Fig. 1.

Methods for measuring pelvic flexion angle from a lateral projection radiograph of the pelvis are shown. The anterior pelvic plane (APP) angle is the angle between the line connecting the bilateral ASIS and the pubic symphysis to the vertical line (V); PA is the angle between the line connecting the posterior superior corner of S1 to the center of the femoral heads (C) to V; pelvic tilt (PT) is the angle between the line connecting the midpoint of the sacral plate to C and V; sacral slope (SS) is the angle between the superior plate of S1 and the horizontal line (H).