Developmental dysplasia of the hip
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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.
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 include 1,4:
female gender (M:F ~1:8)
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.
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.
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.
Treatment and prognosis
Management options include:
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