Measurement of global balance parameters. (A) Odontoid-hip axis (OD-HA) angle. OD-HA angle (white lines) is the angle between the vertical and the hightest point of the dens connecting the center of the femoral heads (black dotted line, center of the black circles). The OD-HA angle target value is +2° to -5°. (B) T1 pelvic angle (TPA). TPA (white dotted lines) corresponds to the angle between a line connecting the center of T1 to the center of the femoral heads (black dotted line, center of the black circles) and the line to the center of the S1 endplate (black line). The TPA target value is under 14°.