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© 2000 The Journal of Bone and Joint Surgery, Inc.
Ultrasonography in Developmental Dysplasia of the Hip* 
*No benefits in any form have been received or will be received
from a commercial party related directly or indirectly to the subject
of this article. No funds were received in support of this study.
 A safe, noninvasive method of imaging of the hip: it can
be used both for diagnosis and to monitor treatment.
The use of ultrasonography to examine the neonatal hip was introduced and developed by Graf39. It soon became apparent that ultrasonography could provide images of the soft-tissue components of the infant hip - that is, the cartilaginous components of the femoral head and the acetabulum, the joint capsule, and the labrum. Novick et al.83 and Harcke et al.56 introduced multiplanar ultrasonography to study the infant hip in the coronal and transverse planes. Developmental dysplasia of the hip is a term used to describe an abnormal relationship between the femoral head and the acetabulum. We use this term to describe dislocation, subluxation and instability when it is possible to dislocate or locate the femoral head in the acetabulum, and a whole array of abnormalities that express inadequate acetabular development. There is now ample evidence that ultrasonography can play a major role in the detection and management of developmental dysplasia of the hip in children younger than one year of age. In Europe it is performed by orthopaedic surgeons, radiologists, and pediatricians, whereas in the United States it is generally performed by radiologists22,62. Most reports addressing the current role of ultrasonographic examination in the diagnosis and treatment of developmental dysplasia of the hip have been generated at large universities and in countries that have nationalized health services40,42,50,57,58,104. Not all communities have such services, and some orthopaedists may find themselves without access to this technique. In many communities in the United States, there are three systems - radiology-based, radiology and orthopaedic-based, and orthopaedic-office-based - for providing ultrasonography for the diagnosis of developmental dysplasia of the hip. Davids et al.22 reviewed the costs and benefits of each type of delivery system and found that, once expertise had been gained and start-up costs had been met, the orthopaedic-office-based system was the most convenient, cost-effective, and efficient, for patients, families, and treating physicians. This reflects the experience in other fields such as cardiology, obstetrics, and family medicine, in which the utility of office-based ultrasonography is widely recognized and the procedure has become standard22. Two methods of ultrasonography of the hip are currently in use: the static technique proposed by Graf39,40,45 and the dynamic method described by Harcke et al.56,57,59. The static method emphasizes morphology and classifies the status of the hip on the basis of angular measurements of the acetabulum41,45. The dynamic approach consists of a multipositional evaluation that resembles the physical examination. The ability of ultrasonographic examination to demonstrate abnormalities that are not detected clinically or radiographically, as a result of its ability to image the cartilaginous components of the infant hip, has been well established8,16,30,76,79,85,106. Ultrasonography has been recommended for the initial examination of infants who demonstrate abnormal clinical signs or who are at an increased risk for developmental dysplasia of the hip82. The use of ultrasonography for routine screening has also been studied, and some investigators have suggested that it should become part of the standard care for this condition. However, ultrasonographic screening may lead to overdiagnosis and overtreatment, and the extensive resources that are required for such a program have prevented its implementation in many areas of the world. In this article, the current use of ultrasonography in the diagnosis and management of developmental dysplasia of the hip is reviewed and unresolved issues concerning screening of newborns and ultrasonographic follow-up and assessment of the results of treatment are examined.
Diagnostic ultrasonography employs a transducer that functions as a transmitter and a receiver of acoustic energy. Ultrasonography of infant hips employs a real-time scanning technique, in which ultrasonographic pulses are transmitted into the body and are received rapidly enough so that the movement of mobile anatomical structures can be seen directly. Ultrasonography should be conducted with a real-time scanner in which images change quickly enough to permit observation of motion and to facilitate multiple examinations of the hip joint58. Ultrasonography offers distinct advantages compared with other imaging techniques. First, unlike plain radiography, it can distinguish the cartilaginous components of the acetabulum and the femoral head from other soft-tissue structures. Second, real-time ultrasonography permits multiplanar examinations that can clearly determine the position of the femoral head with respect to the acetabulum; thus, it provides the same type of information that can be obtained with arthrography, computerized tomography, or magnetic resonance imaging, but at lower cost. Third, although ultrasonography is more expensive than plain radiography, it does not require sedation and does not involve ionizing radiation. Fourth, unlike other techniques, it allows observation of changes in hip position with movement26,36,37. Several types of transducers, including the linear, sector, and curved-faced types, can be used. Although sector or curved-faced transducers can visualize a dislocated hip, geometric distortions can lead to diagnostic errors, particularly with regard to a dysplastic hip. Because of the low reproducibility of measurements obtained from sector scanners, the hip joint cannot be quantitatively assessed satisfactorily with that instrument29,46. Current quality-assurance requirements demand the use of linear transducers47. The use of sector or curved-faced transducers should be limited to qualitative evaluation. Thus, measurements of hip morphology should be made only on images produced with linear transducers47,61. Real-time linear-array transducers are preferred for the assessment of hips in newborns and infants. With the use of currently available linear-array transducers, highly reproducible images can be generated, allowing serial static quantitative assessment of hip development and maturation42,44,45,54,98,100 as well as serial semiquantitative assessment of stability16,56-58,76,77,87,91,97. The highest-frequency transducer that is able to provide sufficient depth to image the medial aspect of the acetabulum should be used. A frequency of 7.5 megahertz is best suited for infants up to one month of age, while 5.0 megahertz is best for infants between one month and one year of age, when the ossification center is usually quite large and inhibits visualization of acetabular landmarks52,61. The ultrasonographic study should be recorded as a hard copy on film or on a videoprinter to provide a permanent record of the examination. A high-quality pictorial record, with images obtained in standard planes, is required to obtain a correct, complete, and reproducible evaluation on the basis of the recorded image. Computerized systems with software to digitize the video ultrasonogram can be used to reformat the video image in order to accentuate certain anatomical structures.
Graf et al.39,40,44,45,48 introduced the in-depth use of hip ultrasonography with the evaluation based on a coronal image obtained through a lateral approach when the infant is in the lateral decubitus position. Stressing morphological characteristics, his method emphasized measurements of angles to quantitate femoral head coverage on the basis of acetabular landmarks, in addition to the assessment of hip position. In contrast to the single-view approach, Harcke et al.56,57,61 developed a technique based on a dynamic multiplanar examination that assesses the hip in positions produced by the Ortolani84 and Barlow5 maneuvers. The dynamic approach can also be used to assess acetabular development; however, it places the greatest emphasis on the position and stability of the femoral head. Critics of Graf's morphological technique have reported limitations with regard to its accuracy as well as interobserver and intraobserver variations that influenced the analysis15,25,28. Advocates of Graf's method believe that, when it is performed properly, the variability in measurement is not an important factor and standardization is easier to establish47,54,55,82. Critics of the dynamic technique maintain that it is more prone to subjectivity on the part of the examiner and that standardization is more difficult to establish20,38,49. Advocates of dynamic ultrasonography have pointed out that traditional clinical examinations are based on criteria of stability in addition to morphological characteristics28,57,58,61,88,89. Regardless of the method that is used, proponents of ultrasonography consider it to be more sensitive than clinical examination79,103. Comparison of ultrasonographic examination with standard physical examination revealed that both dynamic16,38 and morphological studies8,105 identified abnormalities of the hip that were not detected clinically. By allowing earlier detection, ultrasonography lowered the number of surgical interventions and led to a high reduction rate with a minimum of iatrogenic complications30,47,55,82,103. More recently, in an ultrasonographic study of 8530 newborns, Graf47 indicated that the static and dynamic approaches should be used concomitantly. In 1993, Harcke, Graf, and Clarke60 merged their methods and proposed a Dynamic Standard Minimum Examination, which combined morphological and stability criteria. The principles of this examination mandate that the hip be examined both at rest and when stressed. Assessment should include views in two orthogonal planes26,37,49,61. The essential elements of the Dynamic Standard Minimum Examination are assessment in the coronal plane with the hip at rest and assessment in the transverse plane with the hip under stress. With regard to the specifics of these elements, some options are left to the preference of the examiner. It should be noted that the measurement of acetabular characteristics, such as angular measurement of acetabular landmarks, is considered optional61.
Graf's technique of static measurement relies most on the morphological appearance of the cartilaginous acetabulum. The static technique is performed with the infant in the lateral decubitus position and the hip in 35 degrees of flexion and 10 degrees of internal rotation. Morphology is assessed by describing basic anatomical features and by angular measurement. The dynamic hip examination is performed following an examination of the hip at rest. The hip is checked for instability, which can be quantified by measurement of the degree of displacement of the femoral head. The infant lies on his or her side in the positioning apparatus, and the transducer is positioned over the hip, which is then adducted and pushed superiorly to demonstrate instability. The ultrasonographic findings are graded as so-called hip types41-46, according to the development of acetabular ossification (Table I). Angular measurements serve to confirm the diagnosis indicated by the morphological description and provide a quantitative parameter for comparison of findings48 (Fig. 1).
A coronal image of the hip is obtained, and three lines are constructed: a vertical line drawn parallel to the ossified lateral wall of the ilium; a line drawn along the roof of the cartilaginous acetabulum, from the lateral osseous edge of the acetabulum to the labrum; and a line drawn from the inferior edge of the osseous acetabulum (the inferior iliac margin) at the roof of the triradiate cartilage to the most lateral point on the ilium (the superior osseous rim). Two angles are calculated. The a angle (Fig. 1) is formed by the intersection of the line parallel to the lateral wall of the ilium and the line parallel to the osseous acetabulum. A reference for normal values - that is, the mean and range of the a angle - has been established. The lower limit of normal for the a angle is 60 degrees48. Furthermore, a maturation curve of spontaneous development has been established to characterize the measurement of the natural progression of acetabular growth in the normal hip joint48,106. Because the a angle reflects osseous coverage of the femoral head by the acetabulum, the smaller the angle the greater the degree of dislocation. The b angle (Fig. 1) is formed by the intersection of the line parallel to the lateral wall of the ilium and the line parallel to the roof of the cartilaginous acetabulum. A b angle of more than 77 degrees indicates eversion of the labrum and subluxation of the hip48. The position of the head of the femur is irrelevant to the ultrasonographic evaluation of the acetabulum. The difficulty in determining the exact topographic orientation of the individual plane of ultrasonographic section must be considered a drawback. It may be difficult to determine whether the acetabulum has been visualized in an oblique plane or in the correct frontal orientation. Only a reproducible frontal-plane section clearly showing the inferior iliac margin, the osseous acetabular promontory, and the acetabular labrum is suited for the recognition of the landmarks and the drawing of the lines. For these reasons, a standard plane for obtaining angular measurements was defined as a strictly frontal plane of section through the acetabular fossa. A positioning device, molded to accommodate the torso, pelvis, and legs, is very helpful for placing the infant in the desired, comfortable position and for obtaining optimal and reproducible images. The hip is then classified into one of four main types according to Graf's classification41-46 (Table I). This classification is based on the degree of femoral head displacement and the associated deformation and growth retardation of the acetabular roof. With the static technique, emphasis is placed on dysplastic changes of the hip (the acetabular osseous roof and rim and the cartilaginous roof) rather than on hip instability. Type I indicates a normal hip with a good cartilaginous and osseous roof (an a angle of 60 degrees or more) (Fig. 1). Type IIa represents an immature hip in an infant who is younger than three months of age, with delayed ossification but an adequate cartilaginous roof and an a angle of 50 to 59 degrees. Type IIb refers to a hip with delayed ossification in an infant more than three months of age, with a rounded, osseous acetabular promontory; an a angle of 50 to 59 degrees; and a b angle of more than 55 degrees (Fig. 2). Types IIc, D, III, and IV are always pathological. In types D, III, and IV, the bone-molding of the acetabulum is severely deficient or poor and there is lateralization of the femoral head (Fig. 3 and Fig. 4). The a angle is 43 to 49 degrees in types IIc and D and less than 43 degrees in types III and IV. The b angle is 70 to 77 degrees in type IIc and more than 77 degrees in types D, III, and IV. The cartilaginous acetabulum is displaced superiorly and is ultrasonographically dense in type IIIb. The cartilaginous acetabulum is interposed between the femoral head and the ilium in type IV. Testing for functional instability should be performed for hips with types IIc through IV. These hip types exhibit moderate-to-extreme deficiency of bone-molding of the acetabulum. Dynamic testing for instability can provide the treating physician with clinically important information on hips that are poorly developed but do not clearly exhibit the Ortolani sign84.
The technique of dynamic hip ultrasonography incorporates motion and stress maneuvers that are based on accepted clinical examination techniques56,83. The multiview dynamic assessment emphasizes hip position and stability, but it also includes an assessment of acetabular development. It has been found to be effective in the initial detection of infant hip abnormalities and in monitoring treatment57. There are several variations and modifications of this technique10,20,38,74,96. It is possible to reduce the extent of the examination yet theoretically to obtain the same information57,63. Ultrasonographic examination permits classification of the positional relationship of the femur to the acetabulum with the hip at rest and under stress. With the dynamic method, an attempt is made to visualize the Barlow and Ortolani maneuvers on the ultrasonography screen. The technique is dependent on ligamentous or capsular laxity, and, as with the physical examination, the study quality depends on the operator performing the stress test. In a normal hip, the femoral head is well positioned and stable under stress. In the first few weeks of life, the femoral head is reduced in the acetabulum at rest, but it may show slight displacement (physiological laxity) under stress; this should resolve by the time that the infant is four weeks of age1,2,4. Subluxation implies displacement of the head from the acetabulum; however, the head is not completely dislocated. In more severe forms of hip dysplasia, the femoral head may be dislocated from the acetabulum at rest or it may be displaced by means of maneuvers60. When the femoral head is completely dislocated, fibrofatty tissue with increased echogenic properties fills the space between the head and the acetabulum. The lateral approach for ultrasonography has been the most widely accepted52,105. This approach allows the hip to be studied in orthogonal projections and hip motion to be visualized easily during stress maneuvers. It also allows assessment of the hip during treatment with a Pavlik harness. Four basic lateral views were described by Grissom and Harcke52. The choice of the view depends on factors such as the preference of the ultrasonographer and the clinical status of the infant. The views are coded with use of a two-word combination that reflects the transducer orientation (coronal or transverse) with respect to the hip and the position of the femur (neutral or flexed). At a minimum, the examination should consist of two orthogonal views with one obtained during a stress maneuver62. The dynamic technique is performed with the infant in both the lateral decubitus and the supine position, and imaging is carried out in the coronal and transverse planes both with and without stress (Fig. 5-A and Fig. 5-B). The coronal image is obtained with the hip flexed to 90 degrees as posterior stress is applied to the knee with the palm of the hand (the Barlow provocative test). Any resultant subluxation is then noted. It should be remembered that four to six millimeters of subluxation is normal during the first few days of life2,75. If the hip subluxates or dislocates (Fig. 5-C), reduction is attempted (the Ortolani maneuver). The second stage of the dynamic method consists of similar imaging in the transverse plane and visualization of the position of the femoral head with respect to the triradiate cartilage of the acetabulum. Measurement of acetabular landmarks (angles and coverage) is optional, and either the neutral or the flexion view in the coronal plane can be used. The configuration of the acetabulum can also be assessed with use of morphological criteria61.
The morphological technique provides information related to the development of the femoral head and the acetabulum. These key anatomical structures can be visualized by ultrasonography from the time of birth, even though the proximal part of the femur and much of the acetabulum are composed of cartilage. The configuration of the osseous and cartilaginous acetabulum is measured and is used as the basis for assessing development43. Development of the ossification center of the femoral head is an important landmark recognized between the second and eighth months of life. The ages at which the ossification center normally appears range widely, and it typically develops earlier in girls. The femoral ossification center is detected on the ultrasonogram before it is visible radiographically. With maturation, the ossification center increases in size until it becomes large enough to obscure the echoes from the inferior iliac margin at the medial part of the acetabulum111. Because of the maturation process, the real-time scan is not capable of demonstrating details of the key anatomical landmarks, and when the child is approximately one year of age it loses its advantage compared with plain radiography for the recognition of anatomical structures26,37,52.
With the expanding use of ultrasonography, increased emphasis has been placed on technical issues, such as the quality of the images that are obtained and the ability to reproduce and analyze them. Image repeatability and reliability were examined by Jomha et al.70, who concluded that the morphologically and dynamically based methods were reproducible with training and frequent use. Harcke's guidelines62,63 have a wide equivocal zone for clinical evaluation and judgment as his method involves an attempt to visualize the results of stability tests, perhaps limiting its clinical usefulness. Graf's classification41-46 of hip types (Table I) gives a better indication of the normal and pathological states of the infant hip. Dias et al.25 evaluated interobserver and intraobserver agreement with regard to the interpretation of static ultrasonographic images. The measurement of the a angle had only a fair degree of reproducibility both between different observers and between different evaluations by the same observer. The range of interobserver measurements of the b angle was much wider than was the range of intraobserver measurements of that angle. Dias et al. believed that dynamic real-time scanning would add valuable information to the static images. Of the static measurements, such as the a and b angles and the percentage of femoral head coverage, the a angle has been found to provide the most reliable measurement15. When observers examined the same ultrasonographic strip in the study by Bar-On et al.6, intraobserver agreement concerning the Graf classification was substantial but interobserver agreement was only moderate. The reliability of morphological as well as stability criteria was studied by Rosendahl et al.95. Morphology was classified according to the subjective assessment of the examiner or the objective measurement of the acetabular inclination angle (the a angle), or a combination of the two, into four categories: normal, immature, minor dysplastic, and major dysplastic. Interobserver and intraobserver agreement was determined for the interpretation of recorded ultrasonographic scans and for a comprehensive examination (recording as well as interpretation of the scans). The hip was classified subjectively as stable, unstable, dislocatable, or dislocated. There was a high degree of agreement concerning the morphological classifications based on repeated interpretations of recorded scans by the same observer, but the degree of agreement between observers was moderate. The intraobserver agreement for repeated interpretations and recordings was moderate when the interpretation was based on a subjective classification. The addition of the a angle did not improve agreement. There was moderate interobserver agreement in determining hip stability. Rosendahl et al. concluded that there can be a high degree of interobserver and intraobserver agreement in the classification of hip morphology on the basis of recorded ultrasound scans. Interobserver and intraobserver agreement in producing the scans is poorer than it is for interpreting them. To obtain a high degree of interobserver agreement in the assessment of hip morphology and stability in the newborn, substantial training and attention to detail are necessary when performing the technique and evaluating the results.
The clinical tests of Barlow5 and Ortolani84 are conventionally used in screening for developmental dysplasia of the hip in the neonate. Despite early optimism about the effectiveness of these procedures, their specificity and sensitivity have been questioned78. There has been no change in the prevalence of developmental dysplasia of the hip that is diagnosed late, despite rigorous clinical screening procedures, and it is not clear whether clinical screening alone can reduce the prevalence19. It is now believed that a range of conditions affecting the hip may be diagnosed during the first few months of life. These conditions range from an established dislocation that is irreducible at birth (and that is often missed) to simple hip instability, which usually resolves without treatment. An important group of conditions within this range are those in which the hip is eccentrically placed; these hips may progress to acetabular dysplasia with subluxation, although some cases may be no more than normal variants44,45,47,48,105. An important issue is whether ultrasonographic screening of newborns for developmental dysplasia of the hip is justified on the basis of the degree of sensitivity, specificity, and cost-effectiveness. Bialik et al.9 recommended that ultrasonographic examination be performed for all newborns. Some European centers screen all newborns30,33,105; an alternative approach is to perform scanning only when a newborn is at risk as determined by the history or the physical examination18,37,71,72,93,94,108. Ultrasonography is very useful for the detection of developmental dysplasia of the hip and can demonstrate abnormalities not found on clinical examination8,13,40,58,104. Some centers are currently using real-time scanning to screen all newborns28,29,98,99,102. This may be appropriate in certain geographic areas, such as central Europe and northern Italy, where the prevalence of hip dislocation is high. However, in North America, ultrasonography is more often used to screen selectively3,31,32. Marks et al.79 reported the results of a policy of ultrasonographic examination of all infants at the time of birth. Of 14,050 infants, 6 percent (847) had abnormal scans, but 90 percent of the 847 had normal scans by the time that they were nine weeks of age. All infants with a clinically abnormal hip had an abnormal initial ultrasonographic examination. Five infants who were not diagnosed by clinical examination and who had no risk factors had an abnormal ultrasonographic study and were subsequently found to have a clinically abnormal hip. Treatment was required for fifty-nine hips (2.42 per 1000); thirty-seven (1.5 per 1000) were treated because of persistent clinical instability and twenty-two (0.85 per 1000), because of persistent ultrasonographic abnormalities. The latter figure is very similar to that for late-diagnosed cases reported in other studies18,19. Hip ultrasonography performed at birth is therefore capable of detecting nearly all abnormal hips79. No hip that was studied by ultrasonography and found to be normal at birth became abnormal with time79, although there was still the possibility of very late development of dysplastic changes14. These results are similar to those reported by Boeree and Clarke11, who used delayed selective ultrasonographic screening to complement neonatal clinical screening. Of 26,952 infants, 1894 were referred for secondary screening because of a clinical abnormality or the presence of a risk factor (breech delivery11, either vaginal or by cesarean section; postural or structural foot deformity11; a positive family history for developmental dysplasia of the hip11; torticollis; or oligohydramnios). Treatment was required for only 118 infants (4.4 per 1000 births). Of the infants who were referred with clinical instability, 35 percent did not require treatment. Dislocation or subluxation was detected in seventeen of 643 infants who were referred only because of risk category; all seventeen had a normal clinical examination. Six infants presented with developmental dysplasia of the hip after they were twelve weeks old (a late-presentation rate of 0.22 per 1000 births). All had normal findings on clinical examination within twenty-four hours after birth, and none were in a high-risk category. Ten infants required surgery (a surgical treatment rate of 0.37 per 1000 births)11. Andersson and Funnemark1 used the anterior-dynamic method for the screening of 4430 children. The frequency of treatment for unstable hip joints was reduced to 0.18 percent compared with 1.7 percent without ultrasonographic screening. Those authors thought that anterior-dynamic ultrasonography could optimize the results of screening in many clinics2. Many investigators have advocated the routine use of ultrasonography to screen all neonates for developmental dysplasia of the hip or to evaluate those who are at increased risk5,13,16-18,38,44,57,71,72,102,105,108; however, the routine screening of all newborn infants is still controversial58. The fact that ultrasonography does not pose a physiological hazard does not mean that the procedure is without cost. The direct costs of purchasing and maintaining the equipment, training the examiners, and taking the time necessary to perform routine screening have a considerable impact on the cost to the individual and to society66. Selective screening of high-risk infants has been advocated as a more practical alternative18,71,72,108; however, opinions differ as to whether this approach can substantially reduce the prevalence of late-presentation and late-diagnosed cases18,72. It is very difficult to draw conclusions from data obtained from relatively small series compared with the large central European experience4,7,23,27,29,33,65,68,69,76,86,90-92,101,102,105,109. In Europe, ultrasonographic screening replaced a very meticulous clinical and radiographic screening program carried out in health-care programs supported by third-party payers. This may explain the diversity among the results and recommendations of the various studies. Clarke et al.18, Berman and Klenerman8, as well as Andersson and Funnemark1 compared ultrasonographic with clinical findings and found ultrasonography to be a more sensitive diagnostic tool, but it may be too sensitive because it also identifies clinically unimportant instability. Castelein et al.14 reported on 144 hips that had ultrasonographic evidence of abnormalities although they were clinically normal. None were treated, and after six months four (3 percent) had developmental dysplasia. Three of these four hips had risk factors. Gardiner et al.34 reported that abnormalities seen on neonatal ultrasonograms resolved rapidly, and they questioned whether ultrasonography could predict the need for treatment in the neonatal period. Several investigators have focused on infants who are at higher risk for developmental dysplasia of the hip and have implemented limited ultrasonographic screening programs94,108. Clarke et al.18 carried out a selective screening program in which high-risk infants had ultrasonographic in addition to clinical examination. Those authors concluded that selective screening would not reduce or eliminate the number of cases that were diagnosed late. Boeree and Clarke11, as mentioned earlier, reported on a combination of clinically and ultrasonographically based methods of diagnosis for an at-risk group. They found that only 7 percent of 26,952 infants required screening at a special clinic and only 6.2 percent (118) of them (4.4 per 1000 live births) needed treatment. Nevertheless, they reported a late-presentation and late-diagnosis rate of 0.2 per 1000. Ultrasonographic screening of the high-risk groups reduced the prevalence of late-diagnosed cases but only to the level reported after thorough clinical screening of all infants11. On the basis of a comparison of clinical screening and ultrasonographic screening, Tönnis et al.105 concluded that all newborns should be screened with ultrasonography because more disorders are detected with that modality. Marks et al.79, in a study of 14,050 infants, observed that the prevalence of developmental dysplasia of the hip (0.6 per 1000) found by ultrasonographic screening of newborns who had normal findings on clinical examination at birth was similar to the prevalence of late-diagnosed developmental dysplasia without ultrasonographic screening. Since the establishment of ultrasonographic screening, no late case of developmental dysplasia of the hip had presented for treatment in a baby born in their community. Eight hundred and forty-seven infants (6 percent) had ultrasonographic evidence of abnormalities on the first scan; of these, approximately 78 percent (657 infants) had a normal scan by the fourth week and 90 percent, by the ninth week. This finding emphasizes the need to avoid overtreatment. Of the infants with abnormal ultrasonographic findings on the first examination (within the first three weeks after birth), only 2.6 percent had a clinically abnormal hip on physical examination. The treatment rate was 2.42 per 100079. The clinical utility of ultrasonographic screening remains uncertain. Most investigators who have reported the implementation of selective or mass ultrasonographic screening have found clinically silent hip dysplasia and have concluded that the addition of ultrasonography to clinical screening would help to detect more children with developmental dysplasia of the hip. The experiences of Graf et al.48 and Marks et al.79 further suggest that all children with developmental dysplasia of the hip may be identified if widespread screening is used. Hernandez et al.67 used a cost-based decision analysis and concluded that ultrasonography is not a valuable screening tool if the severity of the disorder and the cost of screening are considered. There are other problems with ultrasonographic screening programs aside from cost. These include the need for well equipped facilities, expert ultrasonographers, and standardization of the examination. One negative aspect of ultrasonographic screening of all newborns is that the technique leads to several repetitions of clinical and ultrasonographic examination for a substantial percentage of the population. Another criticism of such screening is the high number of infants who are treated as a result of screening102. Rosendahl et al.93, in a study of 1503 newborns, attributed the high prevalence of infants treated in their series (ninety-two; 31.2 per 1000) to the inclusion of ultrasonography in the screening program. Vedantam and Bell107 reported on the selective ultrasonographic screening of 7827 newborns: 114 who had clinical abnormalities or were at high risk for developmental dysplasia of the hip were screened. The treatment rate was 3.9 per 1000, which was comparable with the rate of 3.7 per 1000 reported by Clarke et al.18. This rate was lower than the rate of 10.8 per 1000 reported by Jones and Powell72 in a prospective study in which there were ninety-eight abnormal hip ultrasonographic findings in 406 babies from a birth population of 3879. In a study of 1310 infants who were examined with the Ortolani and Barlow tests as well as 2587 who were examined with ultrasonography, Tönnis et al.105 found that twice as many infants were treated after ultrasonographic screening. The evidence to date has not proved that selective screening of newborns would prevent all late-diagnosed cases of developmental dysplasia of the hip. The 0.12 per 1000 prevalence of late-presentation and late-diagnosed cases of developmental dysplasia of the hip reported by Vedantam and Bell107 was lower than the 0.68 per 1000 prevalence reported by Clarke et al.18, but it was not comparable with the prevalence of zero reported by Jones and Powell72. The value of selective screening, with use of dynamic as well as morphological methods, for infants with risk factors was studied by Paton et al.85, in a population of 20,452 infants. Those authors confirmed that risk factors alone had a relatively poor predictive value if used to screen for dislocation. Among infants who had been referred because of clinical instability, one of every eleven who were screened (95 percent confidence interval, eight to seventeen) had a dislocation; among those who had been referred because of the presence of any of the major risk factors, the prevalence was one in seventy-five (95 percent confidence interval, forty-two to 149). Routine ultrasonographic screening of all infants in the at-risk groups just because they had risk factors was of little value in reducing the rate of late-diagnosed dysplasia of the hip, but ultrasonographic examination of all clinically unstable hips whether or not there were associated risk factors led to a high rate of detection85. The timing of the screening is another debatable point. Screening of infants who are six weeks old, for example, identifies persistent abnormalities early but allows minor abnormalities that otherwise would have necessitated a follow-up examination to resolve in the period immediately after birth. The disadvantage of late screening is that it is difficult to ensure that the entire population is examined58. An important issue is whether the sensitivity of ultrasonography leads to unnecessary treatment. Ultrasonography identifies acetabuli that are morphologically immature43, creating the potential for overtreatment106. Some studies have indicated that not all such infants need treatment, and there is currently a dilemma concerning whom to treat and when13,17,29,76,111. If ultrasonographic evidence of laxity or a morphological deficit persists in an infant who is older than four weeks and has a clinically stable hip, the orthopaedic surgeon must decide whether to continue to observe the patient or to initiate treatment. Currently, most physicians agree that minor abnormalities can be observed without treatment and that the patient should be examined with ultrasonography at four-week intervals to document resolution of the problem58. It can also be argued that treatment of large numbers of infants produces some complications that may equal or outweigh the benefit of improved detection. Gardiner and Dunn35, however, did not find a single case of avascular necrosis in a series of seventy-nine infants who were treated with a splint and monitored with ultrasonography. A number of large series of prospective ultrasonographic screenings for developmental dysplasia of the hip have been reported from countries in central Europe. The collective data included in these studies generated information on a total of 124,332 hips that were examined with use of the Graf method4,8,23,24,27,29,33,65,67,69,76,86,90-92,101,102,105,109. Although the studies were done on an unselected neonatal population and were performed and analyzed by different authors in various countries, hospitals, and clinics4,23,27,33,68,69,76,86,91,93,105, some conclusions can be drawn. In all of these reports, a very small group of hips was classified as pathological on the first ultrasonographic examination. A much larger group of hips was classified as immature, with a physiological delay in ossification but an adequate cartilaginous acetabular roof, and was designated as warranting repeated ultrasonographic follow-up examination. The cumulative European data supports the concept of using ultrasonography to diagnose developmental dysplasia of the hip. The high number of immature hips in neonates makes the screening program inefficient, and follow-up examinations are mandatory in this group. However, most of these hips will show spontaneous development and maturation. Therefore, the most appropriate age for an ultrasonographic hip-screening program is approximately four to six weeks, not during the first week of life. Ultrasonographic screening seems to have a very favorable effect upon the results and duration of treatment when it is carried out routinely in an unselected patient population47,48,105. In such cases, the age at which treatment was begun was advanced from the twentieth to the tenth week of life. The end of treatment also was advanced, from the forty-eighth to the thirty-sixth week. Graf47 found that all hip joints that needed treatment were identified within the first six weeks of life. Clinical and radiographic follow-up examination showed that the average age at the end of treatment of dislocated and dysplastic hips was 4.5 months. All joints were effectively treated without surgical intervention. Since the initiation of the newborn screening program in 198747, not a single case of avascular necrosis of the femoral head was detected. This low rate was attributed to the early detection of dislocated hips, which were treated with a Pavlik harness and did not later require closed or open reduction. Since 1987, all hip joints had a normal center-edge angle on completion of treatment. Early detection and treatment were credited for the better results.
The use of ultrasonography in the management of patients with developmental dysplasia of the hip has focused on evaluation of the effectiveness of abduction devices21,51,53,64,87. When a diagnosis is established, the treatment that is prescribed and the mode of follow-up that is chosen depend on the age of the child and the severity of the abnormality. Ultrasonography seems to be most accepted as the standard modality for an initial, baseline evaluation of an unstable or dislocated hip. This baseline assessment is followed by serial ultrasonograms as clinically indicated over the course of nonoperative treatment with an abduction device. Physiological delay of ossification in an immature hip and mild instability in a child less than three months old should be followed with ultrasonograms every one or two months to confirm that the hip has matured and has attained the normal range of motion and that additional treatment is not indicated. When marked instability or dislocation is detected55,64, follow-up ultrasonograms to assess the response to treatment are made every three to four weeks for children who are less than three months old and every six weeks for those who are more than three months old. Ultrasonography should be used more frequently in the course of treatment of dislocation or subluxation (Graf types IIc through IIIb) than in that of dysplasia (type IIb). Follow-up after completion of treatment is performed every three months during the first year of life. Taylor and Clarke103 concluded that ultrasonographic monitoring led to an acceptably low level of intervention, a high rate of reduction, and minimal iatrogenic complications. The treatment rate averaged only 5.1 per 1000 live births over seven years. The rate of late presentation (missed by the screening program and not treated with the Pavlik harness) was 0.26 per 1000 live births. Those authors concluded that ultrasonographic assessment and monitoring of treatment for developmental dysplasia of the hip, irrespective of its screening value, facilitates treatment, reduces complication rates, and may result in a lower rate of late acetabular dysplasia103. Ultrasonography is extremely useful during treatment with a Pavlik harness51,53,54,58,73,87,110. Static coronal and transverse images can be obtained, usually with the harness in place. The resolution of the hip pathology during treatment can be documented, or alternative treatments can be chosen if there is no improvement in the stability or resolution of the dysplastic changes of the hip. Hangen et al.55 compared Pavlik harness therapy with and without ultrasonographic monitoring for the treatment of developmental dysplasia of the hip. The age at the time of diagnosis was similar in the two treatment groups. Treatment failure was recognized earlier in the group being monitored with ultrasonography. Ultrasonography was exceptionally useful in identifying hips that did not reduce or stabilize with harness treatment. The total number of radiographs was decreased in the group that was followed with ultrasonography. The use of ultrasonography also resulted in a shorter duration of treatment, providing a clearer end point for determining when a hip was normal and treatment could be discontinued. The a angle and the percentage of femoral head coverage were found to be the most accurate measurements for sequential examinations55. Dynamic ultrasonography has been tested as a way of monitoring the hip position of infants in a harness. The examination determines the stability of the hip within the limits of the harness, and it can be used to assist in the adjustment of these devices. When a dislocatable hip is treated with a harness, the restraint device maintains the hip in flexion and abduction. For this reason, the ultrasonographic examination is limited to transverse and coronal views made with the hip in flexion51. Both the transverse view with the hip in neutral and the stress view in the coronal plane with the hip in flexion are eliminated. The stress examination is done at the conclusion of treatment. Hip ultrasonography can be repeated frequently, and it has generally replaced radiography for the monitoring of treatment52. It has been recommended that a radiograph be made at the conclusion of treatment, to document osseous acetabular development and to serve as the baseline for orthopaedic follow-up61,87. Radiography is more helpful for children who are older than one year, although some authors have found ultrasonography to be useful for children who are as old as two years11. One of the problems associated with follow-up ultrasonography has been its lack of reliability for morphological assessment of the acetabulum28,81,111. The ultrasonographic and radiographic appearances of the osseous acetabulum do not always correspond80. Some of this discrepancy is related to variations between observers. When ultrasonography is used in conjunction with an occasional radiograph, the total exposure to radiation during the course of treatment is reduced58,64,87.
The cost of an ultrasonographic examination of the hip is an important consideration because it is more expensive than radiography. Any program must weigh the costs of identifying the condition, the investigation itself, and the consequences of missing cases that will be diagnosed later. Ultrasonographic examination is highly operator-dependent, and the technique of performing the examination and the interpretation of the image may influence the result. Compared with other organ systems, the hip requires considerably less time for examination with ultrasonography, and this justifies a reduction in the charges. The direct costs of purchasing and maintaining the equipment, training examiners to become proficient, and taking the time necessary to perform the procedure have a considerable impact on the cost to the individual and society when ultrasonography is used for routine screening22,26,67,68. In 1992, a general national ultrasonographic neonatal hip-screening program was instituted in Austria, with the costs being borne by the Austrian social welfare system50. The data from that program, which mandated a clinical examination and one ultrasonographic examination of each newborn, clearly demonstrated the cost-effectiveness of the program. After compiling and reviewing the published data, Hernandez et al.67 concluded that ultrasonography is not the preferred strategy for the screening of neonates and that its role in evaluating high-risk patients depends on the orthopaedic surgeon's point of view. Davids et al.22 analyzed financial and professional considerations and found that the private-practice use of ultrasonography in the diagnosis and management of pediatric hip dislocation is justified only when the volume of cases is high enough that the screening can be done at reasonable cost to the practice and can provide an adequate base for maintaining proficiency. If these criteria cannot be met, it is preferable that the pediatric orthopaedist and the hospital-based ultrasonographer maintain a mutually cooperative atmosphere in which children can be evaluated in a timely fashion. The decreased overall cost of treatment following the implementation of routine ultrasonography was confirmed by Swiss investigators12.
Ultrasonography of the infant hip can be used for both the diagnosis of developmental dysplasia and the monitoring of treatment. Ultrasonographic examination of the hip has definite advantages when it is combined with clinical examination. It can provide an assessment of the position, stability, and morphology of the hip until the child is one year old. Ultrasonography has been accepted by many as being more sensitive than clinical examination. Its reliability has been documented in many reports, and it has been suggested that it could be a substitute for radiographic examination in the first year of life. Ultrasonography has proved to be a safe, noninvasive method for imaging the hip. Therefore, it can be used to resolve the dilemma of whether to treat an unstable hip with a splint immediately or to delay treatment in the hope that the instability or the maturation deficit will resolve spontaneously. A consensus has not been reached concerning the best age for ultrasonographic screening. Many hips in children less than six weeks old have an immature appearance and require follow-up studies. Although the majority of immature hips are not dysplastic, ultrasonography cannot differentiate immaturity from early developmental dysplasia. Therefore, neonatal ultrasonographic examination identifies a large number of intermediate hips that require follow-up. This adds to cost as well as to parental anxiety. It is generally accepted that hip ultrasonography when a child is four to six weeks of age provides a more accurate indication of hip abnormality, as most transient instability or physiological immaturity, such as a delay in acetabular ossification in the presence of a good cartilaginous roof, has resolved by then. Also, these children are still young enough for treatment and intervention to be implemented if necessary. In addition, some cases of developmental dysplasia of the hip are detected that may not have been identified in the neonatal period. Used selectively, hip ultrasonography is clearly indicated for all infants with abnormal findings on clinical examination and for those with risk factors for developmental dysplasia. The mode of ultrasonographic follow-up depends on the age of the child and the severity of the abnormality. Neonates with abnormal findings on physical examination need immediate attention, with referral to an orthopaedic surgeon. Neonates with a hip click or equivocal findings on physical examination should be evaluated when they are four to six weeks old if these findings remain unchanged. Infants with risk factors should be screened with ultrasonography when they are four to six weeks of age, even if the findings on physical examination are normal. Note: The authors thank Prof. H. T. Harcke and Prof. R. Graf for their helpful comments and advice regarding the ultrasonographic screening policies in Europe and the United States.
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Introduction
Real-Time Ultrasonography
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