Epiphyseal-shaft angle of Southwick

One line is drawn between the anterior and posterior tips of the epiphysis at the level of the growth plate. A second line is drawn perpendicular to the first. A third line is drawn along the mid-axis of the femoral shaft. The epiphyseal-shaft angle is measured at the intersection of the second and third lines. It is measured for both hips. The magnitude of slip displacement is the angle of the involved hip minus the angle of the contralateral normal hip (or minus 12 degrees if the slip is bilateral).