Pelvic incidence (PI) is measured by identifying the center of the femoral heads on the relevant sagittal images (circles) then the midpoint between these identified on the midsagittal image to define the bicoxofemoral axis. PI is the angle then subtended by a line from the bicoxofemoral axis to the middle of the sacral endplate and a line drawn perpendicular through the center of the sacral endplate. The line from the bicoxofemoral axis to the midpoint of the sacral endplate provides the distance of the pelvic thickness (PTH) in millimeters. a)PTH=100.5 mm.