Ultrasonography
Ultrasonography (US) has been of substantial benefit in the assessment and treatment of children with developmental dysplasia of the hip (DDH). [3, 36, 37, 38] The benefit of screening all children with US is controversial. [39, 40] Even with US screening, children with hip dysplasia can be diagnosed late, and one concern with routine US evaluation of newborns is overdiagnosis of hip dysplasia (ie, increased false-positive results). [41]
The employment of US only in high-risk infants has not yet been shown to reduce the prevalence of late diagnosis of hip dysplasia. [42] However, most authors agree that it is an excellent tool for assessing children with suspected hip instability and a useful aid in the treatment of children with DDH, especially in monitoring reduction by closed methods. [43]
An ultrasound evaluation is typically performed either by assessing the alpha and beta angles or by performing a dynamic evaluation. [36, 38, 44] An alpha angle outlines the slope of the superior aspect of the bony acetabulum, with an angle greater than 60º considered normal. The beta angle, which is considered normal if less than 55º, depicts the cartilaginous component of the acetabulum. Many institutions now use a dynamic form of US, as heralded by Harcke. [43]
Plain Radiography
Standard radiographic views for DDH include a standing anteroposterior (AP) view of the pelvis, with the hips in neutral position, and a false profile view in which the patient is standing angled at 65º from the x-ray plate. The radiograph is then taken, profiling the anterior aspect of the acetabulum. If any evidence of hip subluxation is present, an abducted internal rotation view can help determine if the hip reduces and better determines the true neck-shaft angle of the proximal femur.
Radiographic evaluation is typically carried out as follows (see the image below). From an AP radiograph of the hips, a horizontal line (Hilgenreiner line) is drawn between each triradiate cartilage. Next, lines perpendicular to the Hilgenreiner line are drawn through the superolateral edge of the acetabulum (Perkin lines), dividing the hip into four quadrants. The proximal medial femur should be in the lower medial quadrant, or the ossific nucleus of the femoral head, if present (usually observed in patients aged 4-7 months), should be in the lower medial quadrant.
Typical radiographic evaluation of developmental dysplasia of hip (DDH). From anteroposterior radiograph of hips, horizontal line (Hilgenreiner line) is drawn between each triradiate cartilage. Next, lines are drawn perpendicular to Hilgenreiner line through superolateral edge of acetabulum (Perkin line), dividing hip into 4 quadrants. Proximal medial femur should be in lower medial quadrant, or ossific nucleus of femoral head, if present (usually observed in patients aged 4-7 months), should be in lower medial quadrant. Acetabular index is angle between Hilgenreiner line and line drawn from triradiate cartilage to lateral edge of acetabulum. Typically, this angle decreases with age and should measure less than 20° by 2 years of age. Shenton line is drawn from medial aspect of femoral neck to inferior border of pubic rami. It should create smooth arc that is not disrupted. Disruption of Shenton line indicates presence of some degree of hip subluxation.
Additionally, the acetabular indices can be measured. These refer to the angle between the Hilgenreiner line and a line drawn from the triradiate cartilage to the lateral edge of the acetabulum. Typically, the angle decreases with age and should measure less than 20º by the time the child is aged 2 years. [45, 46]
The Shenton line—a line drawn from the medial aspect of the femoral neck to the inferior boarder of the pubic rami—can also be evaluated. This line should create a smooth arc that is not disrupted. Disruption of the Shenton line indicates the presence of some degree of hip subluxation.
CT and MRI
Computed tomography (CT) can also be helpful in determining femoral anteversion and in determining the extent of posterior acetabular coverage. Three-dimensional (3D) images are also quite popular and can be beneficial in visualizing the overall shape of the acetabulum.
Magnetic resonance imaging (MRI) can be beneficial in identifying the underlying bony and soft-tissue anatomy. One study evaluated MRI findings in pediatric orthopedic patients who showed residual subluxation after reduction of DDH. [47] Twenty-two subjects were followed conservatively, and 14 subjects underwent corrective surgery.
The subjects in the surgery arm of the study showed the presence of a high-signal intensity area (HSIA) within the weight-bearing portion of the acetabular cartilage preoperatively, which decreased or disappeared after the surgical procedure. [47] In the conservative arm, those with HSIAs demonstrated poor acetabular growth and those without HISAs showed acetabular growth. The researchers concluded that HSIAs on MRI may be a marker for poor acetabular growth, which would make these areas valuable findings in corrective surgery decision-making.
A retrospective review compared CT with MRI in the evaluation of hip reduction in patients younger than 13 months with hip dysplasia. [48] The results indicated that whereas MRI was a viable alternative to CT, CT required significantly less scan time than MRI did and cost less. However, CT was slightly less specific than MRI was. [48]
Arthrography
Arthrography is a dynamic study, performed by injecting radiopaque dye into the hip joint and then carrying out a fluoroscopic examination, usually with the patient under anesthesia. Although it can be performed independently, it is routinely performed in conjunction with a closed reduction. Arthrography can be helpful in determining the underlying cartilaginous profile and dynamic stability of the hip. [37] It has also been used in conjunction with a hip MRI study to facilitate demonstration of labral tears.
When arthrography is performed in combination with a closed reduction, the adequacy of the reduction can be assessed. Increased medial joint space, as demonstrated by medial pooling of the dye and a rounded or interposing limbus, may be indicative of poor long-term results. After closed reduction and immobilization in a hip spica cast, a limited CT scan in the transverse plane is obtained to ensure the hip is not subluxated or dislocated posteriorly.
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Galeazzi sign is classic identifier of unilateral hip dislocation. Patient lies supine, with hips and knees flexed. Examination should demonstrate that one leg appears shorter than other. Although this appearance is usually due to hip dislocation, it is important to realize that any limb-length discrepancy results in positive Galeazzi sign.
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Typical radiographic evaluation of developmental dysplasia of hip (DDH). From anteroposterior radiograph of hips, horizontal line (Hilgenreiner line) is drawn between each triradiate cartilage. Next, lines are drawn perpendicular to Hilgenreiner line through superolateral edge of acetabulum (Perkin line), dividing hip into 4 quadrants. Proximal medial femur should be in lower medial quadrant, or ossific nucleus of femoral head, if present (usually observed in patients aged 4-7 months), should be in lower medial quadrant. Acetabular index is angle between Hilgenreiner line and line drawn from triradiate cartilage to lateral edge of acetabulum. Typically, this angle decreases with age and should measure less than 20° by 2 years of age. Shenton line is drawn from medial aspect of femoral neck to inferior border of pubic rami. It should create smooth arc that is not disrupted. Disruption of Shenton line indicates presence of some degree of hip subluxation.
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Radiographs from 6-year-old child who underwent open reduction with capsular plication, femoral shortening, and pelvic (Pemberton) osteotomy.
