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Imaging in Developmental Dysplasia of the Hip

Practice Essentials

Developmental dysplasia of the hip (DDH) is a spectrum of disorders affecting the proximal femur and acetabulum that leads to hip subluxation and dislocation. Early diagnosis and treatment is important because failure to diagnose DDH in neonates and young infants can result in significant morbidity.

An Austrian orthopedist, Reinhard Graf, first introduced US examination of the hip in 1980.
His technique included the calculation of numerous angles, a complicated classification system of hip subtypes, and the orientation of the B-mode images so that all hips were displayed on right coronal projections. Proponents of static scanning cite that it is fast, easy to perform, and reproducible. Widespread usage in Western Europe has reduced the incidence of undetected DDH requiring open reduction to the lowest in the world.

With the advent of real-time US in 1984, H. Theodore Harcke and associates at the DuPont Institute in Wilmington, Delaware, introduced a dynamic approach to studying the hips. Harcke is the principal drafter of the American College of Radiology (ACR) standard, and his dynamic approach is predominantly used in US examination.
 There is no conclusive evidence to prefer one method over the other. However an effective ultrasonographic method should include simple, precise, quantitative and consistent definitions for a proper examination and diagnosis.

Ultrasonography (US) is the preferred modality for evaluating the hip in infants who are 6 months or younger. US enables direct imaging of the cartilaginous portions of the hip that cannot be seen on plain radiographs. Furthermore, US enables dynamic study of the hip with stress maneuvering. Practically speaking, the examination can often be successfully performed after 6 months of age (even up to 10-12 months) depending on the degree of ossification of the capital femoral epiphysis. An attempt at US examination is suggested, to limit the neonates exposure to ionizing radiation. If unsuccessful, plain films can follow.

Plain radiographs are typically obtained in the frontal pelvis, with the legs in the neutral position. If the hips are displaced or dysplastic, a second view may be obtained, with the hips in flexion and external rotation (ie, the frog-leg position) to look for reduction. The gonads of male patients should be shielded whenever possible.
 

The capital femoral epiphyses begin to ossify when an infant is aged 2-8 months. As the size of the ossification centers enlarge, shadowing may obscure the deeper acetabulum and limit US examination. Plain radiography then becomes the preferred modality for evaluating the hip.

Dynamic US examination is operator-dependent, and it requires training and experience for confident evaluation of the infant hip. Also, because US is highly sensitive in hip imaging, minor abnormalities or normal early laxities may be revealed. This is especially true of static imaging alone. Some abnormalities detected by US may not be clinically significant, but they may be mistakenly overdiagnosed and overtreated.

(See the images below.) 

Frontal radiograph of the pelvis. The ossification

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.

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Frontal radiograph of the pelvis obtained in an in

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.

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Frontal radiograph of the pelvis in a 1-year-old c

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.

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Using expected-value decision analysis, Mahan et al, of Children’s Hospital in Boston, found that the screening strategy associated with the highest probability of having a nonarthritic hip at the age of 60 years was to screen all neonates for hip dysplasia with a physical examination and to use ultrasonography selectively for infants who are at high risk. The expected value of a favorable hip outcome was 0.9590 for the strategy of screening all neonates with physical examination and selective use of ultrasonography, 0.9586 for screening all neonates with physical examination and ultrasonography, and 0.9578 for no screening.

Intervention

Arthrography can be performed to assess the dislocated hip; often, it is performed at the time of surgical reduction, particularly if the reduction appears to be difficult to maintain. The indications for arthrography are fewer with the development of better sonography, the advent of magnetic resonance imaging (MRI), and the availability to confirm reductions in spica casts with computed tomography (CT) scanning.

The initial treatment for DDH involves the use of a brace that maintains the hip in flexion and abduction. The brace is worn until the clinical and radiologic examination findings are normal. Children older than 6 months usually are too large to tolerate a brace. Closed reduction under general anesthesia is usually attempted first. The reduction can be evaluated with MRI or an arthrogram and a postreduction CT scan.

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