Developmental Dysplasia of the Hip

Ligamentous Laxity

Ligamentous laxity is related to DDH in several ways. The condition is associated with the development of DDH when laxity is a familial trait. In fact, the racial incidence of laxity may parallel racial predilections for DDH. The newborn’s response to maternal relaxin hormones may explain the higher incidence of DDH among girls. These hormones, which produce the ligamentous laxity that is necessary for the expansion of the maternal pelvis, cross the placenta and induce laxity in the infant. This effect is much stronger in female than in male children.

In 1970, during an extensive genetic study of DDH, Wynne-Davies proposed that heritable ligamentous laxity was one of two major mechanisms for the inheritance of DDH ( Fig. 13.1 ). She believed that this was an autosomal dominant characteristic with incomplete penetrance. The fact that the risk of DDH is 34% in identical twins (i.e., both twins having DDH) but only 3% in fraternal twins also suggests a genetic influence. In Coleman’s study of Navajo families, hip dysplasia in one family member increased the risk for other family members fivefold. Newborns with DDH have also been found to have a higher ratio of collagen III to collagen I as compared with control subjects, which suggests a connective tissue abnormality in those with DDH. In a study of laxity by distraction of the symphysis pubis, infants with DDH had twice the amount of distraction of the symphysis pubis as compared with control subjects.

Several animal studies are relevant to the issue of laxity of the hip capsule. When the hip capsule and the ligamentum teres were removed from dogs, the animals frequently developed dislocated hips. Dislocation would also result if the capsule was mechanically stretched but not removed. Alternatively, removal of the acetabular roof resulted not in hip dislocation but only in a shallower acetabulum than normal. In a classic study of male and female newborn rabbits, only the female rabbit hips dislocated when the knees were splinted in extension; this observation supports the concept of hormonally induced laxity.

Prenatal Positioning

Prenatal positioning is strongly associated with DDH. Although only 2% to 3% of infants are born in breech presentation, 16% of infants with DDH are born in breech presentation. Neonates who were carried in certain breech positions in utero have a significantly higher risk of DDH ( Fig. 13.2 ). The breech effect is most notable when the knees are extended, with an incidence of 20% seen for a single or frank breech. Alternatively, the footling breech position, in which the hips are flexed, is associated with only a 2% incidence of DDH. Lowry and co-workers have shown a significant reduction in the incidence of DDH when the baby is delivered preterm by cesarean section (3.7%) as compared with those delivered vaginally (8.1%).

Experimental studies in which newborn rabbits’ knees were splinted in extension showed a high incidence of hip dislocation. If, in the same rabbits, the hamstring tendons were transected, the hips did not dislocate; this suggests that the pull of the hamstring across the flexed hip was the dislocating factor. The hip is affected by intrauterine position, and delivery by cesarean section does not alter the likelihood of hip dislocation. The incidence of DDH is also higher among first-born children and in those pregnancies that are complicated by oligohydramnios. ^{, ,} These findings suggest that there is an intrauterine crowding effect on the developing hip. This argument is bolstered by the increased incidence of other postural abnormalities (e.g., torticollis, metatarsus adductus) in children with DDH. In addition, the left hip is more often involved than the right. Because the most common intrauterine position has the left hip adducted against the maternal sacrum, some authors believe that this position places the left hip at greater risk for dislocation as compared with the right hip. ^,

Postnatal Positioning

Postnatal positioning is another factor that is associated with DDH. People who wrap their newborn babies in a hip-extended position (e.g., Native Americans who use cradleboards: Fig. 13.3 ) have a much higher incidence of DDH as compared with other populations. ^{, ,} The mechanism of action is believed to be the placement of the hips in full extension against the normal neonatal hip flexion contracture. An archaeologic study of prehistoric adults found a high incidence of DDH (46/1000) which correlated with head molding from cradleboard immobilization. By contrast, people who usually carry their infants astride the hip or in a wrap that flexes and abducts the hips have a lower incidence of DDH as compared with other groups. A group studied more than 40,000 children in Malawi where a back-carry position similar to the Pavlik position is universally used. Over a 10-year period no cases of DDH were found. Postnatal positioning programs have been considered. In one such approach, new parents were given a set of “abduction pants” and wide diapers; a 65% decrease in the incidence of DDH was noted and attributed to the program.

The primary failure of acetabular development has been proposed as a cause of DDH. Early cadaver studies noted that the acetabulum is shallower at birth than during the earlier fetal period ^{, ,} ; full coverage does not occur until 3 years of age. Beals believes that acetabular dysplasia is inherited and that it may be a precursor of dislocation. After birth, the acetabulum becomes deeper throughout childhood, and it eventually covers the head completely. However, other authors have rejected the primary acetabular dysplasia hypothesis. ^,

Racial Predilection

Racial predilection apparently plays a role; certain ethnic groups seem to be predisposed to DDH, whereas others appear to be somewhat immune. Blacks and Asians have relatively low incidences of DDH (0.1 per 1000 to 5 per 1000), ^, whereas whites and Native Americans have higher incidences (15 per 1000).

Normal Hip Development

The hip joint begins to develop at approximately the seventh week of gestation, when a cleft appears in the mesenchyme of the primitive limb bud ( Fig. 13.6 ). These precartilaginous cells differentiate into a fully formed cartilaginous femoral head and acetabulum by the eleventh week of gestation. ^{, ,} The concave shape of the acetabulum is determined by the structure (femoral head) within the acetabulum. If there is a failure during the normal embryogenesis of the hip, the consequence is a major anomaly (e.g., proximal femoral focal deficiency).

At birth, the neonatal acetabulum is completely composed of cartilage, with a thin rim of fibrocartilage called the labrum ( Fig. 13.7 ). The hyaline cartilage of the acetabulum is continuous with the triradiate cartilages, which divide and interconnect the three osseous components of the pelvis (i.e., the ilium, the ischium, and the pubis). The surface of the acetabular cartilage, which abuts the bone of the pelvis, is made up of epiphyseal cartilage in the shape of a hemisphere; it functions as a major growth plate. The growth of this physis is essential for acetabular development, and any damage to the periacetabular area may induce a growth disturbance. ^{, ,} The labrum also contributes significantly to the development of acetabular depth; thus any excision of the labrum during the treatment of DDH is ill advised. The majority of acetabular shape development is determined by approximately 8 years of age. Late acetabular development during adolescence is enhanced by the growth of the secondary acetabular centers such as the os acetabulum.

The proximal femur has a complex and often misunderstood growth pattern. In the neonate, the entire upper femur is a cartilaginous structure in the shape of a femoral head and the greater and lesser trochanters. The development of the proximal segment of the femur occurs through a combination of appositional growth on the surfaces of the upper femur and epiphyseal growth at the juncture of the cartilaginous upper femur and the femoral shaft. In the normal femur, an ossification center appears in the center of the femoral head between the fourth and seventh months of postnatal life. This center grows until physeal closure during late adolescence; at this time, it has become the adult femoral head, and it is covered with a thin layer of articular cartilage. During the period of growth, the thickness of the cartilage surrounding this bony nucleus gradually decreases, as does the thickness of the acetabular cartilage. The thickness of the cartilage accounts for the widened radiographic appearance of a normal hip in a child.

As the child matures, three acetabular epiphyseal centers develop and are responsible for the final contours of the hip socket ( Fig. 13.8 ). The os acetabulum, which is the largest of the three, appears at approximately 8 years of age and forms along the anterior wall as part of the pubis. The acetabular epiphysis, which also ossifies at approximately 8 years of age, forms along the superior edge of the acetabulum as part of the ilium; it fuses when the child is approximately 18 years old. The third center is a small epiphysis in the posterior or ischial area, which develops when the child is 9 years old and fuses when he or she is 17 years old.

Excessive pressure on the cartilaginous upper femur can cause a loss of vascular perfusion, which results in the necrosis of the chondrocytes. Various portions of the femoral head and growth plate can be injured, with the resulting patterns of deformity corresponding with the areas of injury. The greater trochanteric area is usually unaffected; it will continue to grow normally, gradually becoming more proximal than the femoral head. This “trochanteric overgrowth” is actually normal trochanteric growth in the presence of upper femoral “undergrowth.” ^{, ,}

Muscle imbalance can also significantly affect the growth and morphology of the upper femur. Excessive adductor pull or inadequate abductor muscle function results in a valgus deformity of the upper femur. ^{, ,}

Hip Development With Developmental Dysplasia of the Hip

DDH is a gradually progressive disorder that is associated with distinct anatomic changes, many of which are initially reversible. It is a malformation of anatomic structures that have developed normally during the embryologic period. Relatively gentle forces, persistently applied, are probably the cause of such deformations. At birth, the affected hip will spontaneously slide into and out of the acetabulum. For this to occur, the posterosuperior rim of the acetabulum has to have lost its sharp margin and become flattened and thickened in the area over which the femoral head slides ( Fig. 13.9 ). As the head rides in and out of the socket, a ridge of thickened articular cartilage (called the neolimbus by Ortolani) arises along the posterosuperior acetabular wall ( Fig. 13.10 ). The sliding of the head in and out produces a “clunk.” The neolimbus is the structure that produces this feel as the head slides over it. ^{, , ,}

Some hips that are unstable at birth spontaneously reduce and become normal, with complete resolution of the aforementioned anatomic changes. Other hips eventually remain out of the socket permanently, and many secondary anatomic changes take place gradually. The frequency of spontaneous reduction as compared with progressive dislocation is not known.

In those hips that remain dislocated, secondary barriers to reduction develop. In the depths of the acetabulum, the fatty tissue known as the pulvinar thickens and may impede reduction ( Fig. 13.11 ). The ligamentum teres also elongates and thickens, and it may take up valuable space within the acetabulum. The transverse acetabular ligament is often hypertrophic as well, and it may impede reduction. More important, the inferior capsule of the hip assumes an hourglass shape, eventually presenting an opening that is smaller in diameter than the femoral head. The iliopsoas, which is pulled tight across this isthmus, contributes to this narrowing ( Fig. 13.12 ). The capsule also narrows through a “Chinese finger-trap” mechanism. The femoral changes are minimal and include an increase in anteversion and some flattening of the femoral head as it lies against the ilium.

When an attempt is made to reduce the hip against the narrowed hip capsule, the femoral head abuts the cartilaginous acetabular lip, and it tends to push this rim into the acetabulum. It is extremely important to realize that the acetabular structure is not impeding the femoral head from entering the acetabulum. Rather, the constricted hip capsule is forcing the head against the acetabular rim, and the capsule must be released or stretched to allow the head to move beneath the acetabular rim and enter the acetabulum. Clinicians often use the term labrum for this blocking structure, and sometimes they excise it. However, the actual labrum is a thin fibrocartilaginous rim around the periphery of the acetabular cartilage. The blocking structure encountered in patients with DDH is not only the labrum but also a significant portion of the cartilaginous acetabulum itself. This vital cartilaginous acetabular anlage is essential for the normal growth and development of the acetabulum, and it should not be excised.

After the femoral head has been reduced, the acetabular rim may still impede the deep seating of the femoral head because the rim has become thicker than normal. If the head is maintained within the acetabulum, this thickened cartilage will usually flatten out gradually and allow the head to seat deeply. Known clinically as “docking the head,” this phenomenon was described by Severin in 1941. The femoral head itself is usually deformed into a globular shape as a result of pressure against the lateral portion of the acetabulum, and it may not be congruous with the acetabulum at the time of reduction; however, this anatomic situation also eventually resolves if reduction is maintained.

When a stable reduction is obtained, the acetabulum gradually remodels. This remodeling increases the depth of the acetabulum, and the acetabular angle gradually becomes more horizontal. During the acetabular remodeling period, secondary ossification centers often appear prematurely in the acetabulum.

If the hip remains dislocated, additional changes occur during the growth and development of the acetabulum. The acetabular roof becomes progressively more oblique, the concavity gradually flattens and eventually presents a convex surface, and the medial wall of the acetabulum thickens. The acetabulum has been noted to be excessively anteverted in patients with DDH, thus providing diminished coverage of the femoral head. ^, Medial twisting of the whole wing of the pelvis has been demonstrated by magnetic resonance imaging (MRI) in patients with untreated DDH. Medial wall thickening is seen radiographically as a thickening and alteration of the shape of the teardrop body. Although acetabular anteversion is present in the young hip, retroversion of the acetabulum has been found in adolescents and adults with hip dysplasia.

To a point, these changes are reversible, but the exact upper age at which hip reduction will result in normal acetabular development is uncertain. Harris suggested that a hip reduced by the time a patient was 4 years old could achieve “satisfactory” acetabular development. He found that significant acetabular growth continued through 8 years of age.

In adults, the fully dislocated femoral head may lie well above the acetabular margin in a markedly thickened hip capsule; this is the so-called “high-riding dislocation” ( Fig. 13.13 ). The adult dislocated femoral head is oval and flattened medially. The acetabulum is filled with fibrous tissue, hypertrophied ligamentum teres, and thickened transverse acetabular ligament, and the articular cartilage is either atrophic or absent. The muscles that insert at the proximal femur are foreshortened and more horizontally oriented ( Fig. 13.14 ). Fully dislocated adult hips may remain free from degenerative changes for many years, even for the individual’s lifetime.

In some untreated hips, the femoral head retains some contact with the acetabulum. These subluxated hips have an unstable contact area that allows the head to slide proximally and distally against a widened and oblique acetabular surface. This instability produces degenerative changes that often become apparent during late adolescence and that usually progress rapidly within a few years to severe degeneration. Late radiographic changes include subchondral sclerosis and cyst formation in the acetabulum and the femoral head, osteophyte formation, and the loss of articular cartilage. The reorientation of the acetabulum and the redirection of the forces across the hip can ameliorate degenerative changes if they are performed before severe degeneration occurs.

Neonatal Hip Instability

The fate of the unstable hip remains an enigma. How often an unstable hip spontaneously reduces—or, alternatively, becomes dislocated, subluxated, or dysplastic—remains a subject of controversy. A primary problem is the definition of an unstable hip. Traditionally, instability has been defined by a positive result on the Ortolani or Barlow test. However, the classification has been complicated by the inclusion of hips that are clinically stable but that have abnormal ultrasonographic characteristics. Thus the criteria that an investigator uses to define abnormal hips must be taken into consideration when evaluating any study of hip instability.

Barlow found 1 hip in 60 that he examined to exhibit his instability sign; 60% normalized within 1 week, and 88% were corrected within 2 months without treatment. Coleman’s natural history study in Navajo children found that 5 of 23 Ortolani-positive hips spontaneously corrected, with the remainder being dysplastic, subluxated, or dislocated. Yamamuro followed 52 newborns with untreated instability. Three of 12 Ortolani-positive hips resolved, and 24 of 42 subluxatable hips also resolved.

Dysplasia, Subluxation, and Dislocation After the Neonatal Period

The term dysplasia refers to a radiographic finding of increased obliquity and the loss of the concavity of the acetabulum, with an intact Shenton line ( Fig. 13.15 ). The term subluxation is used when the femoral head is not in full contact with the acetabulum ( Fig. 13.16 ). The radiographic findings of subluxation include a widened teardrop femoral head distance, a reduced center–edge angle, and a break in the Shenton line. The term dislocation specifies that the femoral head is not in contact with the acetabulum. Both subluxated and dislocated hips have dysplastic changes.

Dysplasia is a direct result of abnormal forces across the acetabulum. The lateralization of the femoral head results in increased forces over a smaller unit area with an increase in the sheer vector. Increased sheer vectors affect the physes of the acetabulum. With an acetabular inclination of more than 15 degrees, the sheer and lateralization forces exceed the medialization forces, and progressive subluxation is inevitable. Roof osteophytes will form at synovial attachment sites. These progress, forming a pseudoacetabulum that increases the contact surface area of fibrocartilage at the acetabular margin. Joint contact area determines the cartilage stress. Stress may rise from 20 to 320 kp/cm ² .

An abductor lurch is an effective adaptation in that the abductor forces are reduced to the point that only body weight forces are carried through the hip. When the pelvis drops, however, the head coverage decreases, and this has a negative biomechanical effect.

Dysplastic hips without subluxation usually become painful and develop degenerative changes over time. These hips often become subluxated as the degenerative disease progresses. Cooperman and associates reported that all dysplastic hips without subluxation with a center–edge angle of less than 20 degrees sustained osteoarthritic changes over 22 years of follow-up ; however, no direct correlation of the center–edge angle with the development of arthritis was demonstrated. It has been shown that a hip with an acetabular angle of 35 degrees or more 2 years after reduction has an 80% probability of becoming a Severin class III or IV hip, which will likely require later hip replacement. It is estimated that 20% to 50% of cases of degenerative arthritis of the hip are the result of subluxation or residual acetabular dysplasia. ^d

d References , , , , , , , .

The only guarantee of a lifetime of normal hip function is a completely normal radiographic appearance of the hip.

The subluxated hip always leads to symptomatic degenerative hip disease. ^{, , , ,} The affected individual often presents with gradually increasing pain in one or both hips but no history of hip symptoms or treatment. After the pain begins, it tends to progress rapidly over a period of months. Severe subluxation leads to symptoms during the second decade of life, moderately subluxated hips become painful during the third and fourth decades, and the least severely subluxated hips become symptomatic during the fifth and sixth decades. ^, In one study, the hips with well-developed false acetabula had the highest incidence of pain and disability.

A completely dislocated hip causes symptoms much later than a subluxated hip; in some individuals, these hips never become painful. No strict linear relationship between center–edge angle, acetabular angle, and osteoarthritis has been found. ^, Hip, knee, and back pain have been noted in approximately half of the patients with untreated DDH. Other studies have emphasized cases in which there were no symptoms or few symptoms despite lifelong hip dislocation. ^{, ,}

Other degenerative and functional problems develop in people with untreated dislocated hips. ^{, , , ,} Unilateral dislocations cause limb length inequality, ipsilateral valgus knee deformity, an abnormal gait, decreased agility, and postural scoliosis. Bilateral cases are associated with significant back pain as a result of increased lumbar lordosis.

Neonate

DDH in the neonate is diagnosed by eliciting Ortolani or Barlow sign or from significant changes seen in the sonographic morphology of the hip. The unstable hip may either stabilize spontaneously or become dysplastic or dislocated over a period of several months.

The hip examination ( Box 13.4 ) of the neonate requires an artful approach in which the setting must be controlled and the examiner experienced. The first requisite is a relaxed child. To achieve this, the infant may need a bottle; the examination surface should be warm and comfortable, and the room should be reasonably quiet. A firm examination surface is best, but if the parent’s lap keeps the child more comfortable, it will suffice.

Box 13.4

Physical Examination Findings by Age for Developmental Dysplasia of the Hip

Neonate

• Dislocatable

• Reducible

• Klisic sign

Infant

• Dislocatable (occasionally)

• Reducible (occasionally)

• Klisic sign

• Decreased abduction

• Galeazzi sign

Walking Child

• Remains dislocated

• Klisic sign

• Decreased abduction

• Galeazzi sign

• Limp

• Short leg

• Increased lordosis (bilateral)

The “feel” of this examination is most important, and it is not unlike palpation of the liver. Movement of the hip in and out of the socket is a delicate event that is best appreciated with a very light touch. The examiner holds the child’s knees, one in each hand, and examines one hip at a time.

In the test for Barlow sign, the examiner attempts to slide the femoral head out of the acetabulum ( Fig. 13.17 ). The hip is adducted, and a gentle push is applied to slide the hip posteriorly. The examiner’s fingers are positioned over the greater trochanter, and the trochanter is allowed to move laterally. In a positive test, the hip will be felt to slide out of the acetabulum. As the examiner relaxes the proximal push, the hip can be felt to slip back into the acetabulum.

The Ortolani test is the reverse of the Barlow test: the examiner attempts to reduce a dislocated hip ( Fig. 13.18 ). The examiner grasps the child’s thigh between the thumb and the index finger and, with the fourth and fifth fingers, lifts the greater trochanter while simultaneously abducting the hip. When the test result is positive, the femoral head will slip into the socket with a delicate “clunk” that is palpable but not audible. The examiner should repeat this sequence four or five times to be certain of the findings, alternating the Barlow test and the Ortolani test in a gentle arc of motion. The other hip is then examined in the same manner. During the newborn period, there are usually no other signs of abnormality.

This examination is subject to many factors that can affect its effectiveness and reliability. The hurried examiner usually fails to appreciate the instability. It is possible to examine a hip throughout 15 maneuvers and to feel the instability only the sixteenth time that the hip is moved. The explanation is that this “feel” is quite delicate and requires just the right degree of relaxation on the part of the examiner as well as the infant. Many examiners report a “click”: a high-pitched snap, often felt at the extremes of abduction. This click may originate in the ligamentum teres or occasionally in the fascia lata or psoas tendon, and it usually does not indicate a significant hip abnormality ; however, one study reported a 9.35-fold increase in the incidence of abnormal results on ultrasonography in children with simple clicks, and another found a 1.5% incidence of DDH when a click was the only finding. One study of 256 patients found no abnormalities with this finding.

It is important to plan appropriate follow-up for children after the initial evaluation. Occasionally, patients who had a negative clinical examination during the neonatal period present at an older age with dysplasia ( Fig. 13.19 ). Imaging studies—ultrasonography for the infant and pelvic radiography for the child who is older than 6 months—should be done in children with risk factors that include breech presentation in a girl and positive family history. Whether imaging is necessary for all children who are referred remains unclear.

Infant ( Video 13.1 )

As the child enters the second and third months of life, other signs of DDH appear (see Box 13.4 ). It is important to recall that the progression from instability to dislocation during the newborn period is a gradual process. In some children, an irreducible dislocation develops within a few weeks, whereas in others the hip dislocation remains reducible until they are 5 or 6 months old. When the hip is no longer reducible, specific physical findings appear, including limited abduction, shortening of the thigh, proximal location of the greater trochanter, asymmetry of the thigh folds, and pistoning of the hip.

The limitation of abduction, which is the most reliable sign of a dislocated hip, is best appreciated by abducting both hips simultaneously with the child on a firm surface ( Video 13.2 ). A unilateral dislocation produces a visible reduction in abduction on the affected side as compared with the normal side ( Fig. 13.20 ). Shortening of the thigh (Galeazzi sign) is best appreciated by placing both hips in 90 degrees of flexion and comparing the height of the knees, again looking for asymmetry ( Fig. 13.21 ). Because the thigh is foreshortened, there will be more thigh folds on the affected side than on the normal side ( Fig. 13.22 ). Although this sign is always present with a unilateral dislocation, extra thigh folds are a common normal variant and do not necessarily indicate hip dislocation.

A potentially perilous situation for the unwary examiner is the child with bilateral hip dislocation. This child has no asymmetry of abduction, and the flexed knees are at the same level. Combined abduction is limited, but this is difficult to detect because the limitation is symmetric. One test that can help the examiner to recognize a bilateral dislocation is the Klisic test, in which the examiner places the third finger over the greater trochanter and the index finger on the anterior superior iliac spine. An imaginary line drawn between the fingers should point to the umbilicus. When the hip is dislocated, the more proximal greater trochanter causes the line to point approximately halfway between the umbilicus and the pubis ( Fig. 13.23 ).

These examinations are capricious, and the clinician should use imaging studies to evaluate infants with questionable findings and those with risk factors that are associated with DDH. These risk factors include a family history of DDH, breech position, oligohydramnios, torticollis, and metatarsus adductus. The significantly higher frequency of DDH among girls as compared with boys must also be considered. The reexamination of a child a few months later helps to decrease the possibility of missing a dislocation. It is imperative that experienced orthopaedic practitioners provide education to primary care providers regarding examination for DDH.

Walking Child

The unilateral dislocated hip produces distinct clinical signs in a walking child ( Video 13.3 ; see Box 13.4 ). Although some authors have suggested that children with DDH are late to start walking, more recent studies have shown no significant delay. ^, The affected side appears to be shorter than the normal extremity, and the child toe-walks on the affected side. With each step, the pelvis drops as the dislocated hip adducts, and the child leans over the dislocated hip; this is known as an abductor lurch or Trendelenburg gait ( Fig. 13.24 ). When the child attempts to stand on that foot with the other elevated off of the floor, he or she leans toward the affected side (Trendelenburg sign). As in the younger child, there is limited abduction on the affected side, and the knees are at different levels when the hips are flexed (Galeazzi sign).

In the walking child, bilateral dislocation is more difficult to recognize than unilateral dislocation. There is usually a lurching gait on both sides, but some children mask this rather well, showing only an increase in the dropping of the pelvis during the stance phase. Excessive lordosis is common, and it is often the presenting complaint ( Fig. 13.25 ). The lordosis is the result of hip flexion contracture, which is usually present. The knees are at the same level, and abduction is symmetric but limited. There is usually an excessive internal and external rotation of the dislocated hips.

Ultrasonography

The neonate’s hip is a difficult structure to image with standard radiographic techniques because the hip is composed primarily of cartilage and soft tissue. Ultrasonography is a modality which gives the examiner a detailed view of soft and hard tissues about the hip, both in static and mobile modes. A number of technics are in use and many studies have defined parameters of normal, and indications for treatment.

Graf in 1980 first described his technique using a lateral imaging technique with the transducer placed over the greater trochanter ( Fig 13.26 ). He subsequently developed a classification of abnormalities which is in use today ( Table 13.2 ).

Harcke and Kumar in the 1980s reported dynamic studies in which the hip is moved to reproduce the Barlow and Ortolani maneuvers, and the degree of subluxation is documented with ultrasonography. ^, During the first few days of life, 4 to 6 mm of motion is considered normal, and definite treatment indications developed on the basis of stress views are still evolving. ^,

Tersen in 1989 described an ultrasonic measure of femoral head coverage which has also had wide usage, with a 50% coverage considered to be normal.

A number of recent reviews have compared the several classification systems and their reproducibility. ^,

The Terjesen Method

The main finding of the Terjesen method is the percentage of coverage of the femoral head. The lower normal limit for the coverage value is 50% in infants older than 1 month of age. In addition, the alpha angle of Graf is measured, and the shape of the lateral bony rim is defined as normal, defective, or rounded. The exact percentage of head coverage which requires treatment is as yet not clearly defined ( Figs. 13.27 and 13.28 ).

Radiography

Plain radiography of the pelvis usually demonstrates a frankly dislocated hip in individuals of any age. In newborns with typical DDH, however, the unstable hip may appear radiographically normal. As the child reaches 3 to 6 months of age, the dislocation will be evident radiographically, but the examiner must be familiar with the landmarks of the immature pelvis to recognize the abnormality. In the infant, the upper femur is not ossified, and most of the acetabulum is cartilaginous. The triradiate cartilage lies between the ilium, the ischium, and the pubis.

Several classic lines are helpful when evaluating the immature hip ( Figs. 13.29–13.31 ). The Hilgenreiner line is a line through the triradiate cartilages. The Perkin line, which is drawn at the lateral margin of the acetabulum, is perpendicular to the Hilgenreiner line. The Shenton line is a curved line that begins at the lesser trochanter, goes up the femoral neck, and connects with a line along the inner margin of the pubis. In a normal hip, the medial beak of the femoral metaphysis lies in the lower, inner quadrant produced by the juncture of the Perkin and Hilgenreiner lines. The Shenton line is smooth in the normal hip. In the dislocated hip, the metaphysis lies lateral to the Perkin line; the Shenton line is broken because the femoral neck lies cephalic to the line from the pubis.

Another useful measurement is the acetabular index, which is an angle formed by the juncture of the Hilgenreiner line and a line drawn along the acetabular surface (see Fig. 13.30 ). In normal newborns, the acetabular index averages 27.5 degrees. At 6 months of age, the mean is 23.5 degrees. By 2 years of age, the index usually decreases to 20 degrees. Thirty degrees is considered the upper limit of normal. ^{, ,} The acetabular index of the weight-bearing zone or the sourcil is normally less than 15 degrees. ^,

In the older child, the center–edge angle is a useful measure of hip position (see Fig. 13.31 ). This angle is formed at the juncture of the Perkin line with a line that connects the lateral margin of the acetabulum to the center of the femoral head. In children who are 6 to 13 years old, an angle of more than 19 degrees has been reported as normal; in children who are 14 years old and older, an angle of more than 25 degrees is considered normal.

A helpful radiographic projection is the Von Rosen view, in which both hips are abducted, internally rotated, and extended. In the normal hip, an imaginary line extended up the femoral shaft intersects the acetabulum. When the hip is dislocated, the line crosses above the acetabulum.

The acetabular teardrop figure, as seen on an anteroposterior (AP) radiograph of the pelvis, is formed by several lines. It is derived from the wall of the acetabulum laterally, the wall of the lesser pelvis medially, and a curved line inferiorly, and it is formed by the acetabular notch. The teardrop appears between 6 and 24 months of age in a normal hip and later in a dislocated hip. In a study by Smith and associates, the teardrop did not appear until hips were reduced, but the teardrop was present in dislocated hips by 29 months of age in a study by Albiñana and associates. When the hip is dislocated or subluxated, the acetabular portion of the teardrop loses its convexity, and the teardrop is wider from the superior to the inferior directions. The reduced hip remodels the acetabulum, and the teardrop gradually narrows. Hips in which the teardrop appears within 6 months of reduction have a better outcome than hips in which the teardrop appears later. Four types of teardrop bodies have been noted: open, closed, crossed, and reversed. The teardrops have also been described as U- or V-shaped, with a V-shaped teardrop being associated with a dysplastic hip and a poor outcome ( Fig. 13.32 ).

Another measure of acetabular dysplasia is the acetabular index of depth to width in which the depth of the central portion of the acetabulum is divided by the width of the acetabular opening, with normal being more than 38%. The femoral head extrusion index represents the percentage of the femoral head that lies outside of the acetabulum.

The false-profile radiographic view represents a lateral view of the acetabulum, and it is especially useful for evaluating anterior acetabular dysplasia. ^{, ,} The patient is positioned 65 degrees obliquely to the x-ray beam, with the foot parallel to the cassette. The extent of anterior coverage is represented by a dense line of ossification known as the sourcil, the limit of which is sometimes difficult to define. An acetabular angle can be constructed; the mean value is 32.8 degrees, with a range of 17.7 to 53.6 degrees ( Fig. 13.33 ).

The Severin classification has been used for many years to specify outcome in hips that have been treated for DDH ( Table 13.3 ). However, in 1997, Ward and associates reported poor levels of intraobserver and interobserver reliability when the system was used. The interpretive ambiguities and lack of objective measures emphasize the need for a more reliable scheme.

Although parents may become concerned about radiation exposure during the course of their child’s management, the increase in carcinogenic risks from the cumulative radiographs taken to manage an average DDH case have been estimated to be less than 1%.

Arthrography

The arthrographic anatomy of the hip was well described by Severin in 1941. In the normal hip, the free border of the labrum is easily seen as a sharp “thorn” overlying the femoral head ( Fig. 13.34 ). A recess of joint capsule overlies this thorn. The capsule expands beyond this recess and is then constricted by the ringlike zona orbicularis. In a child with DDH, when the hip is in the dislocated position, the acetabular edge is seen, and the capsule is enlarged as it extends over the femoral head. The capsule is constricted at its middle portion into an hourglass shape by the iliopsoas tendon.

When the hip is placed into a reduced position, it may reduce fully against the acetabular wall, or it may “dock” against the labrum and the capsular constriction of the iliopsoas (see Fig. 13.48B ). When the reduction is deep, the labrum lies flat over the head and has a sharp border. When the head is docked, the labrum is blunted and interposed between the head and the acetabular wall. The ligamentum teres is seen within the joint, and it may be outlined by contrast material. A bulge in the acetabular cartilage beneath the labrum (the neolimbus) may be seen. If the reduction is stable and the hip is immobilized in a safe position, then the femoral head will gradually overcome the capsular tightness. Arthrography repeated 6 weeks later shows the head as being well seated in the acetabulum.

Arthrography should usually be performed with the patient under general anesthesia. We prefer the median, subadductor approach with image intensification ( Fig. 13.35 ). The needle is inserted just beneath the adductor longus, approximately 2 cm distal to its origin. If the starting point is too close to the adductor’s origin, the needle will encounter the inferior portion of the acetabulum rather than the joint itself. The needle is directed medially and aimed toward the contralateral sternoclavicular joint. When resistance is encountered, the position of the needle is noted on the image. The needle should be directed toward the joint space. A small amount of contrast material is injected to be certain that the joint has been entered; the contrast agent should flow freely around the femoral head. Another 1 mL of contrast agent is injected, and the needle is removed. Permanent films should be obtained for each significant position of the hip. It is important to note the positions of maximum stability and instability.

Magnetic Resonance Imaging

MRI affords excellent anatomic visualization of the infant hip, but it is not commonly used because of the expense involved and the need for sedation. Kashiwagi and associates proposed an MRI-based classification of hips with DDH. Group 1 hips had a sharp acetabular rim, and all were reducible with a Pavlik harness. Group 2 hips had a rounded acetabular rim, and almost all could be reduced with a Pavlik harness. Group 3 hips had an inverted acetabular rim, and none was reducible with the harness. MRI findings include the widening of the iliac bone, the lateral drift of the superior and posterior portions of the acetabular floor, the overgrowth of the acetabular cartilage, and the convexity of the posterior portion of the acetabular cartilage. ^,

MRI with gadolinium-contrast arthrography is an important tool for the evaluation of the adolescent patient with hip dysplasia and pain. This technique allows for the evaluation of the condition of the labrum and the articular cartilage of the hip joint. Disruption and tears of the labrum, cartilage delamination, and articular cartilage loss can be identified with this technique. ^,

Treatment of the Neonate