The International Hip Dysplasia Institute (IHDI) Classification System utilizes the Hilgenreiner and Perkins lines to create four quadrants. The lower outer quadrant is then subdivided into two regions by a 45-degree line. The center of the proximal femoral metaphysis is used as the reference point that allows for utilization of the IHDI Classification before ossification of the ossific nucleus. Grade I is considered normal. Grades II to IV indicate varying degrees of subluxation or dislocation.