Ultrasonography is the primary imaging technique for assessing the morphology and stability of the infant hip. 

It is an important adjunct to the clinical evaluation until four to six months of age 

After four to six months of age, plain radiographs are more valuable in the evaluation for DDH. 
-When AP radiographs are obtained, the hips should be in the neutral position. 
-Radiographic lines and angles are used to assess acetabular development and hip position. 
-Plain radiographic findings consistent with DDH include:
---Lateral and superior positioning of the ossified portion of the femoral head and neck
---Increased acetabular index; normal values for the acetabular index are as follows: <35° at birth; <25° at one year; <20° at two to three years; <15° at six to seven years; <11 to 12° at 10 years; and <10° at 15 years
---Delayed appearance of the femoral ossific nucleus on the involved side or asymmetric sizes of the femoral ossific nuclei