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Developmental Dysplasia of the Hip: Imaging
Updated: Sep 23, 2009
Radiography
Findings
Plain radiographs of the pelvis are most helpful when significant ossification of the capital femoral epiphyses has occurred and when adequate US evaluation cannot be performed. Plain radiographs of the pelvis are obtained in the frontal projection with the legs in the neutral position. Before the femoral heads begin to ossify, the projected locations must be estimated.
Line measurements made on the anteroposterior radiograph help in determining the relationship of the femoral head with the acetabulum (see Image 1).
Frontal radiograph of the pelvis. The ossification centers of the capital femoral epiphyses are symmetric and located in the joint spaces. Both heads project in the inner lower quadrants formed by the intersection of the Hilgenreiner (H) and Perkin (P) lines. Shenton lines (S) are continuous and demarcated by the dashed lines. The acetabular angles are symmetric and less than 28° bilaterally.
- The acetabular angle is determined by first drawing the Hilgenreiner (or Y-Y) line, which is a horizontal line between the 2 triradiate or Y-Y cartilages, and then drawing a second line connecting the superolateral and inferomedial margins of the acetabular roof, as Kirks and Griscom reported.19 The normal acetabular angle is approximately 28° at birth. The angle decreases gradually with age as a result of modeling of the acetabulum by the femoral head and of the maturation of developing bone along the superolateral acetabular roof. The acetabular angle is often increased in DDH because maturation and ossification of the acetabulum are abnormal and delayed.
- The Perkins line is drawn at the outer acetabular margin and is perpendicular to the Hilgenreiner line. These lines divide the hip into quadrants. The unossified femoral head normally is centered in the inferomedial quadrant (see Image 2).
Frontal radiograph of the pelvis obtained in an infant before ossification of the capital femoral epiphyses begins. The legs are in the neutral position. The projected location of the unossified femoral heads must be estimated. The right hip is normal. The probable location of the left femoral head projects beyond the joint space and into the lower outer quadrant formed by the intersection of the Hilgenreiner and Perkin lines.
- In the normal hip, the Shenton line is a smooth unbroken arc that bridges the medial femoral metaphysis and the inferior edge of the superior pubic ramus. Displacement of the femoral head out of the joint space and disruption of the Shenton line are suggestive of DDH.
Delayed ossification of the femoral epiphysis is observed in the unstable hip. A false acetabulum eventually develops secondary to molding of the displaced ossification center against the bony pelvis (see Image 3).
Frontal radiograph of the pelvis in a 1-year-old child with a dislocated right hip. The degree of ossification of the femoral head on the dislocated side is decreased compared with that of the normally located left hip. The abnormally located hip articulates with a false neoacetabulum.
To assess reducibility, a frontal view of the pelvis can be obtained with the legs in external rotation (ie, frog-leg position; see Image 4).
Frontal radiograph of the pelvis obtained with the legs in the frog-leg position indicates that the plane of the femoral projection is toward the triradiate cartilage, suggesting that the hips are reducible.
Degree of Confidence
Plain radiography has a low sensitivity, exposes the infant to ionizing radiation, and does not provide dynamic information. Radiographs are difficult to interpret before the capital femoral epiphyses ossify.
False Positives/Negatives
Because some hips may be subluxatable but not frankly dislocated or dislocatable only with Barlow maneuvers, plain radiographs obtained in neonates or infants with their hips in the neutral position frequently fail to depict DDH.
Computed Tomography
Findings
CT is useful for evaluating complicated dislocations and for postoperative evaluation of the hip. CT can depict osseous blocks to relocation, as well as iliopsoas tendon capsule constriction, a thick ligamentum teres, and fibrofatty pulvinar hypertrophy. CT can also be used to evaluate femoral and acetabular anteversion.20
In infants with spica casts, low-milliamperage selective thin-section CT sections can confidently and quickly assess concentric reduction before the patient is discharged.
Magnetic Resonance Imaging
Findings
MRI can be useful in the preoperative and postoperative evaluation of a hip with many complications. MRI can be used to distinguish the labrum, capsule, and acetabular cartilage. MRI is useful for detecting the complications of DDH and treatment for DDH, such as avascular necrosis of the femoral head and joint effusions. MRI can also be used to demonstrate iliopsoas tendon compression, a thick ligamentum teres, and pulvinar hypertrophy.20
Ultrasonography
Schematic drawing of the coronal plane used to assess the hip at ultrasonography. The transducer is placed on the lateral aspect of the thigh.
Schematic drawing of the transverse plane of the left hip. The anteroposterior orientation depends on whether the right or left hip is being examined. The transducer is placed in the transverse orientation over the anterior upper thigh.
Calculation of the alpha and beta angles to assess acetabular maturity. A standard coronal image is used.
Real-time coronal sonogram of the hip shows calculation of the acetabular alpha angle. An angle of 60° or greater indicates acetabular maturity.
Real-time coronal sonogram of the hip with calculation of the d/D ratio. Coverage of 58% or greater is considered normal.
Real-time transverse sonogram of the right hip obtained without stress maneuvering reveals that the cartilaginous femoral head is well centered above the triradiate cartilage between the pubis and ischium. Echoes are present through the interface with the cartilage; this appearance has been likened to that of a lollipop, in which the femoral head is the "candy" and the echoes through the cartilage are the "stick." In a normally stable hip, this appearance should be maintained with stress maneuvering.
Real-time sonogram of the right hip obtained with stress maneuvering reveals that the femoral head is posteriorly displaced over the ischium.
Coronal real-time sonogram of the hip obtained with stress maneuvering reveals significant lateral motion, which is not out of the plane of the baseline. This was accompanied by posterior motion in the transverse plane.
Coronal real-time sonogram of the hip obtained with stress maneuvering reveals that the capital femoral epiphysis displaces out of the plane of the baseline. This dislocatable hip was reimaged after Ortolani maneuvering, and the dislocation was reducible.
Findings
ACR standard US examination14 of the infant hip is performed in 2 planes, the coronal (see Image 5) and transverse (see Image 6), as follows23 :
- A high-resolution linear array transducer must be used.
- The infant may be examined in the supine or lateral decubitus position, with the hip in a 90º flexed position.
- The operator uses one hand to hold the infant's knee at a right angle to the thigh. The palm of an open hand may be placed on the small of the infant's back.
- The thigh is held in the neutral position for imaging.
The unossified cartilaginous femoral head appears as a speckled ball in the acetabular fossa. Once ossification begins, it appears as a central area of increased echogenicity in the center of the cartilaginous head.
The femoral head should be centered in the joint space, with half or more of the femoral head medial to the baseline in the coronal plane. The extent of maturity of the acetabulum can also be quantified by using angular measurements (see Image 7). The ACR considers the calculation of these measurements optional. The standard coronal sectioning plane must be used at the deepest portion of the acetabulum, where the ilium appears as a straight line, perpendicular to the femoral head and parallel to the surface of the transducer.
Acetabular maturity
To quantify acetabular maturity, alpha and beta angles are determined by the application of 3 lines drawn in the standard coronal plane (see Image 8). The baseline passes through the plane of the ilium, where it connects to the osseous acetabular convexity. The inclination line passes from the lateral end of the acetabulum to the labrum, parallel to the cartilaginous roof. The roofline passes along the plane of the bony acetabular convexity.
- The alpha angle is used most commonly as a measurement of acetabular concavity, and it is calculated as the angle between the baseline and the roofline. A normal alpha angle is 60º or greater. Angles of 50-60º may be physiologically typical in the immediate neonatal period, but hips with these angles are considered immature and require clinical and US follow-up. Angles of less than 50º are always considered abnormal and require treatment.
- The beta angle is measured between the baseline and the inclination line. It indicates the acetabular cartilaginous roof coverage. An angle of less than 55º is considered normal. The smaller the angle, the less the cartilaginous coverage and the better the bony acetabular coverage of the femoral head.
- Not all dynamic hip imagers use these angles for the diagnosis and care of babies with DDH. Many use descriptive terms instead of numbers.
In a complementary method of assessing acetabular development, the distance between the medial aspect of the femoral head and the baseline (d) is compared with the maximum diameter of the femoral head (D); this d/D ratio is expressed as a percentage. This ratio represents the coverage of the femoral head by the bony acetabulum in the standard coronal plane (see Image 9). Coverage of 58% or greater is considered normal. The smaller the coverage, the greater the acetabular immaturity.
Stress maneuvering (ie, the Barlow maneuver) with the femur in 90º of flexion and maximum adduction is performed during transverse imaging to assess stability (see Images 10-11). The use of stress is optional in coronal imaging, which may be performed with the patient's leg in a flexed or neutral position. Stress is omitted if the infant is receiving treatment for DDH with a Pavlik harness. Stress maneuvering reveals instability, subluxation (see Image 12), or dislocation (see Image 13). In dislocated hips, the Ortolani maneuver should be performed to check for reducibility.
An ancillary sign of instability is asymmetry in the degree of ossification of the femoral heads.
Degree of Confidence
Some experience is helpful in assessing hip stability because some laxity is normal in the infant's first months of life. Not all sonographically abnormal hips need treatment because spontaneous normalization is common in some infants by the time they are aged 4 weeks; therefore, the decision to treat is based not only on sonographic findings but also on clinical findings. Because many unstable hips may spontaneously normalize within the first 2 weeks of a neonate's life, delaying the first US study for 2 weeks should be considered.21
False Positives/Negatives
Mild instability may be observed in healthy neonates in their first few days of life, when the typical femoral head has a laxity of 3-4 mm on average. This amount of motion should resolve spontaneously within the first months of an infant's life, after maternal hormonal influences diminish.
Inexperienced US examiners can mistake the greater trochanter cartilage for the femoral head and incorrectly diagnose developmental dysplasia of the hip (DDH).
It has been suggested that, because US is very sensitive, a plain radiograph be performed to confirm DDH in infants over the age of 4 months with abnormal static US examinations, as ossification of the capital femoral epiphyses would begin to be present, thereby limiting over-treatment. This unnecessary exposure to ionizing radiation, however, can be avoided by the performance of a dynamic US examination.21,22
More on Developmental Dysplasia of the Hip |
| Overview: Developmental Dysplasia of the Hip |
 Imaging: Developmental Dysplasia of the Hip |
| Follow-up: Developmental Dysplasia of the Hip |
| Multimedia: Developmental Dysplasia of the Hip |
| References |
| Further Reading |
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References
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Karmazyn BK, Gunderman RB, Coley BD, Blatt ER, Bulas D, Fordham L, et al. ACR Appropriateness Criteria on developmental dysplasia of the hip--child. J Am Coll Radiol. Aug 2009;6(8):551-7. [Medline].
Krych AJ, Howard JL, Trousdale RT, Cabanela ME, Berry DJ. Total hip arthroplasty with shortening subtrochanteric osteotomy in Crowe type-IV developmental dysplasia. J Bone Joint Surg Am. Sep 2009;91(9):2213-21. [Medline].
Mahan ST, Katz JN, Kim YJ. To screen or not to screen? A decision analysis of the utility of screening for developmental dysplasia of the hip. J Bone Joint Surg Am. Jul 2009;91(7):1705-19. [Medline].
Graf R. Guide to Sonography of the Infant Hip. New York, NY: Thieme Medical; 1987.
McMillan JA, DeAngelis CD, Warshaw JB, et al, eds. Oski's Pediatrics: Principles and Practice. 3rd ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 1999.
Koureas G, Wicart P, Seringe R. Etiology of developmental hip dysplasia or dislocation: review article. Hip Int. 2007;17 Suppl 5:1-7. [Medline].
Gerscovich EO. Infant hip in developmental dysplasia: facts to consider for a successful diagnostic ultrasound examination. Appl Radiol. 1999;Mar:18-25.
Nelson WE, Behrman RE, Kliegman RM, et al. Nelson Textbook of Pediatrics. 15th ed. Philadelphia, Pa: WB Saunders; 1996.
Schwend RM, Schoenecker P, Richards BS, Flynn JM, Vitale M. Screening the newborn for developmental dysplasia of the hip: now what do we do?. J Pediatr Orthop. Sep 2007;27(6):607-10. [Medline].
Hennrikus WL. Developmental dysplasia of the hip: diagnosis and treatment in children younger than 6 months. Pediatr Ann. Dec 1999;28(12):740-6. [Medline].
Fujii M, Nakashima Y, Jingushi S, Yamamoto T, Noguchi Y, Suenaga E, et al. Intraarticular findings in symptomatic developmental dysplasia of the hip. J Pediatr Orthop. Jan-Feb 2009;29(1):9-13. [Medline].
American College of Radiology. ACR Standards, 1999-2000: American College of Radiology Standard for the Performance of the Ultrasound Examination for Detection of Developmental Dysplasia of the Hip. American College of Radiology. Available at http://www.acr.org/cgi-bin/fr?tmpl:standards00,pdf:pdf/hip_dysplasia.pdf. Accessed March 5, 2001.
Graf R. [The use of ultrasonography in developmental dysplasia of the hip.]. Acta Orthop Traumatol Turc. 2007;41 Suppl 1:6-13. [Medline].
Peled E, Eidelman M, Katzman A, Bialik V. Neonatal incidence of hip dysplasia: ten years of experience. Clin Orthop Relat Res. Apr 2008;466(4):771-5. [Medline].
Morin C, Harcke HT, MacEwen GD. The infant hip: real-time US assessment of acetabular development. Radiology. Dec 1985;157(3):673-7. [Medline].
Dezateux C, Rosendahl K. Developmental dysplasia of the hip. Lancet. May 5 2007;369(9572):1541-52. [Medline].
Kirks DR, Griscom NT. Practical Pediatric Imaging Diagnostic Radiology of Infants and Children. Philadelphia, Pa: Lippincott-Raven; 1998.
Ozonoff MB. Pediatric Orthopedic Radiology. 2nd ed. Philadelphia, Pa: WB Saunders; 1992.
Wientroub S, Grill F. Ultrasonography in developmental dysplasia of the hip. J Bone Joint Surg Am. Jul 2000;82-A(7):1004-18. [Medline].
Tudor A, Sestan B, Rakovac I, Luke-Vrbanic TS, Prpic T, Rubinic D, et al. The rational strategies for detecting developmental dysplasia of the hip at the age of 4-6 months old infants: a prospective study. Coll Antropol. Jun 2007;31(2):475-81. [Medline].
AIUM practice guideline for the performance of an ultrasound examination for detection and assessment of developmental dysplasia of the hip. J Ultrasound Med. Jan 2009;28(1):114-9. [Medline].
Kotnis R, Spiteri V, Little C, Theologis T, Wainwright A, Benson MK. Hip arthrography in the assessment of children with developmental dysplasia of the hip and Perthes' disease. J Pediatr Orthop B. May 2008;17(3):114-119. [Medline].
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Further Reading
Related eMedicine topics
Developmental Dysplasia of the Hip (Orthopedic Surgery)
Fracture, Hip (Emergency Medicine)
Dislocation, Hip (Emergency Medicine)
Hip Dislocation (Sports Medicine)
Hip Fracture (Sports Medicine)
Clinical guidelines
Screening for developmental dysplasia of the hip: recommendation statement. United States Preventive Services Task Force - Independent Expert Panel. 2006. 10 pages. NGC:004705
ACR Appropriateness Criteria® developmental dysplasia of the hip - child. American College of Radiology - Medical Specialty Society. 1999 (revised 2007). 7 pages. NGC:007008
Clinical studies
Treatment for Mild Hip Dysplasia in Newborns
Keywords
developmental dysplasia of the hip, DDH, congenital dislocation of the hips, CDH, acetabulum, femoral head, proximal femur, acetabular disorder, myelodysplasia, arthrogryposis
