breech presentation radiology

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INTRODUCTION

This topic will provide an overview of major issues related to breech presentation, including choosing the best route for delivery. Techniques for breech delivery, with a focus on the technique for vaginal breech delivery, are discussed separately. (See "Delivery of the singleton fetus in breech presentation" .)

TYPES OF BREECH PRESENTATION

● Frank breech – Both hips are flexed and both knees are extended so that the feet are adjacent to the head ( figure 1 ); accounts for 50 to 70 percent of breech fetuses at term.

● Complete breech – Both hips and both knees are flexed ( figure 2 ); accounts for 5 to 10 percent of breech fetuses at term.

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Introduction

Definitions, incidence, risk factors, and natural history, risk factors, natural history, screening and diagnosis, physical examination, radiography, ultrasonography, referral, adjunctive imaging, and treatment, adjunctive imaging, risks of treatment, medicolegal risk to the pediatrician, best practices and state of the art, acknowledgments, lead authors, section on orthopaedics executive committee, 2014–2015, evaluation and referral for developmental dysplasia of the hip in infants.

POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose.

FINANCIAL DISCLOSURE: The authors have indicated they do not have a financial relationship relevant to this article to disclose.

FUNDED: No external funding.

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Brian A. Shaw , Lee S. Segal , SECTION ON ORTHOPAEDICS , Norman Y. Otsuka , Richard M. Schwend , Theodore John Ganley , Martin Joseph Herman , Joshua E. Hyman , Brian A. Shaw , Brian G. Smith; Evaluation and Referral for Developmental Dysplasia of the Hip in Infants. Pediatrics December 2016; 138 (6): e20163107. 10.1542/peds.2016-3107

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Developmental dysplasia of the hip (DDH) encompasses a wide spectrum of clinical severity, from mild developmental abnormalities to frank dislocation. Clinical hip instability occurs in 1% to 2% of full-term infants, and up to 15% have hip instability or hip immaturity detectable by imaging studies. Hip dysplasia is the most common cause of hip arthritis in women younger than 40 years and accounts for 5% to 10% of all total hip replacements in the United States. Newborn and periodic screening have been practiced for decades, because DDH is clinically silent during the first year of life, can be treated more effectively if detected early, and can have severe consequences if left untreated. However, screening programs and techniques are not uniform, and there is little evidence-based literature to support current practice, leading to controversy. Recent literature shows that many mild forms of DDH resolve without treatment, and there is a lack of agreement on ultrasonographic diagnostic criteria for DDH as a disease versus developmental variations. The American Academy of Pediatrics has not published any policy statements on DDH since its 2000 clinical practice guideline and accompanying technical report. Developments since then include a controversial US Preventive Services Task Force “inconclusive” determination regarding usefulness of DDH screening, several prospective studies supporting observation over treatment of minor ultrasonographic hip variations, and a recent evidence-based clinical practice guideline from the American Academy of Orthopaedic Surgeons on the detection and management of DDH in infants 0 to 6 months of age. The purpose of this clinical report was to provide literature-based updated direction for the clinician in screening and referral for DDH, with the primary goal of preventing and/or detecting a dislocated hip by 6 to 12 months of age in an otherwise healthy child, understanding that no screening program has eliminated late development or presentation of a dislocated hip and that the diagnosis and treatment of milder forms of hip dysplasia remain controversial.

Early diagnosis and treatment of developmental dysplasia of the hip (DDH) is important to provide the best possible clinical outcome. DDH encompasses a spectrum of physical and imaging findings, from mild instability and developmental variations to frank dislocation. DDH is asymptomatic during infancy and early childhood, and, therefore, screening of otherwise healthy infants is performed to detect this uncommon condition. Traditional methods of screening have included the newborn and periodic physical examination and selected use of radiographic imaging. The American Academy of Pediatrics (AAP) promotes screening as a primary care function. However, screening techniques and definitions of clinically important clinical findings are controversial, and despite abundant literature on the topic, quality evidence-based literature is lacking.

The AAP last published a clinical practice guideline on DDH in 2000 titled “Early Detection of Developmental Dysplasia of the Hip.” 1 The purpose of this clinical report is to provide the pediatrician with updated information for DDH screening, surveillance, and referral based on recent literature, expert opinion, policies, and position statements of the AAP and the Pediatric Orthopaedic Society of North America (POSNA), and the 2014 clinical practice guideline of the American Academy of Orthopaedic Surgeons (AAOS). 1 , – 3  

A contributing factor to the DDH screening debate is lack of a uniform definition of DDH. DDH encompasses a spectrum of pathologic hip disorders in which hips are unstable, subluxated, or dislocated and/or have malformed acetabula. 1 However, imaging advancements, primarily ultrasonography, have created uncertainty regarding whether minor degrees of anatomic and physiologic variability are clinically significant or even abnormal, particularly in the first few months of life.

Normal development of the femoral head and acetabulum is codependent; the head must be stable in the hip socket for both to form spherically and concentrically. If the head is loose in the acetabulum, or if either component is deficient, the entire hip joint is at risk for developing incongruence and lack of sphericity. Most authorities refer to looseness as instability or subluxation and the actual physical deformity of the femoral head and/or acetabulum as dysplasia, but some consider hip instability itself to be dysplasia. Further, subluxation can be static (in which the femoral head is relatively uncovered without stress) or dynamic (the hip partly comes out of the socket with stress). The Ortolani maneuver, in which a subluxated or dislocated femoral head is reduced into the acetabulum with gentle hip abduction by the examiner, is the most important clinical test for detecting newborn dysplasia. In contrast, the Barlow maneuver, in which a reduced femoral head is gently adducted until it becomes subluxated or dislocated, is a test of laxity or instability and has less clinical significance than the Ortolani maneuver. In a practical sense, both maneuvers are performed seamlessly in the clinical assessment of an infant’s hip. Mild instability and morphologic differences at birth are considered by some to be pathologic and by others to be normal developmental variants.

In summary, there is lack of universal agreement on what measurable parameters at what age constitute developmental variation versus actual disease. Despite these differences in definition, there is universal expert agreement that a hip will fare poorly if it is unstable and morphologically abnormal by 2 to 3 years of age. It is the opinion of the AAP that DDH fulfills most screening criteria outlined by Wilson and Jungner 4 and that screening efforts are worthwhile to prevent a subluxated or dislocated hip by 6 to 12 months of age.

The Ortolani maneuver, in which a subluxated or dislocated femoral head is reduced into the acetabulum with gentle hip abduction by the examiner, is the most important clinical test for detecting newborn hip dysplasia.

The incidence of developmental dislocation of the hip is approximately 1 in 1000 live births. The incidence of the entire spectrum of DDH is undoubtedly higher but not truly known because of the lack of a universal definition. Rosendahl et al 5 noted a prevalence of dysplastic but stable hips of 1.3% in the general population. A study from the United Kingdom reported a 2% prevalence of DDH in girls born in the breech position. 6  

Important risk factors for DDH include breech position, female sex, incorrect lower-extremity swaddling, and positive family history. These risk factors are thought to be additive. Other suggested findings, such as being the first born or having torticollis, foot abnormalities, or oligohydramnios, have not been proven to increase the risk of “nonsyndromic” DDH. 3 , 7  

Breech presentation may be the most important single risk factor, with DDH reported in 2% to 27% of boys and girls presenting in the breech position. 6 , 8 , 9 Frank breech presentation in a girl (sacral presentation with hips flexed and knees extended) appears to have the highest risk. 1 Most evidence supports the breech position toward the end of pregnancy rather than breech delivery that contributes to DDH. There is no clear demarcation of timing of this risk; in other words, the point during pregnancy when the DDH risk is normalized by spontaneous or external version from breech to vertex position. Mode of delivery (cesarean) may decrease the risk of DDH with breech positioning. 10 , – 12 A recent study suggested that breech-associated DDH is a milder form than DDH that is not associated with breech presentation, with more rapid spontaneous normalization. 13  

Genetics may contribute more to the risk of DDH than previously considered “packaging effects.” If a monozygotic twin has DDH, the risk to the other twin is approximately 40%, and the risk to a dizygotic twin is 3%. 14 , 15 Recent research has confirmed that the familial relative risk of DDH is high, with first-degree relatives having 12 times the risk of DDH over controls. 16 , – 18 The left hip is more likely to be dysplastic than the right, which may be because of the more common in utero left occiput anterior position in nonbreech infants. 1 The AAOS clinical practice guideline considers breech presentation and family history to be the 2 most important risk factors in DDH screening. 3  

A lesser-known but important risk factor is the practice of swaddling, which has been gaining popularity in recent years for its noted benefits of enhancing better sleep patterns and duration and minimizing hypothermia. However, these benefits are countered by the apparent increased rates of DDH observed in several ethnic groups, such as Navajo Indian and Japanese populations, that have practiced traditional swaddling techniques. Traditional swaddling maintains the hips in an extended and adducted position, which increases the risk of DDH. However, the concept of “safe swaddling,” which allows for hip flexion and abduction and knee flexion, has been shown to lessen the risk of DDH ( http://hipdysplasia.org/developmental-dysplasia-of-the-hip/hip-healthy-swaddling/ ). Parents can be taught the principles of safe infant sleep, including supine position in the infant’s own crib and not the parent’s bed, with no pillows, bumpers, or loose blankets. 19 , – 24 The POSNA, International Hip Dysplasia Institute, AAOS, United States Bone and Joint Initiative, and Shriners Hospitals for Children have published a joint statement regarding the importance of safe swaddling in preventing DDH. 25  

In general, risk factors are poor predictors of DDH. Female sex, alone without other known risk factors, accounts for 75% of DDH. This emphasizes the importance of a careful physical examination of all infants in detecting DDH. 6 A recent survey showed poor consensus on risk factors for DDH from a group of experts. 26  

In general, risk factors are poor predictors of DDH. Female sex, alone without other known risk factors, accounts for 75% of DDH.

Clinical and imaging studies show that the natural history of mild dysplasia and instability noted in the first few weeks of life is typically benign. Barlow-positive (subluxatable and dislocatable) hips resolve spontaneously, and Barlow himself noted that the mild dysplasia in all 250 newborn infants with positive test results in his original study resolved spontaneously. 27 , – 32  

Conversely, the natural history of a child with hip dysplasia at the more severe end of the disease spectrum (subluxation or dislocation) by walking age is less satisfactory than children treated successfully at a younger age. Without treatment, these children will likely develop a limp, limb length discrepancy, and limited hip abduction. This may result in premature degenerative arthritis in the hip, knee, and low back. The burden of disability is high, because most affected people become symptomatic in their teens and early adult years, and most require complex hip salvage procedures and/or replacement at an early age.

The 2000 AAP clinical practice guideline recommended that all newborn infants be screened for DDH by physical examination, with follow-up at scheduled well-infant periodic examinations. The POSNA, the Canadian Task Force on DDH, and the AAOS have also advocated newborn and periodic screening. A 2006 report by the US Preventive Services Task Force (USPSTF) resulted in controversy regarding DDH screening. By using a data-driven model and a strong emphasis on the concept on predictors of poor health, the USPSTF report gave an “I” recommendation, meaning that the evidence was insufficient to recommend routine screening for DDH in infants as a means to prevent adverse outcomes. 1 , – 3 , 33 , – 35 However, on the basis of the body of evidence when evaluated from the perspective of a clinical practice model, the AAP advocates for DDH screening.

In its report, the USPSTF noted that avascular necrosis (AVN) is the most common (up to 60%) and severe potential harm of both surgical and nonsurgical interventions. 33 Williams et al 36 reported the risk of AVN to be less than 1% with screening, early detection, and the use of the Pavlik harness. In a long-term follow-up study of a randomized controlled trial from Norway, the authors reported no cases of AVN and no increased risk of harm with increased treatment. 37 The USPSTF also raised concerns about the psychological consequences or stresses with early diagnosis and intervention. Gardner et al 38 found that the use of hip ultrasonography allowed for reduction of treatment rates without adverse clinical or psychological outcomes. Thus, the concerns of AVN and psychological distress or potential predictors of poor health have not been supported in literature not referenced in the USPSTF report.

In 2 well-designed, randomized controlled trial studies from Norway, the prevalence of late DDH presentation was reduced from 2.6 to 3.0 per 1000 to 0.7 to 1.3 per 1000 by using either selective or universal hip ultrasonographic screening. Neither study reached statistical significance because of the inadequate sample size on the basis of prestudy rates of late-presentation DDH. Despite this, both centers have introduced selective hip ultrasonography as part of their routine newborn screening. 39 , 40 Clarke et al 32 also demonstrated a decrease in late DDH presentation from 1.28 per 1000 to 0.74 per 1000 by using selective hip ultrasonography in a prospective cohort of patients over a 20-year period.

The term “surveillance” may be useful nomenclature to consider in place of screening, because, by definition, it means the close monitoring of someone or something to prevent an adverse outcome. The term surveillance reinforces the concept of periodic physical examinations as part of well-child care visits until 6 to 9 months of age and the use of selective hip ultrasonography as an adjunct imaging tool or an anteroposterior radiograph of the pelvis after 4 months of age for infants with identified risk factors. 3 , 5 , 32 , 41  

Wilson and Jungner 4 outlined 10 principles or criteria to consider when determining the utility of screening for a disease. The AAP believes DDH fulfills most of these screening criteria ( Table 1 ), except for an understanding of the natural history of hip dysplasia and an agreed-on policy of whom to treat. The 2006 USPSTF report and the AAOS clinical practice guideline provide a platform to drive future research in these 2 areas. Screening for DDH is important, because the condition is initially occult, easier to treat when identified early, and more likely to cause long-term disability if detected late. A reasonable goal for screening is to prevent the late presentation of DDH after 6 months of age.

World Health Organization Criteria for Screening for Health Problems

The physical examination is by far the most important component of a DDH screening program, with imaging by radiography and/or ultrasonography playing a secondary role. It remains the “cornerstone” of screening and/or surveillance for DDH, and the available evidence supports that primary care physicians serially examine infants previously screened with normal hip examinations on subsequent visits up to 6 to 9 months of age. 3 , 41 , – 44 Once a child is walking, a dislocated hip may manifest as an abnormal gait.

The 2000 AAP clinical practice guideline gave a detailed description of the examination, including observing for limb length discrepancy, asymmetric thigh or gluteal folds, and limited or asymmetric abduction, as well as performing Barlow and Ortolani tests. 1 It is essential to perform these manual tests gently. By ∼3 months of age, a dislocated hip becomes fixed, limiting the usefulness and sensitivity of the Barlow and Ortolani tests. By this age, restricted, asymmetric hip abduction of the involved hip becomes the most important finding (see video available at http://www.aap.org/sections/ortho ). Diagnosing bilateral DDH in the older infant can be difficult because of symmetry of limited abduction.

Although ingrained in the literature, the significance and safety of the Barlow test is questioned. Barlow stated in his original description that the test is for laxity of the hip joint rather than for an existing dislocation. The Barlow test has no proven predictive value for future hip dislocation. If performed frequently or forcefully, it is possible that the maneuver itself could create instability. 45 , 46 The AAP recommends, if the Barlow test is performed, that it be done by gently adducting the hip while palpating for the head falling out the back of the acetabulum and that no posterior-directed force be applied. One can think of the Barlow and Ortolani tests as a continuous smooth gentle maneuver starting with the hip flexed and adducted, with gentle anterior pressure on the trochanter while the hip is abducted to feel whether the hip is locating into the socket, followed by gently adducting the hip and relieving the anterior pressure on the trochanter while sensing whether the hip slips out the back. The examiner should not attempt to forcefully dislocate the femoral head (see video available at http://www.aap.org/sections/ortho ).

“Hip clicks” without the sensation of instability are clinically insignificant. 47 Whereas the Ortolani sign represents the palpable sensation of the femoral head moving into the acetabulum over the hypertrophied rim of the acetabular cartilage (termed neolimbus), isolated high-pitched clicks represent the movement of myofascial tissues over the trochanter, knee, or other bony prominences and are not a sign of hip dysplasia or instability.

Plain radiography becomes most useful by 4 to 6 months of age, when the femoral head secondary center of ossification forms. 48 Limited evidence supports obtaining a properly positioned anteroposterior radiograph of the pelvis. 3 If the pelvis is rotated or if a gonadal shield obscures the hip joint, then the radiograph should be repeated. Hip asymmetry, subluxation, and dislocation can be detected on radiographs when dysplasia is present. There is debate about whether early minor radiographic variability (such as increased acetabular index) constitutes actual disease. 31 Radiography is traditionally indicated for diagnosis of the infant with risk factors or an abnormal examination after 4 months of age. 1 , 2 , 8 , 49  

Ultrasonography can provide detailed static and dynamic imaging of the hip before femoral head ossification. The American Institute of Ultrasound in Medicine and the American College of Radiology published a joint guideline for the standardized performance of the infantile hip ultrasonographic examination. 50 Static ultrasonography shows coverage of the femoral head by the cartilaginous acetabulum (α angle) at rest, and dynamic ultrasonography demonstrates a real-time image of the Barlow and Ortolani tests.

Ultrasonographic imaging can be universal for all infants or selective for those at risk for having DDH. Universal newborn ultrasonographic screening is not recommended in North America because of the expense, inconvenience, inconsistency, subjectivity, and high false-positive rates, given an overall population disease prevalence of 1% to 2%. 3 Rather, selective ultrasonographic screening is recommended either to clarify suspicious findings on physical examination after 3 to 4 weeks of age or to detect clinically silent DDH in the high-risk infant from 6 weeks to 4 to 6 months of age. 1 , 2 , 35 , 50 Two prospective randomized clinical trials from Norway support selective ultrasonographic imaging when used in conjunction with high-quality clinical screening. 39 , 40  

Roposch and colleagues 51 , 52 contend that experts cannot reach a consensus on what is normal, abnormal, developmental variation, or simply uncertain regarding much ultrasonographic imaging, thereby confounding referral and treatment recommendations. Several studies have demonstrated that mild ultrasonographic abnormalities usually resolve spontaneously, fueling the controversy over what imaging findings constitute actual disease requiring treatment. 5 , 30 , 51 , 53 , – 56  

The concept of surveillance for DDH emphasizes the importance of repeated physical examinations and the adjunct use of selective hip ultrasonography after 6 weeks of age or an anteroposterior radiograph of the pelvis after 4 months of age for infants with questionable or abnormal findings on physical examination or with identified risk factors. Ultrasonography is not necessary for a frankly dislocated hip (Ortolani positive) but may be desired by the treating physician. Physiologic joint capsular laxity and immature acetabular development before 6 weeks of age may limit the accuracy of hip ultrasonography interpretations. 39 , 40 There is no consensus on exact timing of and indications for ultrasonography among expert groups. 26 , 57 However, ultrasonographic imaging does have a management role in infants younger than 6 weeks undergoing abduction brace treatment of unstable hips identified on physical examination. 3  

Early detection and referral of infants with DDH allows appropriate intervention with bracing or casting, which may prevent the need for reconstructive surgery. Primary indications for referral include an unstable (positive Ortolani test result) or dislocated hip on clinical examination. Because most infants with a positive Barlow test result at either the newborn or 2-week examination stabilize on their own, these infants should have sequential follow-up examinations as part of the concept of surveillance. This recommendation differs from the 2000 AAP clinical practice guideline. 1 Any child with limited hip abduction or asymmetric hip abduction after the neonatal period (4 weeks) should be referred. Relative indications for referral include infants with risk factors for DDH, a questionable examination, and pediatrician or parental concern. 1  

Recommendations for the evaluation and management of infants with risk factors for DDH but with normal findings on physical examination continue to evolve. The 2000 AAP clinical practice guideline recommended hip ultrasonography at 6 weeks of age or radiography of the pelvis and hips at 4 months of age in girls with a positive family history of DDH or breech presentation. The AAP clinical practice guideline also stated that hip ultrasonographic examinations remain an option for all infants born breech. 1 The recent AAOS report found that moderate evidence supports an imaging study before 6 months of age in infants with breech presentation, family history, and/or history of clinical instability. 3 , 58 , – 60  

Consider imaging before 6 months of age for male or female infants with normal findings on physical examination and the following risk factors:

Breech presentation in third trimester (regardless of cesarean or vaginal delivery)

Positive family history

History of previous clinical instability

Parental concern

History of improper swaddling

Suspicious or inconclusive physical examination

Refinement in the term “breech presentation” as a risk factor for DDH is needed to determine whether selective hip ultrasonography at 6 weeks or radiography before 6 months of age is needed for an infant with a normal clinical hip examination. More specific variables, such as mode of delivery, type of breech position, or breech position at any time during the pregnancy or in the third trimester, have received little attention to date. The AAOS clinical practice guideline reported 6 studies addressing breech presentation, but all were considered low-strength evidence. 3 Thus, the literature is not adequate enough to allow specific guidance. The risk is thought to be greater for frank breech (hips flexed, knees extended) in the last trimester. 1  

Lacking expert consensus of risk factors for DDH, 26 the questions of whether to obtain additional imaging studies with a normal clinical hip examination is ultimately best left to one’s professional judgment. One must consider, however, that the overall probability of a clinically stable hip to later dislocate is very low.

Because of the variability in performance and interpretation of the hip ultrasonographic examination and varying thresholds for treatment, the requesting physician might consider developing a regional protocol in conjunction with a consulting pediatric orthopedist and pediatric radiologist. Specific criteria for imaging and referral based on local resources can promote consistency in evaluation and treatment of suspected DDH. Realistically, many families may not have ready access to quality infant hip ultrasonography, and this may determine the choice of obtaining a pelvic radiograph instead of an ultrasound. 61  

Recommendations for treatment are based on the clinical hip examination and the presence or absence of imaging abnormalities. Infants with a stable clinical hip examination but with abnormalities noted on ultrasonography can be observed without a brace. 3 , 56  

The initiation of abduction brace treatment, either immediate or delayed, for clinically unstable hips is supported by several studies. 3 , 62 , – 64 In a randomized clinical trial, Gardiner and Dunn 62 found no difference in hip ultrasonography findings or clinical outcome for infants with dislocatable hips treated with either immediate or delayed abduction bracing at 6- and 12-month follow-up. The infants in the delayed group (2 weeks) were treated with abduction bracing if hip instability persisted or the hip ultrasonographic abnormalities did not improve. 62  

Treatment of clinically unstable hips usually consists of bracing when discovered in early infancy and closed reduction with adductor tenotomy and spica cast immobilization when noted later. After 18 months of age, open surgery is generally recommended.

As previously noted, the 2006 USPSTF report noted a high rate of AVN, up to 60% with both surgical and nonsurgical intervention. 33 Other studies have reported much lower rates of AVN. 36 , 37 One prospective study reported a zero prevalence of AVN by 6 years of age in mildly dysplastic hips treated with bracing. 30  

However, abduction brace treatment is not innocuous. The potential risks include AVN, temporary femoral nerve palsy, and obturator (inferior) hip dislocation. 65 , – 67 One study demonstrated a 7% to 14% risk of complications after treatment in a Pavlik harness. The risk was greater in hips that did not reduce in the brace. 33 Precautions such as avoiding forced abduction in the harness, stopping treatment after 3 weeks if the hip does not reduce, and proper strap placement with weekly monitoring is important to minimize the risks associated with brace treatment. 68 , 69 Double diapering is a probably harmless but ineffective treatment of true DDH.

What remains controversial is whether the selective use of ultrasonography reduces or increases treatment. A randomized controlled study from the United Kingdom showed that approximately half of all positive physical examination findings were falsely positive (ie, normal ultrasonography results) and that the use of ultrasonography in clinically suspect hips actually reduced DDH treatment. 60 However, in the United States and Canada, 21 the reverse appears to be true. In the current medicolegal climate that encourages a defensive approach, liberal use of ultrasonography in the United States and Canada has clearly fostered overdiagnosis and overtreatment of DDH, despite best-available literature supporting observation of mild dysplasia. 33 , – 35 , 70  

Undetected or late-developing DDH is a liability concern for the pediatrician, generating anxiety and a desire for guidance in best screening methodology. 71 Unfortunately, this fear may also provoke overdiagnosis and overtreatment. “Late-presenting” DDH is a more accurate term than “missed” to use when DDH is first diagnosed in a walking-aged child who had appropriate clinical examinations during infancy. 72 , 73  

Although there is no universally recognized DDH screening standard, the AAP endorses the concept of surveillance or periodic physical examinations until walking age, with selective use of either hip ultrasonography or radiography, depending on age. The AAP cautions against overreliance on ultrasonography as a diagnostic test and encourages its use as an adjunctive secondary screen and an aid to treatment of established DDH. Notably, no screening program has been shown to completely eliminate the risk of a late-presenting dislocated hip. 69  

The electronic health record can be used to provide a template, reminder, and documentation tool for the periodic examination. It also can be useful in the transition and comanagement of children with suspected DDH by providing effective information transfer between consultants and primary care physicians and ensuring follow-up. Accurate documented communication between providers is important to provide continuity of care for this condition, and it is also important to explain to the parent(s) and document those instances when observation is used as a planned strategy so it is less likely to be misinterpreted as negligence.

The AAP, POSNA, AAOS, and Canadian DDH Task Force recommend newborn and periodic surveillance physical examinations for DDH to include detection of limb length discrepancy, examination for asymmetric thigh or buttock (gluteal) creases, performing the Ortolani test for stability (performed gently and which is usually negative after 3 months of age), and observing for limited abduction (generally positive after 3 months of age). Use of electronic health records can be considered to prompt and record the results of periodic hip examinations. The AAP recommends against universal ultrasonographic screening.

Selective hip ultrasonography can be considered between the ages of 6 weeks and 6 months for “high-risk” infants without positive physical findings. High risk is a relative and controversial term, but considerations include male or female breech presentation, a positive family history, parental concern, suspicious but inconclusive periodic examination, history of a previous positive instability physical examination, and history of tight lower-extremity swaddling. Because most DDH occurs in children without risk factors, physical examination remains the primary screening tool.

It is important that infantile hip ultrasonography be performed and interpreted per American Institute of Ultrasound in Medicine and the American College of Radiology guidelines by experienced, trained examiners. Developing local criteria for screening imaging and referral based on best resources may promote more uniform and cost-effective treatment. Regional variability of ultrasonographic imaging quality can lead to under- or overtreatment.

Most minor hip anomalies observed on ultrasonography at 6 weeks to 4 months of age will resolve spontaneously. These include minor variations in α and β angles and subluxation (“uncoverage”) with stress maneuvers. Current levels of evidence do not support recommendations for treatment versus observation in any specific case of minor ultrasonographic variation. Care is, therefore, individualized through a process of shared decision-making in this setting of inadequate information.

Radiography (anteroposterior and frog pelvis views) can be considered after 4 months of age for the high-risk infant without physical findings or any child with positive clinical findings. Age 4 to 6 months is a watershed during which either imaging modality may be used; radiography is more readily available, has a lower rate of false-positive results, and is less expensive than ultrasonography but involves a very low dose of radiation.

A referral to an orthopedist for DDH does not require ultrasonography or radiography. The primary indication for referral includes an unstable (positive Ortolani test result) or dislocated hip on clinical examination. Any child with limited hip abduction or asymmetric hip abduction after the neonatal period (4 weeks of age) should be referred for evaluation. Relative indications for referral include infants with risk factors for DDH, a questionable examination, and pediatrician or parental concern.

Evidence strongly supports screening for and treatment of hip dislocation (positive Ortolani test result) and initially observing milder early forms of dysplasia and instability (positive Barlow test result). Depending on local custom, either the pediatrician or the orthopedist can observe mild forms by periodic examination and possible follow-up imaging, but actual treatment should be performed by an orthopedist.

A reasonable goal for the primary care physician should be to diagnose hip subluxation or dislocation by 6 months of age by using the periodic physical examination. Selective ultrasonography or radiography may be used in consultation with a pediatric radiologist and/or orthopedist. No screening program has been shown to completely eliminate the risk of a late presentation of DDH. There is no high-level evidence that milder forms of dysplasia can be prevented by screening and early treatment.

Tight swaddling of the lower extremities with the hips adducted and extended should be avoided. The concept of “safe” swaddling, which does not restrict hip motion, minimizes the risk of DDH.

Treatment of neonatal DDH is not an emergency, and in-hospital initiation of bracing is not required. Orthopaedic consultation can be safely obtained within several weeks of discharge for an infant with a positive Ortolani test result. Infants with a positive Barlow test results should be reexamined and referred to an orthopedist if they continue to show clinical instability.

American Academy of Orthopaedic Surgeons

American Academy of Pediatrics

avascular necrosis

developmental dysplasia of the hip

Pediatric Orthopaedic Society of North America

US Preventive Services Task Force

This document is copyrighted and is property of the American Academy of Pediatrics and its Board of Directors. All authors have filed conflict of interest statements with the American Academy of Pediatrics. Any conflicts have been resolved through a process approved by the Board of Directors. The American Academy of Pediatrics has neither solicited nor accepted any commercial involvement in the development of the content of this publication.

Clinical reports from the American Academy of Pediatrics benefit from expertise and resources of liaisons and internal (AAP) and external reviewers. However, clinical reports from the American Academy of Pediatrics may not reflect the views of the liaisons or the organizations or government agencies that they represent.

The guidance in this report does not indicate an exclusive course of treatment or serve as a standard of medical care. Variations, taking into account individual circumstances, may be appropriate.

All clinical reports from the American Academy of Pediatrics automatically expire 5 years after publication unless reaffirmed, revised, or retired at or before that time.

The authors thank Charles Price, MD, FAAP, Ellen Raney, MD, FAAP, Joshua Abzug, MD, FAAP, and William Hennrikus, MD, FAAP, for their valuable contributions to this report.

Brian A. Shaw, MD, FAAOS, FAAP

Lee S. Segal, MD, FAAP

Norman Y. Otsuka, MD, FAAP, Chairperson

Richard M. Schwend, MD, FAAP, Immediate Past Chairperson

Theodore John Ganley, MD, FAAP

Martin Joseph Herman, MD, FAAP

Joshua E. Hyman, MD, FAAP

Brian G. Smith, MD, FAAP

Niccole Alexander, MPP

Competing Interests

Re: breech presentation in preterm infants.

Thanks for the excellent review highlighting the controversies around screening, imaging and management of DDH. I have a question to the authors re: preterm infants. If an infant is born premature in third trimester with breech presentation and a normal hip examination at birth, would the authors recommend considering a hip ultrasound after 6 weeks post-menstrual age or 6 weeks chronologic age?

RE: Late diagnosis of developmental dysplasia of the hip can be eradicated

The survey published by Shaw and al in the December issue of Pediatrics concluded that no screening program has eliminated late development or presentation of a dislocated hip (1).

In the literature, there is controversy over widespread ultrasound screening since its ability to prevent late DDH diagnosis has not been proven (2,3). Techniques mainly relied on acetabular morphology classifications with no clear cut-off for early DDH diagnosis. Results are not enough reproducible for a large screening program involving non-expert radiologists (4). Moreover the effect of hip instability on acetabular shape may not be seen at one month old. These three reasons explain the failure of almost all screening programs based on these techniques.

Our experience is based on dynamic assessment of the femoral head position based on pubo-femoral distance (PFD) measurements. The normal PFD is lower than or equal to 6mm, with no more than 1.5mm between the hips (5). This simple, reliable, and reproducible method was easily taught to general radiologists involved in the screening program. With the support of perinatal network pediatricians, ultrasound screening was offered to all girls and to boys presenting with risk factors or abnormalities on clinical examination at one month old. All reports indicate a prevalence of 90% for girls, 70% with no risk factors. All infants with positive screenings were immediately referred to multidisciplinary teams involving an expert radiologist and orthopedic pediatrician. At one month old, reducible hip instability was always successfully treated by abduction splint. In 2013, we published that late diagnosis of DDH was eradicated from our region (annual births: 14,000) over a 3-year period from 2009 to 2011 (5). This period has now reached 8 years in a region of more than 1 million inhabitants in which our institution is the only referral center. Brittany (France), country of Dr Le Damany who described this disease, has a high prevalence of DDH (6/1000).

These long-term results are unique and confirm that ultrasound measurement of PFD provides a clear cut-off for DDH detection. Based on this simple technique, widespread screening, at least in girls, could eradicate late DDH diagnosis.

References:

1. Shaw BA, Segal LS. Evaluation and Referral for Developmental Dysplasia of the Hip in Infants. Pediatrics. 2016;138(6):e20163107 2. von Kries R, Ihme N, Altenhofen L, Niethard FU, Krauspe R, Rückinger S. General ultrasound screening reduces the rate of first operative procedures for developmental dysplasia of the hip: a case-control study. J Pediatr. 2012;160(2):271–5. 3. Laborie LB, Markestad TJ, Davidsen H, Brurås KR, Aukland SM, Bjørlykke JA, et al. Selective ultrasound screening for developmental hip dysplasia: effect on management and late detected cases. A prospective survey during 1991-2006. Pediatr Radiol. 2014;44(4):410–24.

4. Roposch A, Moreau NM, Uleryk E, Doria AS (2006) Developmental dysplasia of the hip: quality of reporting of diagnostic accuracy for US. Radiology, 241(3):854-860.. 5. Tréguier C, Chapuis M, Branger B, Bruneau B, Grellier A, Chouklati K, et al. Pubo-femoral distance: an easy sonographic screening test to avoid late diagnosis of developmental dysplasia of the hip. Eur Radiol. 2013 Mar;23(3):836–44.

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Fetal Presentation, Position, and Lie (Including Breech Presentation)

, MD, Children's Hospital of Philadelphia

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Abnormal fetal lie or presentation may occur due to fetal size, fetal anomalies, uterine structural abnormalities, multiple gestation, or other factors. Diagnosis is by examination or ultrasonography. Management is with physical maneuvers to reposition the fetus, operative vaginal delivery Operative Vaginal Delivery Operative vaginal delivery involves application of forceps or a vacuum extractor to the fetal head to assist during the second stage of labor and facilitate delivery. Indications for forceps... read more , or cesarean delivery Cesarean Delivery Cesarean delivery is surgical delivery by incision into the uterus. The rate of cesarean delivery was 32% in the United States in 2021 (see March of Dimes: Delivery Method). The rate has fluctuated... read more .

Terms that describe the fetus in relation to the uterus, cervix, and maternal pelvis are

Fetal presentation: Fetal part that overlies the maternal pelvic inlet; vertex (cephalic), face, brow, breech, shoulder, funic (umbilical cord), or compound (more than one part, eg, shoulder and hand)

Fetal position: Relation of the presenting part to an anatomic axis; for transverse presentation, occiput anterior, occiput posterior, occiput transverse

Fetal lie: Relation of the fetus to the long axis of the uterus; longitudinal, oblique, or transverse

Normal fetal lie is longitudinal, normal presentation is vertex, and occiput anterior is the most common position.

Abnormal fetal lie, presentation, or position may occur with

Fetopelvic disproportion (fetus too large for the pelvic inlet)

Fetal congenital anomalies

Uterine structural abnormalities (eg, fibroids, synechiae)

Multiple gestation

Several common types of abnormal lie or presentation are discussed here.

Transverse lie

Fetal position is transverse, with the fetal long axis oblique or perpendicular rather than parallel to the maternal long axis. Transverse lie is often accompanied by shoulder presentation, which requires cesarean delivery.

Breech presentation

There are several types of breech presentation.

Frank breech: The fetal hips are flexed, and the knees extended (pike position).

Complete breech: The fetus seems to be sitting with hips and knees flexed.

Single or double footling presentation: One or both legs are completely extended and present before the buttocks.

Types of breech presentations

Breech presentation makes delivery difficult ,primarily because the presenting part is a poor dilating wedge. Having a poor dilating wedge can lead to incomplete cervical dilation, because the presenting part is narrower than the head that follows. The head, which is the part with the largest diameter, can then be trapped during delivery.

Additionally, the trapped fetal head can compress the umbilical cord if the fetal umbilicus is visible at the introitus, particularly in primiparas whose pelvic tissues have not been dilated by previous deliveries. Umbilical cord compression may cause fetal hypoxemia.

Predisposing factors for breech presentation include

Preterm labor Preterm Labor Labor (regular uterine contractions resulting in cervical change) that begins before 37 weeks gestation is considered preterm. Risk factors include prelabor rupture of membranes, uterine abnormalities... read more

Multiple gestation Multifetal Pregnancy Multifetal pregnancy is presence of > 1 fetus in the uterus. Multifetal (multiple) pregnancy occurs in up to 1 of 30 deliveries. Risk factors for multiple pregnancy include Ovarian stimulation... read more

Uterine abnormalities

Fetal anomalies

If delivery is vaginal, breech presentation may increase risk of

Umbilical cord prolapse

Perinatal death

It is best to detect abnormal fetal lie or presentation before delivery. During routine prenatal care, clinicians assess fetal lie and presentation with physical examination in the late third trimester. Ultrasonography can also be done. If breech presentation is detected, external cephalic version can sometimes move the fetus to vertex presentation before labor, usually at 37 or 38 weeks. This technique involves gently pressing on the maternal abdomen to reposition the fetus. A dose of a short-acting tocolytic ( terbutaline 0.25 mg subcutaneously) may help. The success rate is about 50 to 75%. For persistent abnormal lie or presentation, cesarean delivery is usually done at 39 weeks or when the woman presents in labor.

Face or brow presentation

In face presentation, the head is hyperextended, and position is designated by the position of the chin (mentum). When the chin is posterior, the head is less likely to rotate and less likely to deliver vaginally, necessitating cesarean delivery.

Brow presentation usually converts spontaneously to vertex or face presentation.

Occiput posterior position

The most common abnormal position is occiput posterior.

The fetal neck is usually somewhat deflexed; thus, a larger diameter of the head must pass through the pelvis.

Progress may arrest in the second phase of labor. Operative vaginal delivery Operative Vaginal Delivery Operative vaginal delivery involves application of forceps or a vacuum extractor to the fetal head to assist during the second stage of labor and facilitate delivery. Indications for forceps... read more or cesarean delivery Cesarean Delivery Cesarean delivery is surgical delivery by incision into the uterus. The rate of cesarean delivery was 32% in the United States in 2021 (see March of Dimes: Delivery Method). The rate has fluctuated... read more is often required.

Position and Presentation of the Fetus

If a fetus is in the occiput posterior position, operative vaginal delivery or cesarean delivery is often required.

In breech presentation, the presenting part is a poor dilating wedge, which can cause the head to be trapped during delivery, often compressing the umbilical cord.

For breech presentation, usually do cesarean delivery at 39 weeks or during labor, but external cephalic version is sometimes successful before labor, usually at 37 or 38 weeks.

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Chapter 25:  Breech Presentation

Jessica Dy; Darine El-Chaar

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General considerations.

• CLASSIFICATION
• RIGHT SACRUM ANTERIOR
• MECHANISMS OF LABOR: BREECH PRESENTATIONS
• PROGNOSIS: BREECH PRESENTATIONS
• INVESTIGATION OF BREECH PRESENTATION AT TERM
• MANAGEMENT OF BREECH PRESENTATION DURING LATE PREGNANCY
• MANAGEMENT OF DELIVERY OF BREECH PRESENTATION
• ARREST IN BREECH PRESENTATION
• BREECH EXTRACTION
• HYPEREXTENSION OF THE FETAL HEAD
• SELECTED READING
• Full Chapter
• Supplementary Content

Breech presentation is a longitudinal lie with a variation in polarity. The fetal pelvis is the leading pole. The denominator is the sacrum. A right sacrum anterior (RSA) is a breech presentation where the fetal sacrum is in the right anterior quadrant of the mother's pelvis and the bitrochanteric diameter of the fetus is in the right oblique diameter of the pelvis ( Fig. 25-1 ).

FIGURE 25-1.

Positions of breech presentation. LSA, left sacrum anterior; LSP, left sacrum posterior; LST, left sacrum transverse; RSA, right sacrum anterior; RSP, right sacrum posterior; RST, right sacrum transverse.

Breech presentation at delivery occurs in 3 to 4 percent of pregnancies. However, before 28 weeks of gestation, the incidence is about 25 percent. As term gestation approaches, the incidence decreases. In most cases, the fetus converts to the cephalic presentation by 34 weeks of gestation.

As term approaches, the uterine cavity, in most cases, accommodates the fetus best in a longitudinal lie with a cephalic presentation. In many cases of breech presentation, no reason for the malpresentation can be found and, by exclusion, the cause is ascribed to chance. Some women deliver all their children as breeches, suggesting that the pelvis is so shaped that the breech fits better than the head.

Breech presentation is more common at the end of the second trimester than near term; hence, fetal prematurity is associated frequently with this presentation.

Maternal Factors

Factors that influence the occurrence of breech presentation include (1) the uterine relaxation associated with high parity; (2) polyhydramnios, in which the excessive amount of amniotic fluid makes it easier for the fetus to change position; (3) oligohydramnios, in which, because of the small amount of fluid, the fetus is trapped in the position assumed in the second trimester; (4) uterine anomalies; (5) neoplasms, such as leiomyomata of the myometrium; (6) while contracted pelvis is an uncommon cause of breech presentation, anything that interferes with the entry of the fetal head into the pelvis may play a part in the etiology of breech presentation.

Placental Factors

Placental site: There is some evidence that implantation of the placenta in either cornual-fundal region tends to promote breech presentation. There is a positive association of breech with placenta previa.

Fetal Factors

Fetal factors that influence the occurrence of breech presentation include multiple pregnancy, hydrocephaly, anencephaly, chromosomal anomalies, and intrauterine fetal death.

Notes and Comments

The patient commonly feels fetal movements in the lower abdomen and may complain of painful kicking against the rectum, vagina, and bladder

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At the time the article was created Frank Gaillard had no recorded disclosures.

At the time the article was last revised Yuranga Weerakkody had no financial relationships to ineligible companies to disclose.

• Developmental dysplasia of the hip (DDH)
• Developmental dysplasia of hip (DDH)
• Developmental hip dysplasia
• Congenital dislocation of the hip (CDH)
• Hip dysplasia
• Developmental dysplasia of the hips
• Developmental dysplasia of hips
• Congenital dislocation of the hips
• Congenital dislocation of hip

Developmental dysplasia of the hip (DDH) , or in older texts congenital dislocation of the hip (CDH) , denotes aberrant development of the hip joint and results from an abnormal relationship of the femoral head to the acetabulum .

Unlike congenital dislocation of the hip, developmental dysplasia of the hip is not confined to congenital malformations and includes perturbations in development 12 . There is a clear female predominance, and it usually occurs from ligamentous laxity and abnormal position in utero. Therefore, it is more common with oligohydramniotic pregnancies. This article describes the commonly used radiographic measurements and lines involved in developmental dysplasia of the hip.

On this page:

Epidemiology, clinical presentation, radiographic features, treatment and prognosis.

• Cases and figures

The reported incidence of developmental dysplasia of the hip varies between 1.5-20 per 1000 births 1 , with the majority (60-80%) of abnormal hips resolving spontaneously within 2-8 weeks 1 (so-called immature hip).

Risk factors

Risk factors include 1,4 :

female gender (M:F ~1:8)

firstborn baby

family history

breech presentation

oligohydramnios

metatarsus adductus

spina bifida   9

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Developmental dysplasia of the hip is usually suspected in the early neonatal period due to the widespread adoption of clinical examination (including the Ortolani test, Barlow maneuvers, and Galeazzi sign). The diagnosis is then usually confirmed with ultrasound, although the role of ultrasound in screening is controversial 1,3 .

In general, the dysplastic hip has a ridge ( neolimbus ) in the superolateral region of the acetabulum composed of hypertrophied fibrocartilage as a result of the abnormal joint congruity 13 . In addition, there is very cellular hyaline cartilage allowing the femoral head to glide out of the acetabulum generating the palpable clunk known as the Ortolani sign 12,13 .

For imaging assessment of developmental dysplasia of the hip, ultrasound is the modality of choice prior to the ossification of the proximal femoral epiphysis. Once there is a significant ossification then an x-ray examination is required.

For some reason, the left hip is said to be more frequently affected 4 . One-third of cases are affected bilaterally 5 .

Ultrasound is the test of choice in the infant (<6 months) as the proximal femoral epiphysis has not yet significantly ossified. Additionally, it has the advantage of being a real-time dynamic examination allowing the stability of the hip to be assessed with stress views. 

Some values are used to "objectively" assess morphology. See  Graf method for ultrasound classification of developmental dysplasia of the hip .

Acetabular rounding may sometimes be used as an ancillary feature 17 .

Alpha angle

The alpha angle is formed by the acetabular roof to the vertical cortex of the ilium. This is a similar measurement to that of the acetabular angle (see below). The normal value is greater than or equal to 60º.

The beta angle is formed by the vertical cortex of the ilium and the triangular labral fibrocartilage (echogenic triangle). The normal value is less than 55º  6 but is only useful in assessing immature hips when combined with the alpha angle.

Bony coverage (d:D ratio)

The percentage of the femoral epiphysis covered by the acetabular roof. A value of >50% is considered normal 7,14 .

Plain radiograph

A single AP radiograph is the most appropriate examination in children where femoral head ossification has occurred, e.g. over 1 year old. A frog-leg lateral view does not add additional information but does double the radiation dose 15 .

Asymmetry of the femoral head ossification center (delayed on the abnormal side) is often present. Determine the relationship of the proximal femur to the developing pelvis. The femoral head should be centered in the inferomedial quadrant defined by the intersection of Hilgenreiner line and Perkin line . Interruption of the Shenton line may also be evident.

The acetabular angle  should be <30° at birth and progressively reduce with the maturation of the joint to <22 at 1 year 16 .

The extrusion index is a percentage measure of bony coverage of the femoral head by acetabulum in patients with fully matured femoral epiphyses. A value of <25% has been reported as normal 11 . The greater the degree of acetabular dysplasia, the greater the extrusion index.

The center-edge angle (CEA) of Wiberg  may be used in younger children. An angle is formed by Perkin line and a line from the center of the femoral head to the lateral edge of the acetabulum where a value of <20° is considered abnormal but considered only reliable in patients >5 years of age.

Management options include:

Pavlik harness : usually for younger patients (less than 6 months of age)

closed reduction : usually for older patients after 1 year of age

open reduction (ORIF) : much older patients or if closed reduction is not successful 10

• 1. US Preventive Services Task Force. Screening for Developmental Dysplasia of the Hip: Recommendation Statement. Pediatrics. 2006;117(3):898-902. doi:10.1542/peds.2005-1995 - Pubmed
• 2. Graf R. The Diagnosis of Congenital Hip-Joint Dislocation by the Ultrasonic Combound Treatment. Arch Orthop Trauma Surg (1978). 1980;97(2):117-33. doi:10.1007/BF00450934 - Pubmed
• 3. Roposch A, Moreau N, Uleryk E, Doria A. Developmental Dysplasia of the Hip: Quality of Reporting of Diagnostic Accuracy for US. Radiology. 2006;241(3):854-60. doi:10.1148/radiol.2413051358 - Pubmed
• 4. Mary Ellen Avery. Avery's Diseases of the Newborn. (2005) ISBN: 9780721693477 - Google Books
• 5. Lane F. Donnelly. Pediatric Imaging. (2009) ISBN: 9781416059073 - Google Books
• 6. Omeroğlu H. Use of Ultrasonography in Developmental Dysplasia of the Hip. J Child Orthop. 2014;8(2):105-13. doi:10.1007/s11832-014-0561-8 - Pubmed
• 7. Brian D. Coley, John Caffey. Caffey's Pediatric Diagnostic Imaging. (2013) ISBN: 9780323081764 - Google Books
• 8. Sewell M & Eastwood D. Screening and Treatment in Developmental Dysplasia of the Hip-Where Do We Go from Here? Int Orthop. 2011;35(9):1359-67. doi:10.1007/s00264-011-1257-z - Pubmed
• 9. Wright J. Hip and Spine Surgery is of Questionable Value in Spina Bifida: An Evidence-Based Review. Clin Orthop Relat Res. 2011;469(5):1258-64. doi:10.1007/s11999-010-1595-y - Pubmed
• 10. Sanghrajka A, Murnaghan C, Shekkeris A, Eastwood D. Open Reduction for Developmental Dysplasia of the Hip: Failures of Screening or Failures of Treatment? Ann R Coll Surg Engl. 2013;95(2):113-7. doi:10.1308/003588413X13511609957137 - Pubmed
• 11. Chiamil S & Abarca C. Imaging of the Hip: A Systematic Approach to the Young Adult Hip. Muscles Ligaments Tendons J. 2016;6(3):265-80. doi:10.11138/mltj/2016.6.3.265 - Pubmed
• 12. Gulati V, Eseonu K, Sayani J et al. Developmental Dysplasia of the Hip in the Newborn: A Systematic Review. World J Orthop. 2013;4(2):32-41. doi:10.5312/wjo.v4.i2.32 - Pubmed
• 13. Landa J, Benke M, Feldman D. The Limbus and the Neolimbus in Developmental Dysplasia of the Hip. Clin Orthop Relat Res. 2008;466(4):776-81. doi:10.1007/s11999-008-0158-y - Pubmed
• 14. Harcke H & Pruszczynski B. Hip Ultrasound for Developmental Dysplasia: The 50% Rule. Pediatr Radiol. 2017;47(7):817-21. doi:10.1007/s00247-017-3802-4 - Pubmed
• 15. Hudak K, Faulkner N, Guite K et al. Variations in AP and Frog-Leg Pelvic Radiographs in a Pediatric Population. J Pediatr Orthop. 2013;33(2):212-5. doi:10.1097/BPO.0b013e31827e8fda - Pubmed
• 16. Starr V & Ha B. Imaging Update on Developmental Dysplasia of the Hip with the Role of MRI. AJR Am J Roentgenol. 2014;203(6):1324-35. doi:10.2214/AJR.13.12449 - Pubmed
• 17. Cheng E, Mabee M, Swami V et al. Ultrasound Quantification of Acetabular Rounding in Hip Dysplasia: Reliability and Correlation to Treatment Decisions in a Retrospective Study. Ultrasound Med Biol. 2015;41(1):56-63. doi:10.1016/j.ultrasmedbio.2014.08.007 - Pubmed

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Some results uranium dioxide powder structure investigation

• Processes of Obtaining and Properties of Powders
• Published: 28 June 2009
• Volume 50 , pages 281–285, ( 2009 )

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• E. I. Andreev 1 ,
• K. V. Glavin 2 ,
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• V. V. Malovik 3 ,
• V. V. Martynov 3 &
• V. S. Panov 2  

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Features of the macrostructure and microstructure of uranium dioxide powders are considered. Assumptions are made on the mechanisms of the behavior of powders of various natures during pelletizing. Experimental data that reflect the effect of these powders on the quality of fuel pellets, which is evaluated by modern procedures, are presented. To investigate the structure of the powders, modern methods of electron microscopy, helium pycnometry, etc., are used. The presented results indicate the disadvantages of wet methods for obtaining the starting UO 2 powders by the ammonium diuranate (ADU) flow sheet because strong agglomerates and conglomerates, which complicate the process of pelletizing, are formed. The main directions of investigation that can lead to understanding the regularities of formation of the structure of starting UO 2 powders, which will allow one to control the process of their fabrication and stabilize the properties of powders and pellets, are emphasized.

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Investigation of the Properties of Uranium-Molybdenum Pellet Fuel for VVER

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Assmann, H., Dörr, W., and Peehs, M., “Control of HO 2 Microstructure by Oxidative Sintering,” J. Nucl. Mater. , 1986, vol. 140,issue 1, pp. 1–6.

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Andreev, E.I., Glavin, K.V., Ivanov, A.V. et al. Some results uranium dioxide powder structure investigation. Russ. J. Non-ferrous Metals 50 , 281–285 (2009). https://doi.org/10.3103/S1067821209030183

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