AUTHOR AND EDITOR INFORMATION

Section 1 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

INTRODUCTION

Section 2 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Background

Developmental dysplasia of the hip (DDH) is a spectrum of disorders affecting the proximal femur and acetabulum that leads to hip subluxation and dislocation. Early diagnosis and treatment is important because failure to diagnose DDH in neonates and young infants can result in significant morbidity.¹

Related eMedicine topics:
Developmental Dysplasia of the Hip (Orthopedic Surgery)
Dislocation, Hip

Related Medscape topics:
Case Q&A: Developmental Dysplasia of the Hip, Part I-Diagnosis
Case Q&A: Developmental Dysplasia of the Hip, Part II-Treatment
Resource Center  Neonatal Medicine
Resource Center  Joint Disorders

Pathophysiology

DDH is the result of a disruption in the normal relationship between the acetabulum and femoral head. Without adequate contact between them, neither develops normally. At birth, the acetabulum has small bony and large cartilaginous contents, and the percentage of the femoral head covered by the acetabulum is smaller than it is at any other time in development; therefore, the first 6 weeks of an infant's life are critical to healthy hip joint formation.^{2, 3}

Frequency

United States

DDH occurs in approximately 1.5% of neonates.

International

Because of genetic susceptibility and differences in medical care and diagnosis, the reported incidence of DDH varies throughout the world. Worldwide, DDH occurs in approximately 1% of all neonates. The incidence increases in colder climates; this is believed to be the result of tight swaddling of the infant with the legs in hyperextension.

The risk factors for DDH include female sex; a familial history (children of a parent who had DDH have a 12% risk, and subsequent siblings of a child with DDH have a 6% risk); breech presentation; multiple gestation; first pregnancy; high birth weight; oligohydramnios; and postural and nonpostural abnormalities, including clubfoot deformity and congenital torticollis. It should be noted, however, that most cases of DDH occur in infants without identified risk factors.^{4, 5, 6, 7}

The left hip is affected 3 times more often than the right hip. This difference is possibly related to the left occiput anterior position of most neonates, which may limit abduction of the left hip as it lies against the mother's spine.

Mortality/Morbidity

The failure to diagnose and treat DDH in the immediate neonatal period can result in significant morbidity, including closed treatment failure, the need for open reduction, and the eventual development of osteoarthritis.

Possible complications of treatment include persistent dysplasia, recurrent dislocation, and, most significantly, avascular necrosis of the femoral head.

Race

DDH is more common in white neonates than in African American, Korean, or Chinese neonates. The incidence of DDH in Lapp infants, as well as in indigenous North American groups, is high. This observation may be related to the traditional methods that these groups use to carry their young (for example, some cultures use papooses, which keep the infants' legs in adduction).

Sex

DDH is 4-8 times more common in female infants than in male infants. This difference is believed to be the result of the increased levels of circulating estrogens and relaxin at the time of birth and an increased susceptibility to them. These hormones cause a generalized ligamentous laxity.⁴

Age

Two types of dislocations occur: teratologic and typical.

Most cases of DDH involve typical dislocations. They occur in neurologically intact infants in the perinatal period and, therefore, are developmental.

Teratologic dislocations occur in infants with underlying neuromuscular disorders, such as myelodysplasia and arthrogryposis. Teratologic dislocations occur in utero and, therefore, are truly congenital.

Anatomy

The normal hip develops from a single block of cartilage that separates into femoral and acetabular components at 7-8 weeks of gestation. The characteristic shape of the hip is a result of reciprocal contact between the acetabulum and the femur during growth. At birth, the acetabulum has a small bony component and a larger cartilaginous component. During the first 6 postnatal weeks, the acetabulum is particularly susceptible to modeling. If the femoral head is in the normal position in the acetabulum, a normal hip results. If the femoral head is in an abnormal position that is not corrected, the result may be a dysplastic hip.

Clinical Details

Physical examination is an important method for diagnosing DDH, and it is part of the routine clinical evaluation of the neonate. The Barlow maneuver is used to determine if a hip is dislocatable. The femur is flexed and adducted while posteriorly-directed pressure is applied. This maneuver displaces an unstable hip from the acetabulum.

The Ortolani maneuver is used to reduce a dislocated hip. This is performed by abducting and flexing the femur; a palpable low-frequency "clunk" is noted as the femoral head slides back and reduces into the acetabulum. Hip "clicks" are benign findings that are palpable and have higher-frequency noises; they result from stretching and snapping of the joint capsule and tendons.

As infants mature, capsule laxity decreases and muscle tightness increases, diminishing the sensitivity of the Ortolani and Barlow maneuvers. The Allis, or Galeazzi, sign is an asymmetry of the skin folds caused by an apparent shortening of the thigh. This is best noted by comparing the lengths of the 2 flexed thighs when they are held together.

The goal of treatment is to restore contact between the femoral head and the acetabulum. Treatment varies with the patient's age and the degree of instability. In neonates, most unstable hips normalize spontaneously within the first 2-4 weeks after birth; therefore, observation and reexamination when the neonate is aged 3-4 weeks is most commonly recommended for subluxatable hips in the immediate neonatal period.

The initial treatment for DDH involves the use of a brace that maintains the hip in flexion and abduction. The brace is worn until the clinical and radiologic examination findings are normal. Children older than 6 months usually are too large to tolerate a brace. Closed reduction under general anesthesia is usually attempted first. The reduction can be evaluated with magnetic resonance imaging (MRI) or an arthrogram and a postreduction computed tomography (CT) scan. If reduction is successful, the hip is held in a spica cast for several months. If it is unsuccessful, open reduction can be performed. If the diagnosis is made after deformity of the bones has occurred (usually in children older than 2 years), femoral or pelvic osteotomy and open reduction may be performed.

Preferred Examination

Ultrasonography (US) is the preferred modality for evaluating the hip in infants who are 6 months or younger. US enables direct imaging of the cartilaginous portions of the hip that cannot be seen on plain radiographs.⁸ Furthermore, US enables dynamic study of the hip with stress maneuvering. Practically speaking, the examination can often be successfully performed after 6 months of age (even up to 10-12 months) depending upon the degree of ossification of the capital femoral epiphysis. An attempt at US examination is suggested, to limit the neonates exposure to ionizing radiation. If unsuccessful, plain films can follow.

An Austrian orthopedist, Professor Reinhard Graf, first introduced US examination of the hip in 1980.² His technique included the calculation of numerous angles, a complicated classification system of hip subtypes, and the orientation of the B-mode images so that all hips were displayed on right coronal projections. Proponents of static scanning cite that it is fast, easy to perform, and reproducible. Widespread usage in Western Europe has reduced the incidence of undetected DDH requiring open reduction to the lowest in the world.^{9, 10}

With the advent of real-time US in 1984, Dr. H. Theodore Harcke and associates at the DuPont Institute in Wilmington, Delaware, introduced a dynamic approach to studying the hips. Dr. Harcke is the principal drafter of the American College of Radiology (ACR) standard, and his dynamic approach is predominantly used in US examination.^{8, 11}

The capital femoral epiphyses begin to ossify when an infant is aged 2-8 months. As the size of the ossification centers enlarge, shadowing may obscure the deeper acetabulum and limit US examination. Plain radiography then becomes the preferred modality for evaluating the hip. Plain radiographs are typically obtained in the frontal pelvis, with the legs in the neutral position. If the hips are displaced or dysplastic, a second view may be obtained, with the hips in flexion and external rotation (ie, the frog-leg position) to look for reduction. The gonads of male patients should be shielded whenever possible.^{12, 13, 14, 15, 16}

Limitations of Techniques

Dynamic US examination is operator-dependent, and it requires training and experience for confident evaluation of the infant hip. Also, because US is highly sensitive in hip imaging, minor abnormalities or normal early laxities may be revealed. This is especially true of static imaging alone. Some abnormalities detected by US may not be clinically significant, but they may be mistakenly overdiagnosed and overtreated.

DIFFERENTIALS

Section 3 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Other Problems to Be Considered

Traumatic hemarthrosis
Congenital coxa vara
Cerebral palsy - Incomplete femoral head coverage as a result of developmentally smaller but normally shaped acetabulum
Abnormal joint laxity - Down syndrome, Ehlers-Danlos syndrome, familial joint laxity
Tight hip adductors

RADIOGRAPH

Section 4 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Findings

Plain radiographs of the pelvis are most helpful when significant ossification of the capital femoral epiphyses has occurred and when adequate US evaluation cannot be performed. Plain radiographs of the pelvis are obtained in the frontal projection with the legs in the neutral position. Before the femoral heads begin to ossify, the projected locations must be estimated.

Line measurements made on the anteroposterior radiograph help in determining the relationship of the femoral head with the acetabulum (see Image 1).

• The acetabular angle is determined by first drawing the Hilgenreiner (or Y-Y) line, which is a horizontal line between the 2 triradiate or Y-Y cartilages, and then drawing a second line connecting the superolateral and inferomedial margins of the acetabular roof, as Kirks and Griscom reported.¹³ The normal acetabular angle is approximately 28° at birth. The angle decreases gradually with age as a result of modeling of the acetabulum by the femoral head and of the maturation of developing bone along the superolateral acetabular roof. The acetabular angle is often increased in DDH because maturation and ossification of the acetabulum are abnormal and delayed.
• The Perkins line is drawn at the outer acetabular margin and is perpendicular to the Hilgenreiner line. These lines divide the hip into quadrants. The unossified femoral head normally is centered in the inferomedial quadrant (see Image 2).
• In the normal hip, the Shenton line is a smooth unbroken arc that bridges the medial femoral metaphysis and the inferior edge of the superior pubic ramus. Displacement of the femoral head out of the joint space and disruption of the Shenton line are suggestive of DDH.

Delayed ossification of the femoral epiphysis is observed in the unstable hip. A false acetabulum eventually develops secondary to molding of the displaced ossification center against the bony pelvis (see Image 3).

To assess reducibility, a frontal view of the pelvis can be obtained with the legs in external rotation (ie, frog-leg position; see Image 4).

Degree of Confidence

Plain radiography has a low sensitivity, exposes the infant to ionizing radiation, and does not provide dynamic information. Radiographs are difficult to interpret before the capital femoral epiphyses ossify.

False Positives/Negatives

Because some hips may be subluxatable but not frankly dislocated or dislocatable only with Barlow maneuvers, plain radiographs obtained in neonates or infants with their hips in the neutral position frequently fail to depict DDH.

CT SCAN

Section 5 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Findings

CT is useful for evaluating complicated dislocations and for postoperative evaluation of the hip. CT can depict osseous blocks to relocation, as well as iliopsoas tendon capsule constriction, a thick ligamentum teres, and fibrofatty pulvinar hypertrophy. CT can also be used to evaluate femoral and acetabular anteversion.¹⁴

In infants with spica casts, low-milliamperage selective thin-section CT sections can confidently and quickly assess concentric reduction before the patient is discharged.

MRI

Section 6 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Findings

MRI can be useful in the preoperative and postoperative evaluation of a hip with many complications. MRI can be used to distinguish the labrum, capsule, and acetabular cartilage. MRI is useful for detecting the complications of DDH and treatment for DDH, such as avascular necrosis of the femoral head and joint effusions. MRI can also be used to demonstrate iliopsoas tendon compression, a thick ligamentum teres, and pulvinar hypertrophy.¹⁴

ULTRASOUND

Section 7 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Findings

ACR standard US examination⁸ of the infant hip is performed in 2 planes, the coronal (see Image 5) and transverse (see Image 6), as follows:

• A high-resolution linear array transducer must be used.
• The infant may be examined in the supine or lateral decubitus position, with the hip in a 90º flexed position.
• The operator uses one hand to hold the infant's knee at a right angle to the thigh. The palm of an open hand may be placed on the small of the infant's back.
• The thigh is held in the neutral position for imaging.

The unossified cartilaginous femoral head appears as a speckled ball in the acetabular fossa. Once ossification begins, it appears as a central area of increased echogenicity in the center of the cartilaginous head.

The femoral head should be centered in the joint space, with half or more of the femoral head medial to the baseline in the coronal plane. The extent of maturity of the acetabulum can also be quantified by using angular measurements (see Image 7). The ACR considers the calculation of these measurements optional. The standard coronal sectioning plane must be used at the deepest portion of the acetabulum, where the ilium appears as a straight line, perpendicular to the femoral head and parallel to the surface of the transducer.

Acetabular maturity

To quantify acetabular maturity, alpha and beta angles are determined by the application of 3 lines drawn in the standard coronal plane (see Image 8). The baseline passes through the plane of the ilium, where it connects to the osseous acetabular convexity. The inclination line passes from the lateral end of the acetabulum to the labrum, parallel to the cartilaginous roof. The roofline passes along the plane of the bony acetabular convexity.

• The alpha angle is used most commonly as a measurement of acetabular concavity, and it is calculated as the angle between the baseline and the roofline. A normal alpha angle is 60º or greater. Angles of 50-60º may be physiologically typical in the immediate neonatal period, but hips with these angles are considered immature and require clinical and US follow-up. Angles of less than 50º are always considered abnormal and require treatment.
• The beta angle is measured between the baseline and the inclination line. It indicates the acetabular cartilaginous roof coverage. An angle of less than 55º is considered normal. The smaller the angle, the less the cartilaginous coverage and the better the bony acetabular coverage of the femoral head.
• Not all dynamic hip imagers use these angles for the diagnosis and care of babies with DDH. Many use descriptive terms instead of numbers.

In a complementary method of assessing acetabular development, the distance between the medial aspect of the femoral head and the baseline (d) is compared with the maximum diameter of the femoral head (D); this d/D ratio is expressed as a percentage. This ratio represents the coverage of the femoral head by the bony acetabulum in the standard coronal plane (see Image 9). Coverage of 58% or greater is considered normal. The smaller the coverage, the greater the acetabular immaturity.

Stress maneuvering (ie, the Barlow maneuver) with the femur in 90º of flexion and maximum adduction is performed during transverse imaging to assess stability (see Images 10-11). The use of stress is optional in coronal imaging, which may be performed with the patient's leg in a flexed or neutral position. Stress is omitted if the infant is receiving treatment for DDH with a Pavlik harness. Stress maneuvering reveals instability, subluxation (see Image 12), or dislocation (see Image 13). In dislocated hips, the Ortolani maneuver should be performed to check for reducibility.

An ancillary sign of instability is asymmetry in the degree of ossification of the femoral heads.

Degree of Confidence

Some experience is helpful in assessing hip stability because some laxity is normal in the infant's first months of life. Not all sonographically abnormal hips need treatment because spontaneous normalization is common in some infants by the time they are aged 4 weeks; therefore, the decision to treat is based not only on sonographic findings but also on clinical findings. Because many unstable hips may spontaneously normalize within the first 2 weeks of a neonate's life, delaying the first US study for 2 weeks should be considered.¹⁵

False Positives/Negatives

Mild instability may be observed in healthy neonates in their first few days of life, when the typical femoral head has a laxity of 3-4 mm on average. This amount of motion should resolve spontaneously within the first months of an infant's life, after maternal hormonal influences diminish.

Inexperienced US examiners can mistake the greater trochanter cartilage for the femoral head and incorrectly diagnose DDH.

It has been suggested that, because US is very sensitive, a plain radiograph be performed to confirm DDH in infants over the age of 4 months with abnormal static US examinations, as ossification of the capital femoral epiphyses would begin to be present, thereby limiting over-treatment. This unnecessary exposure to ionizing radiation, however, can be avoided by the performance of a dynamic US examination.^{15, 16}

INTERVENTION

Section 8 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Arthrography can be performed to assess the dislocated hip; often, it is performed at the time of surgical reduction, particularly if the reduction appears to be difficult to maintain. The indications for arthrography are fewer with the development of better sonography, the advent of MRI, and the availability to confirm reductions in spica casts with CT scanning.¹⁷

Medical/Legal Pitfalls

• In some Western nations, routine screening of all neonates is not performed. Mass screening is not performed in the United States, where only children with abnormal clinical examination findings or those with identified risk factors are examined.
• Failure to treat clinically insignificant minor abnormalities detected on early US examination may have legal implications in a litigious society; however, the treatment of minor abnormalities that are likely to resolve spontaneously can result in overtreatment and unnecessary medical expenditure.

MULTIMEDIA

Section 9 of 10  

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

Media file 1:  Frontal radiograph of the pelvis. The ossification centers of the capital femoral epiphyses are symmetric and located in the joint spaces. Both heads project in the inner lower quadrants formed by the intersection of the Hilgenreiner (H) and Perkin (P) lines. Shenton lines (S) are continuous and demarcated by the dashed lines. The acetabular angles are symmetric and less than 28° bilaterally.
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Media file 2:  Frontal radiograph of the pelvis obtained in an infant before ossification of the capital femoral epiphyses begins. The legs are in the neutral position. The projected location of the unossified femoral heads must be estimated. The right hip is normal. The probable location of the left femoral head projects beyond the joint space and into the lower outer quadrant formed by the intersection of the Hilgenreiner and Perkin lines.
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Media type:  X-RAY

Media file 3:  Frontal radiograph of the pelvis in a 1-year-old child with a dislocated right hip. The degree of ossification of the femoral head on the dislocated side is decreased compared with that of the normally located left hip. The abnormally located hip articulates with a false neoacetabulum.
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Media type:  X-RAY

Media file 4:  Frontal radiograph of the pelvis obtained with the legs in the frog-leg position indicates that the plane of the femoral projection is toward the triradiate cartilage, suggesting that the hips are reducible.
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Media type:  X-RAY

Media file 5:  Schematic drawing of the coronal plane used to assess the hip at ultrasonography. The transducer is placed on the lateral aspect of the thigh.
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Media type:  Image

Media file 6:  Schematic drawing of the transverse plane of the left hip. The anteroposterior orientation depends on whether the right or left hip is being examined. The transducer is placed in the transverse orientation over the anterior upper thigh.
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Media type:  Image

Media file 7:  Calculation of the alpha and beta angles to assess acetabular maturity. A standard coronal image is used.
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Media type:  Image

Media file 8:  Real-time coronal sonogram of the hip shows calculation of the acetabular alpha angle. An angle of 60° or greater indicates acetabular maturity.
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Media type:  Image

Media file 9:  Real-time coronal sonogram of the hip with calculation of the d/D ratio. Coverage of 58% or greater is considered normal.
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Media type:  Image

Media file 10:  Real-time transverse sonogram of the right hip obtained without stress maneuvering reveals that the cartilaginous femoral head is well centered above the triradiate cartilage between the pubis and ischium. Echoes are present through the interface with the cartilage; this appearance has been likened to that of a lollipop, in which the femoral head is the "candy" and the echoes through the cartilage are the "stick." In a normally stable hip, this appearance should be maintained with stress maneuvering.
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Media type:  Image

Media file 11:  Real-time sonogram of the right hip obtained with stress maneuvering reveals that the femoral head is posteriorly displaced over the ischium.
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Media file 12:  Coronal real-time sonogram of the hip obtained with stress maneuvering reveals significant lateral motion, which is not out of the plane of the baseline. This was accompanied by posterior motion in the transverse plane.
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Media file 13:  Coronal real-time sonogram of the hip obtained with stress maneuvering reveals that the capital femoral epiphysis displaces out of the plane of the baseline. This dislocatable hip was reimaged after Ortolani maneuvering, and the dislocation was reducible.
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Media type:  Image

REFERENCES

Section 10 of 10

• Authors and Editors
• Introduction
• Differentials
• Radiograph
• CT SCAN
• MRI
• Ultrasound
• Intervention
• Multimedia
• References

1. Clinical practice guideline: early detection of developmental dysplasia of the hip. Committee on Quality Improvement, Subcommittee on Developmental Dysplasia of the Hip. American Academy of Pediatrics. Pediatrics. Apr 2000;105(4 Pt 1):896-905. [Medline].
2. Graf R. Guide to Sonography of the Infant Hip. New York, NY: Thieme Medical; 1987.
3. McMillan JA, DeAngelis CD, Warshaw JB, et al, eds. Oski's Pediatrics: Principles and Practice. 3^rd ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 1999.
4. Gerscovich EO. Infant hip in developmental dysplasia: facts to consider for a successful diagnostic ultrasound examination. Appl Radiol. 1999;Mar:18-25.
5. Nelson WE, Behrman RE, Kliegman RM, et al. Nelson Textbook of Pediatrics. 15^th ed. Philadelphia, Pa: WB Saunders; 1996.
6. Schwend RM, Schoenecker P, Richards BS, Flynn JM, Vitale M. Screening the newborn for developmental dysplasia of the hip: now what do we do?. J Pediatr Orthop. Sep 2007;27(6):607-10. [Medline].
7. Hennrikus WL. Developmental dysplasia of the hip: diagnosis and treatment in children younger than 6 months. Pediatr Ann. Dec 1999;28(12):740-6. [Medline].
8. American College of Radiology. ACR Standards, 1999-2000: American College of Radiology Standard for the Performance of the Ultrasound Examination for Detection of Developmental Dysplasia of the Hip. American College of Radiology. Available at http://www.acr.org/cgi-bin/fr?tmpl:standards00,pdf:pdf/hip_dysplasia.pdf. Accessed March 5, 2001.
9. Graf R. [The use of ultrasonography in developmental dysplasia of the hip.]. Acta Orthop Traumatol Turc. 2007;41 Suppl 1:6-13. [Medline].
10. Peled E, Eidelman M, Katzman A, Bialik V. Neonatal incidence of hip dysplasia: ten years of experience. Clin Orthop Relat Res. Apr 2008;466(4):771-5. [Medline].
11. Morin C, Harcke HT, MacEwen GD. The infant hip: real-time US assessment of acetabular development. Radiology. Dec 1985;157(3):673-7. [Medline].
12. Dezateux C, Rosendahl K. Developmental dysplasia of the hip. Lancet. May 5 2007;369(9572):1541-52. [Medline].
13. Kirks DR, Griscom NT. Practical Pediatric Imaging Diagnostic Radiology of Infants and Children. Philadelphia, Pa: Lippincott-Raven; 1998.
14. Ozonoff MB. Pediatric Orthopedic Radiology. 2^nd ed. Philadelphia, Pa: WB Saunders; 1992.
15. Wientroub S, Grill F. Ultrasonography in developmental dysplasia of the hip. J Bone Joint Surg Am. Jul 2000;82-A(7):1004-18. [Medline].
16. Tudor A, Sestan B, Rakovac I, Luke-Vrbanic TS, Prpic T, Rubinic D, et al. The rational strategies for detecting developmental dysplasia of the hip at the age of 4-6 months old infants: a prospective study. Coll Antropol. Jun 2007;31(2):475-81. [Medline].
17. Kotnis R, Spiteri V, Little C, Theologis T, Wainwright A, Benson MK. Hip arthrography in the assessment of children with developmental dysplasia of the hip and Perthes' disease. J Pediatr Orthop B. May 2008;17(3):114-119. [Medline].

Article Last Updated: May 20, 2008