Pediatric Radiology > Musculoskeletal > The Pediatric Hip > Developmental Dysplasia of the Hip


Developmental Dysplasia of the Hip

Developmental Dysplasia of the hip (DDH), also known as congenital hip dislocation, is recurrent subluxation or dislocation of the hip secondary to acetabular dysplasia, abnormal ligamentous laxity, or both. The acetabular dysplasia yields an increased acetabular angle and a shallow acetabular fossa. Early diagnosis of DDH is important because chronic dislocation of the femoral head can lead to growth deformity of the acetabular fossa.

DDH is much more prevalent in females than males (9:1). It also is predisposed to affect the left hip > right hip (approximately 70-75% of the time). DDH is seen bilaterally in 5% of patients.

Clinical findings of DDH include a shortened leg with decreased range of abduction when flexed, asymmetry of the gluteal folds, and positive "clicks" with dislocation (Barlow maneuver) and relocation (Ortolani maneuver).

Ultrasound is the study of choice at most centers when clinical suspicion of DDH is present. It allows the hip to be evaluated for both abnormal mobility and dysmorphic acetabular features. Ultrasound is not generally performed in the first two weeks of life due to physiologic ligamentous laxity likely from maternal estrogen effects. Ultrasound is also not generally performed after 6 months of age due to increasing ossification of the femoral head.

Plain film radiography has a very limited role in evaluation of DDH in children under 6 months of age due to the lack of ossification of the femoral head. In particular, radiographs are unreliable in children 6-12 months of age because of a lack of skeletal ossification. When radiography is used, AP views are most helpful as frogleg views are likely to reduce a subluxed or dislocated hip.

 

Coronal ultrasound of a normal right hip. Note how the echogenic iliac bone bisects the femoral head. The alpha angle in this study is measured to be > 60 degrees.

Coronal Ultrasound. This view mimics the anatomy seen on an AP view of the pelvis. The iliac bone forms an echogenic line on the horizontal which should bisect the femoral head. The alpha angle is formed by lines drawn through the roof of the acetabulum and the the straight portion of the iliac bone. A normal alpha angle measures > 60 degrees (55 degrees in newborns).

 

 

 

 

 
Coronal ultrasound demonstrating mild left hip dysplasia. Note the superior and lateral displacement of the femoral head. The line through the iliac bone barely transects the femoral head. The measured alpha angle is approximately 45 degrees.

Radiograhic features of DDH:

  • shallow acetabulum
  • acetabular angle greater than 30 degrees (same as alpha angle less than 60 degrees)
  • small capital femoral epiphysis
  • delayed ossification of the femoral head
  • acetabular sclerosis
  • loss of Shenton's curve
  • femoral head lateral to Perkin's line
  • femoral head superior to Hilgenreiner's line
  

AP pelvic radiograph of a 2-year-old girl with developmental dysplasia of the left hip. The femoral heads are partially ossified. There is a dysplastic left acetabulum (shallow left acetabulum), and a small left femoral epiphysis when compared to the right. The left proximal femoral metaphysis is displaced superiorly and laterally. Note the fraying of the proximal femoral metaphyses (this patient was also diagnosed with rickets).

 

 

Shenton's curve: smooth, curved line connecting medial border of femoral metaphysis with the superior border of the obturator foramen

Hilgenreiner's line: a horizontal line through the triradiate cartilage of the acetabulum

Perkin's line: a vertical line (perpendicular to Hilgenreiner's line) from the lateral margin of the ossified acetabular roof that is normally tangential to the lateral margin of the ossification center of the femoral head

Acetabular angle: angle that the acetabular line makes with Hilgenreiner's line