Developmental Dysplasia of the Hip


Background

The term congenital dislocation of the hip dates back to the time of Hippocrates. This condition, also known as hip dysplasia or developmental dysplasia of the hip (DDH), has been diagnosed and treated for several hundred years. Most notably, Ortolani, an Italian pediatrician in the early 1900s, evaluated, diagnosed, and began treating hip dysplasia. Galeazzi later reviewed more than 12,000 cases of DDH and reported the association between apparent shortening of the flexed femur and hip dislocation. Since then, significant progress has been made in the evaluation and treatment of DDH. [1, 2, 3, 4, 5]

The definition of DDH is not universally agreed upon. Typically, the term DDH is used in referring to patients who are born with dislocation or instability of the hip, which may then result in hip dysplasia. More broadly, DDH may be defined simply as abnormal growth of the hip. Abnormal development of the hip includes the osseous structures, such as the acetabulum and the proximal femur, as well as the labrum, capsule, and other soft tissues. This condition may occur at any time, from conception to skeletal maturity. The author prefers to use the term hip dysplasia, considering it both simpler and more accurate. Internationally, this disorder is still referred to as congenital dislocation of the hip.

More specific terms are often used to describe the condition more precisely; these are defined as follows:

  • Subluxation – Incomplete contact between the articular surfaces of the femoral head and acetabulum
  • Dislocation – Complete loss of contact between the articular surface of the femoral head and acetabulum
  • Instability – Ability to subluxate or dislocate the hip with passive manipulation
  • Teratologic dislocation – Antenatal dislocation of the hip

Early diagnosis is the most crucial aspect of the treatment of children with DDH. The use of ultrasonography and other diagnostic imaging modalities and the implementation of improved educational programs will most likely decrease the number of children with DDH who are diagnosed late. Newer, less invasive surgical techniques (eg, endoscopic techniques and image-guided surgery) are being developed in an effort to decrease the morbidity of surgery and to ease recovery.

Anatomy

The normal growth of the acetabulum depends on normal epiphyseal growth of the triradiate cartilage and on the three ossification centers located within the acetabular portion of the pubis (os acetabulum), ilium (acetabular epiphysis), and ischium. Additionally, normal growth of the acetabulum depends on normal interstitial appositional growth within the acetabulum. The presence of the spherical femoral head within the acetabulum is critical for stimulating normal development of the acetabulum.

The anatomy of the dislocated hip, especially after several months, often includes formation of a ridge called the neolimbus. Closed reduction is often unsuccessful at a later date, secondary to various obstacles to reduction. These include adductor and psoas tendon contraction, ligamentous teres, a transverse acetabular ligament, and pulvinar and capsular constriction. With long-standing dislocations, interposition of the labrum can also interfere with reduction.

Pathophysiology

DDH involves abnormal growth of the hip. Ligamentous laxity is also believed to be associated with hip dysplasia, though this association is less clear. DDH is not part of the classic description of disorders that are associated with significant ligamentous laxity, such as Ehlers-Danlos syndrome or Marfan syndrome.

Children often have ligamentous laxity at birth, yet their hips are not usually unstable; in fact, it takes a great deal of effort to dislocate a child's hip. Therefore, more than just ligamentous laxity may be required to result in DDH. At birth, white children tend to have a shallow acetabulum. [67; this may provide a susceptible period in which abnormal positioning or a brief period of ligamentous laxity may result in hip instability. However, this characteristic is not as true for children of African descent, who have a lower rate of DDH. [8]

Etiology

The etiology of hip dysplasia is not clear, but this condition does appear to be related to a number of different factors. [9One such factor is racial background: In Native Americans and Laplanders, the prevalence of hip dysplasia is much higher (nearly 25-50 cases per 1000 persons) than in other races, and the prevalence is very low in southern Chinese and black populations. [1011128An underlying genetic disposition also appears to exist, in that the frequency of hip dysplasia is 10 times higher in children whose parents had DDH than in those whose parents did not. [13]

Other factors possibly related to DDH include intrauterine positioning and sex, and some of these are interrelated. Female sex, being the first-born child, and breech positioning are all associated with an increased prevalence of DDH. An estimated 80% of persons with DDH are female, [14and the rate of breech positioning in children with DDH is approximately 20% (compared with 2-4% in the general population). [1516The prevalence of DDH in females born in breech position has been estimated to be as high as 1 case in 15 persons in some studies. [17]

Other musculoskeletal disorders of intrauterine malpositioning or crowding, such as metatarsus adductus and torticollis, have been reported to be associated with DDH. [1819Oligohydramnios is also reported to be associated with an increased prevalence of DDH. [20The left hip is more commonly associated with DDH than the right hip, possibly because of the common intrauterine position of the left hip against the mother's sacrum, which forces it into an adducted position. [20Children in cultures in which the mother swaddles the baby, forcing the infant's hips to be adducted, also have a higher rate of hip dysplasia. [21]

Hip dysplasia can be associated with underlying neuromuscular disorders, such as cerebral palsymyelomeningocelearthrogryposis, and Larsen syndrome, though such cases are not usually considered DDH.

Epidemiology

The overall frequency of DDH is usually reported as approximately 1 case per 1000 individuals, though Barlow believed that the incidence of hip instability during newborn examinations was as high as 1 case per 60 newborns. [22According to Barlow's study, more than 60% of newborns with hip instability became stable by age 1 week, and 88% became stable by age 2 months, leaving only 12% (of the 1 in 60 newborns, or 0.2% overall) with residual hip instability.

Prognosis

Overall, the prognosis for children treated for hip dysplasia is very good, especially if the dysplasia is managed with closed treatment. If closed treatment is unsuccessful and open reduction is needed, the outcome may be less favorable [23, although the short-term outcome appears to be satisfactory. If secondary procedures are needed to obtain reduction, then the overall outcome is significantly worse.

Some authors believe that patients with bilateral hip dysplasia have a poorer prognosis because of frequent delays in diagnosis and greater treatment requirements. [2425In a study comparing the outcomes of walking-age children with bilateral hip dislocations who underwent open reduction and pelvic osteotomy with or without femoral osteotomy with those of walking-age children with unilateral dislocated hips who underwent the same set of procedures, the radiographic outcomes were similar. [26]

In this study, the rate of osteonecrosis was higher in the bilateral group, but this difference was explained by older age at surgery and a greater degree of hip dislocation before surgery. [26The authors concluded that the clinical outcomes after surgery of the children with bilateral hip dislocations were worse mainly because of asymmetric outcomes.


Physical Examination

Early clinical manifestations of developmental dysplasia of the hip (DDH) are identified during examination of the newborn. The classic examination finding is revealed with the Ortolani maneuver, in which a palpable "clunk" is present when the hip is directed in and out of the acetabulum and over the neolimbus. A high-pitched "click" (as opposed to a clunk) in all likelihood has little association with acetabular pathology. [2728Ortolani originally described this clunk as occurring with either subluxation or reduction of the hip (in or out of the acetabulum). More commonly, the Ortolani sign is referred to as a clunk felt when the hip reduces into the acetabulum, with the hip in abduction.

To perform this maneuver correctly, the patient must be relaxed. Only one hip is examined at a time. The examiner's thumb is placed over the patient's inner thigh, and the index finger is gently placed over the greater trochanter. The hip is abducted, and gentle pressure is placed over the greater trochanter. In the presence of DDH, a "clunk," similar to that noted in turning a light switch on or off, is felt when the hip is reduced. The Ortolani maneuver should be performed gently, in such a way that the fingertips do not blanch. [29]

Barlow described another test for DDH that is performed with the hips in an adducted position, in which slight gentle posterior pressure is applied to the hips. A "clunk" should be felt as the hip subluxates out of the acetabulum. [22]

The clinical examination for late DDH (age 3-6 months) is quite different. At this point, the hip, if dislocated, is often dislocated in a fixed position. [13The Galeazzi sign is a classic identifier of unilateral hip dislocation (see the image below). This is performed with the patient lying supine and the hips and knees flexed. The examination should demonstrate that one leg appears shorter than the other. Although this finding is usually due to hip dislocation, it is important to realize that any limb-length discrepancy results in a positive Galeazzi sign.

Galeazzi sign is classic identifier of unilateral Galeazzi sign is classic identifier of unilateral hip dislocation. Patient lies supine, with hips and knees flexed. Examination should demonstrate that one leg appears shorter than other. Although this appearance is usually due to hip dislocation, it is important to realize that any limb-length discrepancy results in positive Galeazzi sign.

Additional physical examination findings for late dislocation include asymmetry of the gluteal thigh or labral skin folds, decreased abduction on the affected side, standing or walking with external rotation, and leg-length inequality. [30]

Bilateral dislocation of the hip, especially at a later age, can be quite difficult to diagnose. This condition often manifests as a waddling gait with hyperlordosis. Many of the aforementioned clues suggesting a unilateral dislocated hip are absent, such as the Galeazzi sign, asymmetric thigh and skin folds, or asymmetrically decreased abduction. Careful examination is needed, and a high level of suspicion is important.

Any limp in a child should be considered abnormal. The diagnosis can be quite variable, but an underlying etiology must always be pursued.

Of primary importance is making the diagnosis of hip dislocation or dysplasia. Once this diagnosis is made, the patient should be examined to make sure that there is no underlying medical or neuromuscular disorder. Proximal femoral focal deficiency can masquerade as hip dysplasia and often manifests similarly. Because the femoral head does not ossify, the radiographic appearance also may be deceiving. Other neuromuscular disorders can manifest as dysplasia later in life, such as Charcot-Marie-Tooth disease.

Using expected-value decision analysis, Mahan et al found that the screening strategy associated with the highest probability of having a nonarthritic hip at the age of 60 years was to screen all neonates for hip dysplasia with a physical examination and to use ultrasonography selectively for high-risk infants. [31The expected value of a favorable hip outcome was 0.9590 for screening all neonates with physical examination and selective use of ultrasonography, 0.9586 for screening all neonates with physical examination and ultrasonography, and 0.9578 for no screening.

Complications

Numerous possible complications can occur, including redislocation, stiffness of the hip, infection, blood loss, and, possibly the most devastating, avascular necrosis of the femoral head. The rate of femoral head necrosis varies substantially; depending on the study, it may be anywhere from 0% to 73%. Numerous studies demonstrate that extreme abduction, especially when combined with extension and internal rotation, results in a higher rate of avascular necrosis.


Ultrasonography

Ultrasonography has been of substantial benefit in the assessment and treatment of children with developmental dysplasia of the hip (DDH). [353637The benefit of screening all children with ultrasonography is controversial. [3839Even with ultrasonographic screening, children with hip dysplasia can be diagnosed late, and one concern with routine ultrasonographic evaluation of newborns is overdiagnosis of hip dysplasia (ie, increased false-positive results). [40]

The use of ultrasonography for only high-risk infants has not yet been shown to reduce the prevalence of late diagnosis of hip dysplasia. [41However, most authors agree that it is an excellent tool for assessing children with suspected hip instability and a useful aid in the treatment of children with DDH, especially in monitoring reduction by closed methods. [42]

An ultrasound evaluation is typically performed either by assessing the alpha and beta angles or by performing a dynamic evaluation. [353743An alpha angle outlines the slope of the superior aspect of the bony acetabulum, with an angle greater than 60º considered normal. The beta angle, which is considered normal if less than 55º, depicts the cartilaginous component of the acetabulum. Many institutions now use a dynamic form of ultrasonography, as heralded by Harcke. [42]

Plain Radiography

Standard radiographic views for DDH include a standing anteroposterior (AP) view of the pelvis, with the hips in neutral position, and a false profile view in which the patient is standing angled at 65º from the x-ray plate. The radiograph is then taken, profiling the anterior aspect of the acetabulum. If any evidence of hip subluxation is present, an abducted internal rotation view can help determine if the hip reduces and better determines the true neck-shaft angle of the proximal femur.

Radiographic evaluation is typically carried out as follows (see the image below). From an AP radiograph of the hips, a horizontal line (Hilgenreiner line) is drawn between each triradiate cartilage. Next, lines perpendicular to the Hilgenreiner line are drawn through the superolateral edge of the acetabulum (Perkin lines), dividing the hip into four quadrants. The proximal medial femur should be in the lower medial quadrant, or the ossific nucleus of the femoral head, if present (usually observed in patients aged 4-7 months), should be in the lower medial quadrant.

Typical radiographic evaluation of developmental dTypical radiographic evaluation of developmental dysplasia of hip (DDH). From anteroposterior radiograph of hips, horizontal line (Hilgenreiner line) is drawn between each triradiate cartilage. Next, lines are drawn perpendicular to Hilgenreiner line through superolateral edge of acetabulum (Perkin line), dividing hip into 4 quadrants. Proximal medial femur should be in lower medial quadrant, or ossific nucleus of femoral head, if present (usually observed in patients aged 4-7 months), should be in lower medial quadrant. Acetabular index is angle between Hilgenreiner line and line drawn from triradiate cartilage to lateral edge of acetabulum. Typically, this angle decreases with age and should measure less than 20° by 2 years of age. Shenton line is drawn from medial aspect of femoral neck to inferior border of pubic rami. It should create smooth arc that is not disrupted. Disruption of Shenton line indicates presence of some degree of hip subluxation.

Additionally, the acetabular indices can be measured. These refer to the angle between the Hilgenreiner line and a line drawn from the triradiate cartilage to the lateral edge of the acetabulum. Typically, the angle decreases with age and should measure less than 20º by the time the child is aged 2 years. [4445]

The Shenton line — a line drawn from the medial aspect of the femoral neck to the inferior boarder of the pubic rami — can also be evaluated. This line should create a smooth arc that is not disrupted. Disruption of the Shenton line indicates the presence of some degree of hip subluxation.

CT and MRI

Computed tomography (CT) can also be helpful in determining femoral anteversion and in determining the extent of posterior acetabular coverage. Three-dimensional (3D) images are also quite popular and can be beneficial in visualizing the overall shape of the acetabulum.

Magnetic resonance imaging (MRI) can be beneficial in identifying the underlying bony and soft-tissue anatomy. One study evaluated MRI findings in pediatric orthopedic patients who showed residual subluxation after reduction of DDH. [46Twenty-two subjects were followed conservatively, and 14 subjects underwent corrective surgery.

The subjects in the surgery arm of the study showed the presence of a high-signal intensity area (HSIA) within the weight-bearing portion of the acetabular cartilage preoperatively, which decreased or disappeared after the surgical procedure. [46In the conservative arm, those with HSIAs demonstrated poor acetabular growth and those without HISAs showed acetabular growth. The researchers concluded that HSIAs on MRI may be a marker for poor acetabular growth, which would make these areas valuable findings in corrective surgery decision-making.

A retrospective review compared CT with MRI in the evaluation of hip reduction in patients younger than 13 months with hip dysplasia. [47The results indicated that whereas MRI was a viable alternative to CT, CT required significantly less scan time than MRI did and cost less. However, CT was slightly less specific than MRI was. [47]

Arthrography

Arthrography is a dynamic study, performed by injecting radiopaque dye into the hip joint and then carrying out a fluoroscopic examination, usually with the patient under anesthesia. Although it can be performed independently, it is routinely performed in conjunction with a closed reduction. Arthrography can be helpful in determining the underlying cartilaginous profile and dynamic stability of the hip. [36It has also been used in conjunction with a hip MRI study to facilitate demonstration of labral tears.

When arthrography is performed in combination with a closed reduction, the adequacy of the reduction can be assessed. Increased medial joint space, as demonstrated by medial pooling of the dye and a rounded or interposing limbus, may be indicative of poor long-term results. After closed reduction and immobilization in a hip spica cast, a limited CT scan in the transverse plane is obtained to ensure the hip is not subluxated or dislocated posteriorly.



Ultrasonography

Ultrasonography has been of substantial benefit in the assessment and treatment of children with developmental dysplasia of the hip (DDH). [353637The benefit of screening all children with ultrasonography is controversial. [3839Even with ultrasonographic screening, children with hip dysplasia can be diagnosed late, and one concern with routine ultrasonographic evaluation of newborns is overdiagnosis of hip dysplasia (ie, increased false-positive results). [40]

The use of ultrasonography for only high-risk infants has not yet been shown to reduce the prevalence of late diagnosis of hip dysplasia. [41However, most authors agree that it is an excellent tool for assessing children with suspected hip instability and a useful aid in the treatment of children with DDH, especially in monitoring reduction by closed methods. [42]

An ultrasound evaluation is typically performed either by assessing the alpha and beta angles or by performing a dynamic evaluation. [353743An alpha angle outlines the slope of the superior aspect of the bony acetabulum, with an angle greater than 60º considered normal. The beta angle, which is considered normal if less than 55º, depicts the cartilaginous component of the acetabulum. Many institutions now use a dynamic form of ultrasonography, as heralded by Harcke. [42]

Plain Radiography

Standard radiographic views for DDH include a standing anteroposterior (AP) view of the pelvis, with the hips in neutral position, and a false profile view in which the patient is standing angled at 65º from the x-ray plate. The radiograph is then taken, profiling the anterior aspect of the acetabulum. If any evidence of hip subluxation is present, an abducted internal rotation view can help determine if the hip reduces and better determines the true neck-shaft angle of the proximal femur.

Radiographic evaluation is typically carried out as follows (see the image below). From an AP radiograph of the hips, a horizontal line (Hilgenreiner line) is drawn between each triradiate cartilage. Next, lines perpendicular to the Hilgenreiner line are drawn through the superolateral edge of the acetabulum (Perkin lines), dividing the hip into four quadrants. The proximal medial femur should be in the lower medial quadrant, or the ossific nucleus of the femoral head, if present (usually observed in patients aged 4-7 months), should be in the lower medial quadrant.

Typical radiographic evaluation of developmental dTypical radiographic evaluation of developmental dysplasia of hip (DDH). From anteroposterior radiograph of hips, horizontal line (Hilgenreiner line) is drawn between each triradiate cartilage. Next, lines are drawn perpendicular to Hilgenreiner line through superolateral edge of acetabulum (Perkin line), dividing hip into 4 quadrants. Proximal medial femur should be in lower medial quadrant, or ossific nucleus of femoral head, if present (usually observed in patients aged 4-7 months), should be in lower medial quadrant. Acetabular index is angle between Hilgenreiner line and line drawn from triradiate cartilage to lateral edge of acetabulum. Typically, this angle decreases with age and should measure less than 20° by 2 years of age. Shenton line is drawn from medial aspect of femoral neck to inferior border of pubic rami. It should create smooth arc that is not disrupted. Disruption of Shenton line indicates presence of some degree of hip subluxation.

Additionally, the acetabular indices can be measured. These refer to the angle between the Hilgenreiner line and a line drawn from the triradiate cartilage to the lateral edge of the acetabulum. Typically, the angle decreases with age and should measure less than 20º by the time the child is aged 2 years. [4445]

The Shenton line — a line drawn from the medial aspect of the femoral neck to the inferior boarder of the pubic rami — can also be evaluated. This line should create a smooth arc that is not disrupted. Disruption of the Shenton line indicates the presence of some degree of hip subluxation.

CT and MRI

Computed tomography (CT) can also be helpful in determining femoral anteversion and in determining the extent of posterior acetabular coverage. Three-dimensional (3D) images are also quite popular and can be beneficial in visualizing the overall shape of the acetabulum.

Magnetic resonance imaging (MRI) can be beneficial in identifying the underlying bony and soft-tissue anatomy. One study evaluated MRI findings in pediatric orthopedic patients who showed residual subluxation after reduction of DDH. [46Twenty-two subjects were followed conservatively, and 14 subjects underwent corrective surgery.

The subjects in the surgery arm of the study showed the presence of a high-signal intensity area (HSIA) within the weight-bearing portion of the acetabular cartilage preoperatively, which decreased or disappeared after the surgical procedure. [46In the conservative arm, those with HSIAs demonstrated poor acetabular growth and those without HISAs showed acetabular growth. The researchers concluded that HSIAs on MRI may be a marker for poor acetabular growth, which would make these areas valuable findings in corrective surgery decision-making.

A retrospective review compared CT with MRI in the evaluation of hip reduction in patients younger than 13 months with hip dysplasia. [47The results indicated that whereas MRI was a viable alternative to CT, CT required significantly less scan time than MRI did and cost less. However, CT was slightly less specific than MRI was. [47]

Arthrography

Arthrography is a dynamic study, performed by injecting radiopaque dye into the hip joint and then carrying out a fluoroscopic examination, usually with the patient under anesthesia. Although it can be performed independently, it is routinely performed in conjunction with a closed reduction. Arthrography can be helpful in determining the underlying cartilaginous profile and dynamic stability of the hip. [36It has also been used in conjunction with a hip MRI study to facilitate demonstration of labral tears.

When arthrography is performed in combination with a closed reduction, the adequacy of the reduction can be assessed. Increased medial joint space, as demonstrated by medial pooling of the dye and a rounded or interposing limbus, may be indicative of poor long-term results. After closed reduction and immobilization in a hip spica cast, a limited CT scan in the transverse plane is obtained to ensure the hip is not subluxated or dislocated posteriorly.



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