Fig. 2

A radiograph was used to evaluate the pelvic incidence (*) and T1 pelvic angle (T1PA, †) of a patient with a global sagittal spinal deformity [6, 19]. T1PA is defined as the acute angle by the intersection of a line from the centre of the T1 vertebral body to the femoral heads and a line from the femoral heads to the centre of the superior sacral end plate. This interplay suggests useful information from both the sagittal vertical axis and pelvic tilt simultaneously to measure the geometry of global spinal deformity