Figure 2.

Three reproducible reference planes. (A) Anterior pelvic plane (APP): both anterior superior iliac spines and pubic tubercles define a frontal plane. (B) Standardization and Terminology Committee (STC) plane: anterior superior and posterior superior iliac spines define an axial plane. (C) Sacral base plane (SB): sacral base (green) defines an axial plane; an orthogonal plane to the sacral base running through the middle of pubic tubercles defines a sagittal plane.