Fig. 4.

The International Hip Dysplasia Institute (IHDI) criteria are a means of classifying DDH disease severity even when the ossification center is absent [22]. To start, Hilgenreiner’s line (H-line) is drawn through the top of the triradiate cartilages bilaterally. Next, Perkin’s line (P-line) is drawn at the superolateral margin of the acetabulum perpendicular to the H-line. A diagonal line is then drawn 45° inferolaterally from the junction of the H-line and P-line. Finally, based on the location of the midpoint of the superior margin of the ossified metaphysis, as shown here with a black oval, the residual deformity may be graded from 1 to 4. In this example, the patient has an IHDI grade of 1.