increased pulvinar fat (deep acetabular fibrofatty tissue), hypertrophy of the ligamentum teres and transverse acetabular ligament, shortening and tightening of the abductor and iliopsoas muscles, interposition of the iliopsoas tendon or joint capsule into the hip, and alterations in the acetabular labrum.

In some young infants with hip dysplasia, the labrum becomes everted and there is interposition of capsular tissue between the labrum and the outer margin of the acetabulum. Lacking appropriate therapy, the labrum may eventually become elongated and inverted; the deformed labrum in this situation can block hip reduction. Abnormal mechanical forces at the superior margin of the acetabulum that occur with long-standing hip subluxation or dislocation may result in the formation of fibrous tissue that is contiguous with the hyaline cartilage along the superior-lateral margin of the acetabulum; this is termed the neolimbus.

The most important clinical indicators of possible DDH are based on the Ortolani and Barlow maneuvers. With the Ortolani maneuver, the flexed hip is slowly abducted while exerting an upward force on the greater trochanter; a clunk suggests reduction of a subluxed or dislocated femoral head. The Barlow maneuver is a counterpart, in which subluxability of the femoral head is assessed by applying a posterior force to the flexed femur while monitoring for a clunk sensation. Less reliable clinical signs of hip dysplasia include inguinal skin fold asymmetry, limited abduction of the hip, and gait disturbance or leg length discrepancy (in an older child).¹²

The major radiographic findings of DDH include abnormal lateral and superior orientation of the femoral head with respect to the acetabulum, a shallow configuration of the acetabulum, and delayed ossification of the capital femoral epiphysis (Figures 58-5 and 58-6). Because the neonatal hip is composed almost entirely of cartilage, the radiographic findings at this age are often subtle; normal radiographs in an infant with suspected DDH do not exclude the diagnosis. The use of various lines and angles is sometimes helpful for the radiographic detection and characterization of hip dysplasia:

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  The acetabular angle is a measure of the slope of the ossified portion of the acetabular roof with respect to a horizontal line drawn through the triradiate cartilages, that is, the Hilgenreiner line. The mean acetabular angle in normal neonates is 27 degrees. Dysplasia is suggested by values greater than 30 degrees or substantial asymmetry relative to the contralateral hip. In normal hips, the acetabular angle diminishes with increasing age.

  
  
• 
  

  Displacement of the femoral head can be assessed with use of the Perkin line, which is a vertical line along the lateral margin of the ossified rim of the acetabular roof. The intersection of the Perkin and Hilgenreiner lines divides the hip joint into quadrants. If the capital femoral ossification center (or the medial margin of the metaphysis prior to femoral head ossification) is located in the lower outer quadrant, subluxation is likely. If it is located in the upper outer quadrant, dislocation is likely. Location within the inner 2 quadrants is the normal situation.

  
  
• 
  

  Shenton line refers to a curved line (arc) drawn along the medial margin of the femoral metaphysis and the superior-medial boundary of the obturator foramen. The use of this line is helpful in infants prior to ossification of the femoral head. In the normal hip, the Shenton line forms a smooth curve. The line is interrupted in the presence of subluxation or dislocation.

Sonography is the mainstay imaging technique for the evaluation of infants with known or suspected DDH. It allows visualization of cartilage and soft tissue structures, and avoids the use of ionizing radiation. Real-time evaluation provides an assessment of the hip alterations in response to various stresses. Because normal neonates usually have mild hip instability due to ligamentous laxity, the sonographic examination of infants with mild clinical findings is optimally delayed until 3 to 4 weeks of age. Early sonography is helpful, however, in newborns who have more marked clinical findings; the examination provides accurate confirmation of the diagnosis and assessment of reducibility.^13–15

The sonographic assessment of hip anatomy includes standardized coronal and transverse images. The cartilaginous femoral head appears as a round, moderately hypoechoic structure. The bony margin of the acetabulum is hyperechoic, whereas the articular cartilage and labrum are hypoechoic. In the transverse plane, the femoral head of a normal infantile hip is located directly lateral to the acetabulum; a line drawn through the center of the femoral head passes through the junction of the ischium and the triradiate cartilage. In the coronal plane, at least half of the femoral head is located within the acetabulum; the labrum is superolateral to the femoral head. A subluxed femoral head moves laterally and superiorly relative to the acetabulum. There is compression of the cartilage at the superior margin of the acetabulum (Figure 58-7). With a completely dislocated hip, the acetabulum and the femoral head cannot be imaged in the same coronal plane.

The most useful sonographic measurement of acetabular maturity is the α angle. This is determined from an appropriately positioned coronal image at the deepest portion of the acetabulum. The transducer is manipulated such that the ilium appears as a straight line that is perpendicular to the femoral head and parallel to the transducer. Three lines are created from this image: (1) the baseline passes along the plane of the ilium; (2) the inclination line passes from the lateral margin of the acetabulum to the labrum, parallel to the cartilaginous acetabular roof; and (3) the roofline passes along the plane of the bony acetabular convexity. The α angle is measured at the intersection between the baseline and the roofline. In young infants, a normal α angle is at least 60 degrees; 50 degrees to 60 degrees is suspicious for disease, and less than 50 degrees is pathognomonic of developmental dysplasia. The β angle has limited clinical utility; this is measured at the junction between the baseline and the inclination line. A normal β angle is less than 55 degrees.

An additional or complementary sonographic technique for assessing the infantile acetabulum is the coverage of the femoral head by the bony component of the acetabulum. This is determined on an appropriately positioned coronal image, as described above for acetabular angle assessment. Two distances are measured from this image: d, the distance between the medial aspect of the femoral head and the baseline; and D, the maximum diameter of the femoral head. The d:D ratio is expressed as a percentage. A normal value is greater than or equal to 58%.¹⁶

A dynamic evaluation during the application of stress maneuvers is an essential component of infantile hip sonography. The Barlow maneuver is applied during real-time observation. Evaluation in the transverse plane is most important. With subluxation, the femoral head displaces posteriorly in response to an adduction stress. The center of the femoral head in this situation is located posterior to the junction of the ischium and triradiate cartilage (Figure 58-8). With a greater degree of subluxation, the femoral head is visualized perched on the acetabular margin. With frank dislocation, the femoral head is displaced posteriorly and overlies the ischium. With coronal imaging, the transducer is rotated such that the posterior margin (posterior lip) of the acetabulum is in the field of view; extension of the femoral head over the margin in response to stress indicates pathological subluxation.^17,18

As described above, mild hip instability should be considered a normal finding in infants during the first few weeks of life. Dynamic sonographic imaging in the transverse plane demonstrates 3 to 4 mm of femoral head motion in most normal neonates; up to 6 mm of motion is generally considered to be within normal limits. This hip laxity likely is related to residual maternal hormonal influences on the ligaments of the hip.

Sonography serves an essential role for the detection of conditions that can mimic the radiographic appearance of developmental hip dysplasia in young infants prior to the femoral head ossification. The femoral head can be substantially displaced laterally in infants with a large hip joint fluid accumulation, such as occurs with pyogenic arthritis. Apparent hip dislocation occurs in infants with epiphyseal separation; the metaphysis is displaced laterally, whereas the unossified femoral head remains within the acetabulum. Epiphyseal separation of the proximal femur in infants can occur in conjunction with child abuse or with lower-force trauma in the presence of infection.

Most infants with DDH are treated with a harness. Intermittent sonography serves to confirm the adequacy of hip location and to monitor improvement in the acetabular morphology. Hip spica casting is the usual treatment for patients initially diagnosed later during infancy (after approximately 6 months of age) and those who fail standard harness therapy. Adequacy of reduction in the presence of a cast is assessed with standard radiographs or (more effectively) with limited CT or MR. Cross-sectional imaging is particularly effective for detecting posterior subluxation. Older children with neglected or recalcitrant hip dysplasia may require operative procedures such as femoral varus derotation osteotomy, capsulorrhaphy, or adductor tenotomy.

CT, MR, and arthrography are sometimes indicated for evaluation of older children with DDH. Arthrography and MR can be utilized to detect impediments to femoral head reduction, such as inversion of the labrum, interposition of the iliopsoas tendon, or thickening of the ligamentum teres. Relatively mild residual lateral subluxation due to prominence of pulvinar fat usually resolves without surgical therapy. Preoperative planning with 3D CT is occasionally useful for patients with advanced deformities. Axial images often demonstrate flattening of the posterior column of the acetabulum (Figure 58-9). MR and bone scintigraphy can be utilized to detect femoral head ischemic necrosis, which is an uncommon complication of hip dysplasia treatment; this presumably is related to compression of the medial circumflex artery against the labrum in patients with forceful prolonged abduction, internal rotation, and flexion.¹⁹

Prenatal Dislocation of the Hip

Intrauterine or prenatal dislocation of the hip is distinct from the much more common postnatal developmental dysplasia of the hip (DDH). When associated with other congenital anomalies (e.g., arthrogryposis, myelomeningocele), prenatal hip dislocation can be termed as a teratological dislocation of the hip. The pathological anatomy of prenatal hip dislocation typically includes articular adhesions and alterations in the ligaments of the hip that prevent reduction. Forced reduction in these infants can lead to ischemic necrosis of the femoral head.

The radiographic features of intrauterine hip dislocation include markedly deficient formation of the acetabulum in conjunction with marked lateral and superior displacement of the femoral head. There is prominent femoral anteversion. Most often, hip involvement is bilateral.

Coxa Valga

Coxa valga refers to lack of the normal varus curve at the junction of the femoral neck and shaft, that is, abnormal straightening of the proximal femur. This deformity is common in nonambulatory patients with chronic neurological or neuromuscular disorders such as cerebral palsy, as weight bearing is necessary for appropriate development of the hip. Spasm of hip flexors and adductors contributes to the deformity. Patients with severe coxa valga often have acetabular dysplasia and chronic hip subluxation (Figure 58-10). As measured on a standard AP radiograph, the mean neck–shaft angle in a newborn is 150 degrees. In older children, the normal neck–shaft angle is 125 degrees to 130 degrees. The mean neck–shaft angle in children with cerebral palsy is 145 degrees to 155 degrees. Rotation and femoral anteversion interfere with accurate measurement of the neck–shaft angle on standard radiographs. CT and MR allow precise measurement when clinically indicated.^20,21

Coxa valga can lead to lateral subluxation or dislocation of the femoral head. Subluxation can cause deformity of the femoral head, often with medial flattening, lateral flattening, or a triangular shape due to medial and lateral flattening. Chronic subluxation can cause acetabular dysplasia and osteoarthritis. Pseudoacetabulum formation can occur with chronic dislocation.

Coxa Vara

Coxa vara is excessive varus angulation of the femoral neck (Figure 58-11). Congenital and developmental forms of coxa vara are idiopathic or, more often, associated with congenital bone pathology. Commonly associated conditions include osteogenesis imperfecta, fibrous dysplasia, and spondyloepiphyseal dysplasia. Acquired coxa vara can occur in children with rickets, trauma, infection, or avascular necrosis. A femoral neck–shaft angle of less than 110 degrees indicates coxa vara. Another method is the Hilgenreiner epiphyseal angle: the angle produced at the intersection of lines drawn through the triradiate cartilages (the Hilgenreiner line) and the proximal femoral physis. The normal value is approximately 25 degrees. The angle is increased in patients with coxa vara.

Developmental Patellar Dislocation

Developmental (congenital) patellar dislocation can occur as an isolated lesion or as part of a generalized dysplasia, such as, arthrogryposis. There is an association of developmental patellar dislocation with Down syndrome. The clinical features of patellar dislocation in infancy range from transient dislocation with knee flexion to a fixed flexion contracture. Most of these patients have genu valgum, flexion contracture, and external rotation of the tibia. Prompt diagnosis and early institution of corrective therapy help prevent long-term sequelae of this anomaly.

Imaging of the knee for suspected patellar dislocation should include flexion and extension views. Dislocation most often occurs laterally. In some patients, dislocation only occurs during flexion. The patella sometimes rotates when dislocated, such that it is opposed to the lateral femoral condyle; a shallow sulcus may develop in the adjacent portion of the condyle. A chronically dislocated patella often is somewhat small and misshapen; visualization of the ossification center may be delayed. Genu valgum is present in nearly all patients with patellar dislocation. The lateral femoral condyle may be flattened and somewhat hypoplastic.

Sonography is sometimes helpful for evaluating infants with suspected developmental patellar dislocation prior to patellar ossification. The cartilaginous patella has a hypoechoic homogeneous character. MR of patients with developmental patellar dislocation defines the associated soft tissue alterations. The quadriceps muscle is usually hypoplastic. The patellar and quadriceps tendons are small. The posterior cruciate ligament may be thinned.²²

Congenital Dislocation of the Knee

Congenital dislocation of the knee is a rare anomaly. This may occur as a sporadic lesion, possibly due to abnormal fetal position, or in association with a dysplasia such as Larsen syndrome, Ehlers-Danlos syndrome, or arthrogryposis. Obvious hyperextension of the knee is present at birth. Radiographs show malalignment at the knee joint, usually with anterior displacement of the tibia with respect to the distal femur. Sonography is an option for dynamic evaluation of joint alignment (Figure 58-12). In older children, potential radiographic findings include hypoplasia of the intercondylar eminence of the tibia, a malformed tibial plateau and femoral condyles, patellar hypoplasia or absence, and genu valgus.

Patellofemoral Instability

Patellofemoral instability refers to a spectrum of conditions in which there is malalignment at the patellofemoral joint. This ranges from mild dynamic malalignment to chronic dislocation. Patellar dislocation and subluxation most often occur along the lateral margin of the femur. In the absence of an acute traumatic event, the pathophysiology of recurrent patellar dislocation and subluxation may be related to ligamentous laxity, vastus medialis insufficiency, a shallow intercondylar notch, genu valgus, patella alta, or external tibial torsion.

The radiographic evaluation of the patient with suspected patellofemoral instability includes standard knee radiographs, as well as a frontal tangential view of the knee in partial flexion (e.g., the merchant, skyline, or Laurin views). A standing radiograph of the lower extremities may also be helpful for the detection of genu valgus. The imaging features of patellofemoral instability include lateral displacement of the patella with respect to the intercondylar notch, as well as tilting of the patella (elevation of the medial margin).

Patellofemoral instability is sometimes associated with patella alta. Patella alta refers to an abnormally superior location of the patella (Figure 58-13). As viewed on a lateral radiograph, the length of the mature patella and the length of the patellar tendon should be approximately equal; patella alta is present if the tendon length (i.e., the distance between the inferior margin of the patella and the superior aspect of the tibial tubercle) is more than 20% greater than that of patella.

Congenital Absence of the Cruciate Ligaments

Congenital absence of the cruciate ligaments can be unilateral or bilateral, and involve the anterior cruciate ligament alone (most common) or both ligaments. Many of these patients have concomitant ipsilateral lower extremity anomalies, such as absent patella, fibular hemimelia, or congenital short femur.²³

Syndactyly

Syndactyly is congenital fusion of adjacent digits. Incomplete syndactyly indicates that the fusion does not extend all the way to the fingertips, as occurs with complete syndactyly. With simple syndactyly, only skin and fibrous tissue or ligaments form the interconnections between the digits. The presence of osseous fusion at any site within the digital interconnection indicates the presence of complex syndactyly (Figure 58-14). Complicated syndactyly refers to disorganized and abnormal neural, muscular, vascular, and bony elements, as occur in some forms of syndromic acrosyndactyly. Acrosyndactyly refers to fusion of the distal portions of the fingers or toes. There are 2 types of acrosyndactyly: (1) amniotic band syndrome, with normal separation of the proximal portions of the digits and fusion of the digits distal to a constricting amniotic band, and (2) a genetic defect in association with other skeletal deformities, the most common of which are Apert syndrome and Carpenter syndrome (Figure 58-15). All patients with Apert syndrome have complex syndactyly of the hands and feet. Metacarpal and tarsal fusions can also occur in these patients (Figure 58-16).^24,25

Polydactyly/Duplication Anomalies of the Digits

Duplication anomalies of the digits range from a rudimentary supernumerary digit to the rare occurrence of 7 or 8 digits. In some instances, there is duplication of only the distal aspect of a digit (Figures 58-17 and 58-14). Polydactyly refers to the presence of extra digits in the hand or foot. Digital duplication anomalies may be due to delayed involution or hyperplasia of the apical ectodermal ridge and failure of programmed death of mesenchymal cells. The apical ectodermal ridge refers to the leading edge of ectodermal cells that cover the mesenchymal cells of the limb bud.²⁶

There are approximately 10,000 new cases of polydactyly annually in the United States. Thumb duplication is more common than that of other fingers. Ulnar polydactyly is much more prevalent in individuals of African descent. Radial (lateral) polydactyly is more common in American Indians and individuals of Asian descent. Ulnar (medial) polydactyly occurs more frequently in males. Central (the second to fourth digits) polydactyly is more common in females. Polydactyly can occur as an isolated deformity or in association with a variety of anomalies and syndromes. Radiographic studies serve to assess the presence or absence of bony fusion and to precisely define the osseous anatomy prior to surgery (Figure 58-18).

Bracket Epiphysis

Bracket epiphysis (longitudinal epiphyseal bracket) is a developmental deformity of a phalanx, metacarpal, or metatarsal that is caused by anomalous extension of the physis along the shaft of the bone. This lesion only occurs in the short tubular bones of the hands and feet that have proximal epiphyseal ossification centers. The thumb is the most common site. Bracket epiphysis can be sporadic or occur in association with fibrodysplasia ossificans progressiva or Rubinstein-Taybi syndrome.^27,28

Radiographs of bracket epiphysis demonstrate an abnormal triangular or trapezoid shape of the involved tubular bone. There is an anomalous arc-like physeal–epiphyseal complex along the bone shaft, most often medially. The bone is foreshortened and asymmetrically widened. MRI is often helpful for depicting the anomalous physeal cartilage (Figure 58-19).²⁹

Split Hand-Foot Malformation

Split hand-foot malformation (ectrodactyly; cleft hand; cleft foot) is a congenital splitting of the hand or foot into 2 halves by a central defect. There is considerable variation in the severity of this condition. Most often, there is a V-shaped defect in the soft tissues that extends at least to the distal aspect of the metacarpal row. The phalanges in the region of the cleft are absent. The central metacarpals/metatarsals are absent or separated (Figure 58-20). Tarsal or carpal deformities (fusions) are common. Syndactyly is also common. The remaining digits often curve toward the cleft.

Split hand-foot malformation can be isolated or occur in association with any of myriad syndromes. There are at least 6 different genetically distinct forms of isolated split hand-foot syndrome. The most common syndromic form is the ectrodactyly-ectodermal dysplasia-cleft lip/palate syndrome, a rare autosomal dominant condition that includes ectrodactyly, ectodermal dysplasia, and facial clefts. Other potential abnormalities are nasolacrimal duct obstruction, decreased pigmentation of hair and skin, vesicoureteral reflux, dental anomalies, conductive hearing loss, and renal anomalies. There is also a rare sporadic form of split hand-foot malformation in which there is a large U-shaped defect of each hand; the feet are usually spared.^30,31

Madelung Deformity

Madelung deformity consists of interrelated abnormalities of the radius, ulna, and carpal bones. The proximal aspect of the radius is foreshortened and bowed (Figure 58-21). There is marked volar and ulnar angulation of the radiocarpal articulation, that is, medial and anterior tilt of the articular surface of the radius. The distal aspect of the ulna is slightly deformed, and is usually dislocated posteriorly. The proximal carpal row may assume a triangular configuration (Figure 58-22). Madelung deformity is thought to be initiated by abnormal diminished growth of the medial aspect of the distal radial physis.

Clinically, patients with Madelung deformity have diminished extension and supination of the wrist. The dislocated distal ulna is palpable dorsally. Clinical presentation does not usually occur until late childhood. The abnormality is much more common in girls than in boys. The deformity is most often bilateral. Most instances of Madelung deformity are idiopathic. Secondary forms can occur due to trauma or bone infection. The abnormality also occurs in association with a variety of syndromes, such as dysostosis multiplex, Turner syndrome, dyschondrosteosis, and enchondromatosis.

Ulnar Variance

Ulnar variance refers to foreshortening (negative ulnar variance) or elongation (positive ulnar variance) of the distal portion of the ulna relative to the distal radius (Figures 58-23 and 58-24). In skeletally mature individuals, the articular surfaces of the distal radius and ulna are approximately even, and the tip of the radial styloid projects 9 to 12 mm beyond the level of the ulnar articular surface. Ulnar variance can be idiopathic or secondary to a variety of conditions that impact ulnar or radial anatomy, such as infection, trauma, osteochondromatosis, and juvenile rheumatoid arthritis. Mild ulnar variance is usually of no clinical significance. Substantial negative ulnar variance is associated with lunate avascular necrosis. Positive ulnar variance can lead to damage of the triangular fibrocartilage.