Developmental dysplasia of the hip
Developmental dysplasia of the hip
Ultrasound
Alpha angle
The alpha angle is formed by the acetabular roof to the vertical cortex of the ilium. The normal value is greater than or equal to 60º.
Ultrasound is the test of choice in the infant (<6 months) as the proximal femoral epiphysis has not yet significantly ossified.
Radiograph
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.
SCFE / Klein line
The Klein line is drawn along the lateral aspect of the femoral neck and should intersect a portion of the lateral capital epiphysis.
On the right, the green line indicates the normal appearance of the Klein line.
On the left, the red line is abnormal and barely intersects the capital epiphysis.