The acetabular cartilage complex (Fig. 23-2) is a three-dimensional structure that is triradiate medially and cup-shaped laterally. The acetabular cartilage complex is interposed between the ilium above, the ischium below, and the pubis anteriorly. Acetabular cartilage forms the outer two-thirds of the acetabular cavity, and the nonarticular medial wall of the acetabulum is formed by a portion of the ilium above, the ischium below, and portions of the triradiate cartilage.

Thick cartilage, from which a secondary ossification center, the os acetabulum (discussed later in this chapter), develops in early adolescence, separates the acetabular cavity from the pubic bone (11). The fibrocartilaginous labrum is at the margin of the acetabular cartilage, and the joint capsule inserts just above its rim (14) (Fig. 23-3).

The triradiate cartilage is a triphalangic structure. Each phalangis is composed of very cellular hyaline cartilage. This cartilage contains many canals. Each side of each limb of the triradiate cartilage has a growth plate. One phalangis is oriented horizontally between the ilium and the ischium. One phalangis is oriented vertically and interposed between the pubis and the ischium. The third phalangis is located anteriorly and slanted superiorly between the ilium and the pubis (Fig. 23-4). The triradiate cartilage is the common
physis of these three pelvic bones. Interstitial growth within the triradiate cartilage causes the hip joint to expand in diameter during growth (15).

The entire acetabular cartilage complex is composed of very cellular hyaline cartilage (Fig. 23-3). The lateral portion of the acetabular cartilage is homologous with other epiphyseal cartilages of the skeleton (16). This is important in understanding the normal growth and development and the shape of the acetabulum in skeletal dysplasias and injury. The labrum, or fibrocartilaginous edge of the acetabulum, is at the margin of the acetabular cartilage. The hip joint capsule inserts just above the labrum. The capsule insertion is continuous with the labrum below and with the periosteum of the pelvic bones above.

Articular cartilage covers the acetabular cartilage on the side that articulates with the femoral head. On the opposite side is a growth plate, with its degenerating cells facing toward the pelvic bone that it opposes. New bone formation occurs in the metaphysis adjacent to the degenerating cartilage cells. Growth of the acetabular cartilage occurs by means of interstitial growth within the cartilage and appositional growth under the perichondrium. This fact is most important when considering various innominate bone osteotomies, because surgical injury (by aggressive periosteal stripping or osteotome placement) to this important area may jeopardize further acetabular growth.

In the infant, the entire proximal end of the femur, including the greater trochanter, the intertrochanteric zone, and the proximal femur, is composed of cartilage. Between the fourth and seventh months of life, the proximal femoral ossification center appears. This bony centrum and its cartilaginous anlage continue to enlarge (although at a slowly decreasing rate) until adult life, at which stage only a thin layer of articular cartilage remains over it. The proximal femur and the trochanter enlarge by appositional cartilage cell proliferation (17).

The three main growth areas in the proximal femur are the physeal plate, the growth plate of the greater trochanter, and the femoral neck isthmus (17) (Fig. 23-5). A balance among the growth rates of these centers accounts for the normal configuration of the proximal femur, the relation between the proximal femur and the greater trochanter, and the overall width of the femoral neck. The growth of the proximal femur is affected by muscle pull, the forces transmitted across the hip joint by weight bearing, normal joint nutrition, circulation, and muscle tone (17, 18 and 19). Any alterations in these factors may cause profound changes in the development of the proximal femur (20, 21).

During infancy, a small cartilaginous isthmus connects the trochanteric and femoral growth plates along the lateral
border of the femoral neck and is a reflection of their previous common origin. This growth cartilage contributes to the lateral width of the femoral neck and remains active until maturity.

It is the normal growth of these three physes that determines the femoral neck configuration in the adult. Disturbances in growth in any of these three growth plates, by whatever mechanism, alter the shape of the proximal femur. Hyperemia secondary to surgery or inflammatory conditions may stimulate growth in any or all of these growth plates (17).

The proximal femoral physeal plate contributes approximately 30% to the overall growth in length of the femur and 13% to the growth of the limb. Any damage to or disruption of the blood supply to this plate disrupts the growth at this plate and results in a varus deformity because the trochanter and the growth plate along the femoral neck continue to grow (17, 22). Partial physeal arrest patterns may be caused by damage to the portions of the proximal femoral physeal plate. The relation between the growth of the trochanter and the physis of the proximal femur should remain constant; it is measured by the articular trochanteric distance, which is the distance between the tip of the greater trochanter and the superior articular surface of the femoral head. The greater trochanter is usually classified as a traction epiphysis, depending on the normal abductor pull for growth stimulation. The trochanter, like the proximal femur, grows appositionally.

Experimental studies and clinical findings in humans with unreduced dislocations suggest that the main stimulus for the concave shape of the acetabulum is the presence of a spherical femoral head (10, 16, 23, 24 and 25). Harrison determined that the acetabulum failed to develop in area and depth after femoral head excision in rats (16). He also demonstrated atrophy and degeneration of the acetabular cartilage, although the growth plates of the triradiate cartilage remained histologically normal, as did the length of the innominate bones. These experimental findings are characteristic of humans who have had untreated hip dislocations (Fig. 23-6).

For the normal depth of the acetabulum to increase during development, several factors must act in concert. There must be a reduced spherical femoral head. There must also be normal interstitial and appositional growth within the acetabular cartilage, and periosteal new bone formation must occur in the adjacent pelvic bones (10, 11). The depth of the acetabulum is further enhanced at puberty by the development of three secondary centers of ossification (Fig. 23-7). These three centers are homologous with other epiphyses in the skeleton (11, 16). The os acetabulum develops in the thick cartilage that separates the acetabular cavity from the pubis. The os acetabulum is the epiphysis of the pubis and forms the anterior wall of the acetabulum. The epiphysis of the ilium, the acetabular epiphysis, forms a major portion of the superior edge of the acetabulum. A third, small epiphysis also forms in the ischial region and contributes to its normal growth (11, 16, 26).

Normal acetabular growth and development occur through balanced growth of the proximal femur, the acetabular
and triradiate cartilages, and the adjacent bones. This balance, which is probably genetically determined, may be faulty in DDH. There is ample evidence to suggest that an adverse intrauterine environment also plays an important role in the pathogenesis of hip dysplasia (11, 27, 28, 29, 30 and 31).

In the newborn with DDH, the tight fit between the femoral head and the acetabulum is lost. The femoral head can be made to glide in and out of the acetabulum, with a palpable sensation known clinically as the Ortolani sign (11, 19, 32, 33). DDH in the newborn refers to a spectrum of anatomic abnormalities, from mild dysplastic changes to the severe pathoanatomic changes, that are found in the rare idiopathic teratologic dislocation and more commonly in teratologic dislocations associated with conditions such as myelomeningocele and arthrogryposis.

The most common pathologic change in the newborn with DDH is a hypertrophied ridge of acetabular cartilage in the superior, posterior, and inferior aspects of the acetabulum. This ridge was referred to by Ortolani as the neolimbus (19, 33). The neolimbus is composed of hypertrophied acetabular cartilage (9, 32) (Fig. 23-8). There often is a trough or groove in the acetabular cartilage caused by secondary pressure of the femoral head or neck. It is over this ridge of acetabular cartilage that the femoral head glides in and out of the acetabulum, with the palpable sensation referred to as the Ortolani sign (9, 19, 33).

There is empiric evidence that the pathologic changes are reversible in the typical newborn with DDH, because there is a 95% success rate of treatment using simple devices such as the Pavlik harness and the von Rosen splint (34). These pathologic changes are typical of 98% of DDH cases that occur at or around birth. However, approximately 2% of newborns have teratologic (antenatal) dislocations not associated with a syndrome or neuromuscular condition (26, 29). In these rare cases, the pathologic and clinical findings are similar to those seen in late-diagnosed DDH, which is described later in this chapter.

Acetabular development in treated DDH cases may be different from that described for the normal hip. This is particularly true for late-diagnosed cases. The primary stimulus for normal growth and development comes from the femoral head within the acetabulum (10, 24, 25). When there is a delay in diagnosis and treatment, some aspects of normal growth and development are lost. The femoral head must be reduced as soon as possible, and the reduction must be maintained to provide the stimulus for acetabular development. If concentric reduction is maintained, the acetabulum has the potential for recovery and resumption of normal growth and development for many years (35, 36 and 37).

The age at which a dysplastic hip can still return to “normal” after reduction remains controversial (34, 36, 37, 38, 39, 40, 41, 42, 43 and 44).
The resumption and adequacy of acetabular development is a multifactorial problem that depends on the age at which the reduction is obtained and on whether the growth potential of the acetabular cartilage and the proximal femur is normal. The capacity of the acetabular cartilage to resume normal growth depends on its intrinsic growth potential and whether it has been damaged by the subluxated or dislocated femoral head or by various attempts at reduction. In the patient with DDH who has been treated, especially in late-diagnosed cases, accessory centers of ossification contribute to acetabular development (Fig. 23-9). Accessory centers of ossification in the acetabulum are seen in only 2% to 3% of normal hips, and they rarely appear before 11 years of age. However, among patients treated for DDH, the centers may be present in as many as 60% of hips, usually appearing 6 months to 10 years after reduction (35, 36, 37 and 38, 45) (Fig. 23-9). These accessory centers form in the peripheral acetabular cartilage and may be a primary abnormality of dysplasia or, more likely, they are a secondary abnormality caused by pressure damage from the femoral head and/or neck in the subluxated or dislocated position or by damage secondary to closed or open treatment (see later discussion on obstacles to reduction). In treated DDH cases, these accessory centers of ossification should be sought on every sequential radiograph so as to determine whether acetabular development is progressing, as they may coalesce to form a normal acetabulum (Fig. 23-9). This is an important factor to consider when deciding if surgical intervention is necessary to correct residual acetabular dysplasia. Although the presence of these centers indicates continued growth in the acetabular cartilage, they may be indicative of injury to the cartilage in this area. Their presence does not assure normal acetabular development.

Many factors contribute to DDH. Genetic and ethnic factors play a key role, with the incidence of DDH as high as 25 to 50 in 1,000 live births among Lapps and Native Americans and a very low rate among the southern Chinese population and persons of African descent (30, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59 and 60).

A positive family history for DDH may be found in 12% to 33% of patients who have DDH (31, 46, 60). One study reported a tenfold increase in the incidence of DDH among the parents of index patients and a sevenfold increase among siblings compared with the incidence among the general population (46). There is some suggestion that anteversion of the femoral neck or acetabulum may be an etiologic factor (30, 32, 38, 61, 62 and 63).

The genetic effects on the hip joint in patients with DDH are revealed as primary acetabular dysplasia, various degrees of joint laxity, or a combination of both. Intrauterine mechanical factors, such as breech position or oligohydramnios, and neuromuscular mechanisms, such as myelomeningocele, can profoundly influence genetically determined intrauterine growth (5, 6, 64, 65). The first-born child is more likely to be affected than subsequent children. Any of the factors contributing to an “adverse” intrauterine environment may influence the development of the hip joint, and postnatal influences may also contribute to the development of DDH (5, 31, 66, 67, 68 and 69).

Whites show an increased incidence of DDH among first-born children (8, 27, 28, 70, 71, 72 and 73). The unstretched abdominal muscles and the primigravida uterus may subject the fetus to prolonged periods of abnormal positioning, forcing the fetus against the mother’s spine. This restraint limits fetal mobility, especially hip abduction. The high rate of association of DDH with other intrauterine molding abnormalities, such as torticollis and metatarsus adductus, lends some support to the theory that the “crowding phenomenon” plays a role in the pathogenesis (8, 73, 74 and 75). Oligohydramnios, which is associated with limited fetal mobility, also is associated with DDH (8, 73). The left hip is the most commonly affected hip; in the most common fetal position, this is the hip that is usually forced into adduction against the mother’s sacrum (8, 48, 73).

DDH is more common among girls (80% of cases) and among children delivered in the breech presentation. In the general population, breech presentations occur in approximately 2% to 4% of vaginal deliveries. Carter and Wilkinson (27, 28) reported that 17% of children with DDH had a breech presentation; Salter reported the incidence as 23% (76). Twice as many girls as boys are born breech (77). Fiftynine percent of breech presentations are first-born children (27, 28, 77). Ramsey and MacEwen demonstrated that 1 of 15 girls born breech has evidence of hip instability. In animal studies, the prolonged maintenance of an abnormal position, such as the breech position, is associated with the production of DDH (24, 25).

The postnatal environment may significantly influence the development of DDH. In societies that use swaddling (i.e., hips forced into adduction and extension) in the immediate postnatal period, the incidence of DDH is high, possibly as a result of the forceful positioning of the legs in extension and adduction, counter to normal newborn hip flexion and hamstring contractures (31, 48, 58, 63, 68, 78, 79, 80 and 81).

The influence of hip capsular laxity on the development of DDH has been addressed by many investigators. Newborns with DDH may have capsular laxity. Hip capsular laxity has been implicated in the pathogenesis of DDH, because the diagnostic test for DDH, the Ortolani sign, depends on the head gliding in and out of the dysplastic acetabulum over a ridge of abnormal acetabular cartilage. Proponents argue that because reversible dysplasia can be produced in animals by producing ligamentous laxity, the acetabular dysplasia seen in DDH is a secondary phenomenon (24, 25, 31, 32, 76, 82). LeDamany demonstrated that the acetabulum is shallowest at birth (62).
Ralis and McKibbin confirmed LeDamany’s anatomic work in a small number of patients (82). They too demonstrated that the acetabulum was shallowest at birth and that this, combined with the normal laxity in the joint of the infant, makes the time around delivery a high-risk period for dislocation (82, 83). These anatomic experiments were repeated by Skirving and Scadden in African neonates (30); in the African neonate, the acetabulum was deeper more frequently and in a narrower range, possibly explaining why DDH is almost nonexistent among persons of African descent. This finding also provides indirect evidence that acetabular dysplasia is a primary cause of DDH.

Laxity of the hip joint capsule is often seen in newborn infants and has been documented by ultrasonography (84). The laxity may allow some instability without a positive Ortolani sign. In postmortem examination of seven stillborn infants, the hips demonstrated instability with a negative Ortolani sign; arthrograms demonstrated slight pooling of the contrast media medially. On gross examination, the hip capsules were stretched, and the femoral heads could be pulled slightly away from the acetabula. However, the hips were anatomically and histologically normal, unlike the postmortem findings reported for all infants with positive Ortolani signs (9, 11, 33, 56, 85, 86). In addition to the normal physiologic capsular laxity expected in the newborn, DDH is not a feature of conditions characterized by hyperlaxity, such as Down, Ehlers-Danlos, and Marfan syndromes (33).

Taking into account the epidemiologic and etiologic factors, a high-risk group of patients can be identified. This group includes any patient who has more than one of the factors listed in Table 23-1. If an infant manifests any combination of these factors, the physician should be alert to the possibility of DDH.

The incidence of DDH is influenced by geographic and ethnic factors and by the diagnostic criteria used by the examining physician. Another important factor is the diagnostic acumen of the examiner. The age of the patient at the time of diagnosis must be taken into account, because the physical findings and manifestations of the condition change with increasing delay in diagnosis (8, 9, 11, 31, 33, 56, 73, 84, 85, 86, 87, 88, 89 and 90).

Most patients with DDH are detectable at birth (91, 92). Despite screening programs for newborns, some cases are not detected, and some evidence suggests that a few cases may arise after birth (30, 87, 92, 93, 94, 95, 96, 97, 98, 99, 100 and 101). Moreover, whether acetabular dysplasia is primary or secondary to an unrecognized dislocation or subluxation that has reduced spontaneously remains uncertain.

If the diagnosis of DDH is not made early, preferably in the newborn nursery, secondary adaptive changes develop (47). The most reliable physical finding in late-diagnosed DDH is limitation of abduction (Fig. 23-10). Limited abduction is a clinical manifestation of the various degrees of shortening of the adductor longus that are associated with hip subluxation or dislocation (49). Other manifestations of late-diagnosed DDH may include apparent femoral shortening, also called the Galeazzi sign (Fig. 23-11); asymmetry of the gluteal (115), thigh, or labial folds (116); and limb-length inequality (Fig. 23-12). In patients with bilateral dislocations, clinical findings include a waddling gait and hyperlordosis of the lumbar spine (Fig. 23-13A).

If DDH goes undetected, normal hip joint growth and development are impaired. With increasing age at detection and reduction, and particularly in children older than 6 months, the obstacles (intraarticular and extraarticular) to concentric reduction become increasingly difficult to overcome by simple treatment methods such as use of the Pavlik harness, and closed or open reduction usually must be performed under general anesthesia. Restoration of normal acetabular development is less likely as age at detection increases (26, 32, 44, 111, 115, 116, 117, 118 and 119).

In the late-diagnosed case, the extraarticular obstacles to reduction include the contracted adductor longus and the iliopsoas. These muscles are shortened because of the hip being in the subluxated or dislocated position, allowing secondary muscle shortening.

The intraarticular obstacles to reduction in late-diagnosed DDH include the ligamentum teres, the transverse acetabular ligament, the constricted anteromedial joint capsule, and, rarely, an inverted and hypertrophied labrum (32, 120). The most significant intraarticular obstacle to reduction, however,
is some degree of anteromedial hip capsular constriction (32, 121, 122, 123, 124 and 125). The ligamentum teres may be thickened, and it may become the primary obstacle to reduction in some cases. In children of walking or crawling age, the ligamentum teres may be significantly elongated and enlarged. Its sheer bulk precludes concentric reduction without excision of the ligament. The transverse acetabular ligamentum may hypertrophy secondary to the constant pull of the ligamentum teres on its attachment at the base of the acetabulum (32, 125). This effect decreases the diameter of the acetabulum.

A rare finding, other than in teratologic dislocations, is a true inverted labrum or limbus (i.e., hypertrophied labrum) (122) (Fig. 23-14). The acetabular labrum may be iatrogenically inverted and may be an obstacle to reduction in patients previously treated with unsuccessful closed reductions. Arthrograms are often misinterpreted as showing an inverted labrum (126); the shadow thought to be the inverted labrum or limbus is instead the neolimbus (originally described by Ortolani) (9, 32, 127, 128) (Fig. 23-15). This neolimbus is epiphyseal cartilage and is almost never an obstacle to reduction. It must not be removed, because removal impairs acetabular development (9, 129). If the surgeon feels that this tissue is somehow impairing reduction, it should be radially incised but never excised. The cartilage of the neolimbus may be primarily abnormal or may be damaged by a traumatic open or closed reduction. A response to this damage may be responsible for the appearance of the previously discussed accessory centers of ossification seen in treated cases of DDH (9) (Fig. 23-9).

Although the clinical examination remains the gold standard (130), ultrasonography has gained popularity worldwide as a screening tool. Its cost-effectiveness has yet to be documented for screening for DDH on a wide scale.

The use of ultrasonography in the diagnosis and management of children with DDH remains controversial (131, 132, 133, 134, 135, 136, 137, 138, 139, 140 and 141).
Many proponents strongly recommend that ultrasonography be used as a routine screening tool in the newborn nursery and that it be used extensively in the management of all DDH problems (142, 143 and 144). The use of ultrasonography in orthopaedic practice was pioneered by Graf in Austria in the 1970s (145, 146). Harcke et al. in the United States (147, 148, 149 and 150), Terjesen et al. in Norway (151, 152, 153 and 154), and Clarke in Great Britain (155, 156 and 157) have been the prime evaluators of this tool for the diagnosis of DDH and other hip disorders.

Ultrasonography can be used in two basic ways to evaluate the child with DDH: morphologic assessment and dynamic assessment (158, 159, 160, 161, 162 and 163). The morphologic assessment, as pioneered by Graf, focuses primarily on critical evaluation of the anatomic characteristics of the hip joint (Fig. 23-16). This is accomplished by measuring two angles on the ultrasound image: the α angle, which is a measurement of the slope of the superior aspect of the bony acetabulum, and the β angle, which evaluates the cartilaginous component of the acetabulum. The hip is classified into four types and several subtypes according to various factors (145, 146) (Fig. 23-17). In the evaluation of Terjesen et al., the percentage of acetabular coverage of the femoral head (i.e., percent coverage) is a key measurement (151, 152, 153 and 154).

The morphologic approach to ultrasonography is widely practiced in Europe, but it has been criticized because of substantial interobserver and intraobserver variations in the measurement of angles, particularly the β angle (148).

The availability of equipment with which motion can be observed in real time and in multiple planes provides a means of seeing what occurs during the Ortolani or Barlow maneuver. The use of dynamic ultrasonography, as popularized by Harcke et al. (147, 148 and 149), has been criticized for being excessively operator dependent and requiring a subjective assessment of the findings.

The indications for ultrasonography in the diagnosis and treatment of DDH are not universally established. Because there are many controversies yet to be resolved, ultrasonography cannot be advocated as a routine screening tool, even though (148) it is used as such in Europe and in many centers around the world. Prospective longitudinal studies documenting the outcomes of minor anatomic abnormalities found in ultrasonographic examinations need to be completed (164, 165). Its routine use in newborn nurseries has resulted in overdiagnosis (above the expected incidence) of DDH and cannot be considered cost-effective (166, 167, 168 and 169). Its use in only high-risk infants may eventually prove cost-effective (169, 170 and 171). However, Clarke et al. showed that screening all high-risk infants and all infants who had any abnormality on physical examination did not reduce the prevalence of latediagnosed cases (156, 157, 172).

Some centers advocate the use of ultrasonography in all Ortolani-positive infants to assess stability at the completion of treatment (148). An ideal use for ultrasonography is for “guided reduction” of a dislocated hip in an infant (173), in other words, for monitoring the progress of reduction of a subluxated or dislocated hip being treated in a Pavlik harness. Ultrasonography is used at 7- to 10-day intervals to check the progress of reduction of the hip and its stability during Pavlik harness treatment. This may temporarily obviate the need for radiographic evaluation. Other uses for ultrasonography in the treatment of DDH include monitoring of the hip position while the patient is in traction before attempting reduction and evaluating closed reductions in the operating room. The distinct advantage of ultrasonography is that it provides some anatomic evaluation of the hip joint without exposing the infant to radiation.

Debate continues regarding the appropriate planes for evaluation and whether an orthopaedic surgeon, the treating physician, or a radiologist with expertise in ultrasonography
should perform the evaluation. In the newborn, DDH is not a radiographic diagnosis; the diagnosis should be made by clinical evaluation, which may be enhanced by ultrasonography if the examination results are questionable. Some investigators have used vibration arthrometry (174, 175 and 176).

After the newborn period (4 to 6 weeks of age), the diagnosis of DDH should be confirmed by radiography. Many radiographic measurements can be made, but there are wide interobserver and intraobserver variations in these measurements (177, 178). Because it is difficult to standardize the radiographic positioning of infants, many centers use positioning frames (179).

When monitoring the treatment of children with DDH, it is essential to notice changes in the radiographic measurements over time and not to make significant decisions based on a single radiograph. The classic radiographic features of late-diagnosed DDH include an increased acetabular index (29, 180, 181, 182, 183, 184 and 185), disruption of the Shenton line, a widened pelvic floor (186, 187), an absent teardrop figure (188, 189, 190, 191, 192, 193 and 194), delayed appearance of the femoral ossific nucleus on the involved side or dissimilar sizes of the ossific nuclei, abnormality in Smith centering ratios (24, 25, 37), decreased femoral head coverage, and failure of the medial metaphyseal beak of the proximal femur, and, subsequently, the secondary ossification center, to be located in the lower inner quadrant defined by the Hilgenreiner and Perkins lines (89, 195, 196) (Fig. 23-18A). When the triradiate cartilage is closed, the acetabular angle of Sharp (i.e., from the inferior edge of the teardrop figure to the edge of the acetabulum) is a useful measurement of acetabular dysplasia (197).

In children younger than 8 years, the acetabular index is a reasonable measure of acetabular development (177). Measurement of the center-edge (CE) angle becomes useful only in the patient who is more than 5 years of age and is most useful in the adult patient (45) (Fig. 23-18B). Radiographs show only the ossified portion of the pelvic bones and the proximal femur. Excellent acetabular coverage of the femoral head may be found, albeit by unossified cartilage (Fig. 23-19). If this cartilage does not ossify, the residual dysplasia may eventually lead to subluxation and degenerative joint disease.

The Shenton line provides only a qualitative estimate of dysplasia during the first few years of life. After 3 or
4 years of age, the Shenton line should be intact on all views of the hip; thereafter, any disruption of the Shenton line indicates an abnormality in the relation between the proximal femur and the acetabulum. As will be emphasized in the section on methods of treatment, this relation must be restored in order to prevent degenerative joint disease in later life (26, 45, 58, 63, 118).

Magnetic resonance imaging (MRI) has been used for DDH diagnosis and evaluation, as well as for documentation of femoral head-acetabular relationships after closed or open reduction (198, 199). With advances in software, this modality will no doubt provide useful information in the future, but the need for anesthesia in infants and children limits its utility (200, 201, 202 and 203).

The natural history of untreated DDH in the newborn is quite variable. Yamamuro and Doi followed up 52 patients whose hips had positive Ortolani signs for a 2-year period without treatment for the first 5 months. Of the 12 that they called “dislocated” hips, three (25%) were radiographically normal at 5 months of age. Of the 42 that they called “subluxable” hips, 24 (57%) were normal at 5 months (81).

Barlow reported that 1 of every 60 infants born has instability (i.e., positive Barlow sign) of one or both hips (87). More than 60% of these stabilize during the first week of life and 88% stabilize during the first 2 months without treatment. The remaining 12% become true congenital dislocations and persist in the absence of treatment. Pratt et al. did a follow-up, for an average of 11.2 years, of 18 “dysplastic” hips in patients who had been diagnosed on the basis of clinical and radiographic parameters at an age younger than 3 months. They found that 15 of these hips were radiographically normal (80).

Coleman followed up 23 untreated patients who had been diagnosed as having DDH on the basis of clinical and radiographic criteria at younger than 3 months. He found that 26% of the femoral heads became completely dislocated, 13% had partial contact of the femoral head with the acetabulum, 39% remained located but retained dysplastic features, and 22% were normal (48).

Most unstable hips in newborns stabilize soon after birth, some may go on to subluxation (partial contact of femoral head
with the acetabulum) or dislocation, and some may remain located (intact Shenton line) but retain anatomic dysplastic features. Because it is not possible to predict the outcome of unstable hips in newborns, all newborns with clinical hip instability, as manifested by a positive Ortolani or Barlow sign, should be treated.

In adults, the natural history of untreated complete dislocation varies and is affected by societal considerations (57, 66, 198, 199, 200 and 201). Despite complete dislocation, there may be little or no functional disability.

The natural history of complete dislocation depends on the presence or absence of two factors: a well-developed false acetabulum and bilaterality (27, 58, 67, 117, 204, 205). Wedge and Wasylenko demonstrated only a 24% chance of a good clinical outcome with a well-developed false acetabulum, but with a moderately developed or absent false acetabulum, the patients had a 52% chance of a good clinical outcome
(58, 67). Of 42 patients with complete dislocations, 13 had radiographically confirmed degenerative joint disease, such as loss of joint space, cyst formation, sclerosis, osteophyte formation, and flattening of the femoral head. Of these 13 patients, 10 (76%) had poor clinical outcomes.

Milgram reported the gross and histologic features of a case of bilateral DDH discovered at postmortem examination (206). This 74-year-old man had no hip or thigh pain and only mild backache for 5 years before his death. The femoral head had no articulation with any portion of the ilium and was covered with a thickened, markedly elongated hip joint capsule. The only degenerative changes were where the lesser trochanter abutted the overhanging superior acetabular rim. In the absence of a false acetabulum, most patients with complete dislocations do well, maintaining good range of motion with little functional disability (Fig. 23-20). Completely dislocated hips with well-developed false acetabula are more likely to develop radiographically visible degenerative joint disease changes and poor clinical outcomes (Fig. 23-21). Factors that lead to the formation or lack of formation of a false acetabulum remain unknown (26).

Back pain may occur in patients with bilateral dislocations. It is thought that this pain is secondary to the hyperlordosis of the lumbar spine that is associated with bilateral dislocations (26, 58, 67, 206, 207 and 208) (Melvin P, Johnston R, Ponseti IV, personal communication) (Fig. 23-22).

In unilateral complete dislocations, secondary problems of limb-length inequality, ipsilateral knee deformity and pain, scoliosis, and gait disturbance are common. Limblength inequalities of as much as 10 cm have been reported in patients with unilateral dislocations. These patients develop flexion-adduction deformities of the hip, which may lead to valgus deformities of the knee. The valgus knee deformity is often associated with attenuation of the medial collateral ligament and degenerative joint disease of the lateral compartment, although some medial compartment disease has also been described (26, 58, 67, 118, 205) (Melvin P, Johnston R, Ponseti IV, personal communication). The same factors that are involved in the development of secondary degenerative disease in the false acetabulum and in the associated clinical disability in bilateral cases affect unilateral dislocations also.

The natural history of dysplasia and subluxation in untreated patients is
important because of the likelihood that these findings can be extrapolated to residual dysplasia and subluxation after treatment (118, 204, 209, 210, 211, 212, 213 and 214).

After the neonatal period, the term dysplasia has an anatomic definition as well as a radiographic definition. Anatomic dysplasia refers to inadequate development of the acetabulum, the femoral head, or both (49). All subluxated hips (i.e., those in which there is some contact between the femoral head and the acetabulum) are by definition anatomically dysplastic. On film, the major difference between radiographic dysplasia and radiographic subluxation is determined by the integrity of the Shenton line. In radiographic subluxation, the Shenton line is disrupted and the femoral head is superiorly, laterally, or superolaterally displaced from the medial wall of the acetabulum. In radiographic dysplasia, the normal Shenton line relation is intact (58, 67, 215, 216) (Fig. 23-23). In the literature describing the natural history of DDH, these two radiographic and clinical entities are often not separated. Moreover, secondary degenerative changes may convert a radiographically dysplastic hip into a radiographically subluxated hip (206, 208, 212, 213, 216, 217 and 218) (Figs. 23-24 and 23-25).

Anatomic abnormalities are seen roentgenographically in subluxation and dysplasia, but the natural histories of these two radiographic entities are different. Residual radiographic subluxation after treatment of DDH invariably leads to degenerative joint disease and clinical disability (26, 66, 68, 118, 206, 211, 213, 216). The rate of deterioration is directly related to the severity of the subluxation and the age of the patient (213, 216).

There is considerable evidence that residual radiographic acetabular dysplasia leads to secondary degenerative joint disease, especially in women, although there are no predictive radiographic parameters (206, 212, 213, 216, 218, 219 and 220). The reasons for degenerative changes in radiographically dysplastic hips are probably mechanical in nature and related to increased contact stress over time. A certain threshold of “overpressure” (product of time and pressure, involving years of exposure to pressure above a 2-megapascal [MPa] level, leading to damage) (221, 222 and 223) may correlate with poor long-term outcome. Aspherical femoral heads (e.g., secondary to aseptic necrosis) tend to experience even more severe degrees of overpressure. It appears that radiographic degenerative joint disease correlates with the magnitude of the overpressure and the time of exposure (221). This overpressure may cause problems at a much younger age, with symptoms of “acetabular rim syndrome” (224) with associated labral tears, rim fractures and synovial cysts (225).

Physical signs of radiographic hip dysplasia may not be visible. Cases of radiographic hip dysplasia are diagnosed either only incidentally on the basis of radiographs taken for other reasons or after the patient develops symptoms (27, 28, 45, 77, 218). Stulberg and Harris found that 50% of their patients with radiographic dysplasia and degenerative joint disease had radiographic evidence of dysplasia in the other hip (218). Melvin et al., in their unpublished 30- to 50-year follow-up of DDH, demonstrated that 40% of the patients with DDH showed radiographic evidence of dysplasia in the opposite hip (Melvin P, Johnston R, Ponseti IV, personal communication) (225, 226 and 227). It has been estimated that 20% to 50% of degenerative joint disease of the hip is secondary to subluxation or residual radiographic acetabular dysplasia (45, 58, 216, 218, 219, 228, 229 and 230). Wiberg suggested that there was a direct correlation between the onset of radiographically determined degenerative joint disease and the amount of dysplasia as measured by the decrease in the CE angle (45) (Fig. 23-18).

Cooperman et al., in a radiographic study of degenerative joint disease and its relation to the severity of radiographic acetabular dysplasia, reviewed the 17 cases on which Wiberg based his conclusions (216). They concluded that 7 of 17 hips were actually subluxated. These subluxated hips were the most anatomically dysplastic; their CE angles averaged 2 degrees, and all seven had radiographically seen degenerative changes by the time the patients were 42 years of age. The other 10 hips in Wiberg’s series were radiographically dysplastic. They had intact Shenton lines and an average CE angle of 10 degrees. None of these patients developed radiographic degenerative joint disease before 39 years of age; however, degenerative changes became apparent radiographically by 57 years of age. In this review of Wiberg’s series, the decrease in CE angle was associated with an increase in anatomic acetabular dysplasia and an increased likelihood that the hip would be subluxated. Subluxation was the primary factor in the development of degenerative joint disease in this group. Subluxation predictably leads to degenerative joint disease and clinical disability over time.

Cooperman et al. described 32 hips (28 patients) with radiographic evidence of acetabular dysplasia (i.e., CE angle <20 degrees, but without subluxation and with the Shenton line intact), at an average follow-up of 22 years (216). All the patients eventually developed radiographic evidence of degenerative joint disease. However, there was no linear correlation between the CE angle and the rate of development of degenerative joint disease, as had been suggested previously by Wiberg. A decreased CE angle was associated solely with increasing radiographic evidence of acetabular dysplasia and not with subluxation, because patients with subluxation had been excluded in this series. Cooperman et al. demonstrated that radiographic evidence of acetabular dysplasia leads to radiographically detectable degenerative joint disease, but the process may take decades. This study also demonstrated that the conventional radiographic parameters used for describing dysplasia (e.g., CE angle, acetabular index of Sharp, percent coverage, depth, inclination) could not predict the rate at which a radiographically confirmed dysplastic hip joint would develop radiographic evidence of degenerative joint disease.

Stulberg and Harris demonstrated that there is no radiographic picture of degenerative joint disease that is uniquely associated with preexisting acetabular dysplasia (218). In 80% of patients with dysplasia, the CE angle is usually <20 degrees, but acetabular shallowness, as measured by acetabular depth, affects all of these patients. The investigators also demonstrated that the CE angle, the criterion most commonly used to quantitate dysplasia, could be affected by many factors, including positioning for the radiographs and the changes accompanying the normal development of degenerative joint disease. The secondary degenerative changes in a dysplastic acetabulum may give the hip a normal-appearing CE angle. In their series of 130 patients with primary or idiopathic degenerative joint disease, Stulberg and Harris were able to demonstrate that 48% showed evidence of primary acetabular dysplasia and that acetabular dysplasia frequently occurred in women with degenerative joint disease.

Additional evidence for the association between radiographic evidence of acetabular dysplasia and degenerative joint disease comes from the southern Chinese population. In an epidemiologic study from Hong Kong, where the incidence of childhood hip disease is low, the incidence of adult osteoarthritis (nontraumatic) was also shown to be low (54, 55).

Wedge and Wasylenko reported three peak periods of pain in subluxation, depending on the severity of the subluxation (58, 67). Patients with the most severe subluxation usually had the onset of symptoms during the second decade of life. Those with moderate subluxation presented during their third and fourth decades, and those with minimal subluxation usually experienced the onset of symptoms around the fifth decade.

Patients who present soon after the onset of symptoms rarely have the classic signs of degenerative joint disease such as decreased joint space, cyst formation, double acetabular floor, and inferomedial femoral head osteophytes. The only radiographic feature present at the onset of symptoms may be increased sclerosis in the weight-bearing area. This increased sclerosis is secondary to increasing osteoblastic stimulation in response to the decreased weight-bearing surface area; the increase of the normal per unit load strains the bone. The mechanism of pain in these instances is open to speculation.

In cases of subluxation, the mean age at onset of symptoms is 36.6 years in women and 54 years in men. Severe degenerative changes become evident radiographically approximately 10 years later by 46.4 years of age in women and 69.6 years of age in men.

Patients with subluxated hips usually experience onset of symptoms at a younger age than patients with complete dislocations do. After pain and radiographically evident degenerative disease start, the disease progresses rapidly. Harris reported that symptoms of degenerative joint disease associated with radiographic evidence of acetabular dysplasia occurred early in life and that almost 50% of the patients in his series with acetabular dysplasia had their first reconstructive procedure before 60 years of age, with fewer than 5% having their first reconstruction after 60 years of age (219).

At maturity, the ideal radiograph should have a well-developed teardrop, a normal femoral neck-shaft angle, an intact Shenton line, a downsloping sourcil, and a well-developed gothic arch (Fig. 23-26). Any deviation from this radiographic appearance may lead to degenerative joint disease over the long term (58, 118, 188, 212, 213, 216, 217 and 218)

One of the most controversial areas in the discussion of hip dysplasia either primary or as a residual of treatment is the effect of acetabular retroversion and/or femoral acetabular impingement (FAI) on the natural history or long-term outcome of patients.

There is increasing evidence that FAI may lead to acetabular cartilage delamination and degenerative joint disease (231, 232, 233, 234, 235, 236, 237 and 238) FAI is more commonly associated with a retroverted acetabulum which can be seen in cases of hip dysplasia (x-ray cross-over sign). Two types of impingement have been described: Cam and Pincer (Figs. 23-27 and 23-28) (239). While cam impingement may be determined by plane radiographs, particularly the lateral view with the hip in internal rotation, contrast-enhanced MRI is often used to gain a broader, more in-depth view of the anatomic abnormalities thought to be associated with FAI. Cam impingement results from deformities of the proximal part of the femur that may occur in patients with DDH particularly those treated late; while Pincer impingement generally is associated with acetabular overcoverage, both types may be present in the same patient (240, 241). While these anatomic findings are thought to be associated with degenerative joint disease, what is uncertain is the presence of these radiographic findings in the general population. Further studies will be necessary to clarify the incidence of retroversion and radiographic abnormalities of the proximal femur in the general population.