Table 1.

Main radiographic parameters described in the study

Parameter	Definition
Kyphosis (TK)	Angle between T12 and T4
Lordosis (LL)	Angle between S1 and L1
Pelvic incidence (PI)	Angle described by a line perpendicular to S1 endplate and one drawn from S1 endplate to the center of the femoral head
Pelvic tilt (PT)	Angle described by a line perpendicular the center of femoral head and the one drawn from S1 endplate to that point
Sacral slope (SS)	The angle between the horizontal and the sacral plate
Spinosacral angle (SSA)	The angle between the sacral plate and a line running from the center of C7 to the center of the sacral plate
Spinopelvic angle (SPA)	The angle between the line drawn from the femoral head center to sacral plate and a line running from the center of C7 to the center of the sacral plate
Spinal tilt (ST)	Angle subtended by the horizontal line and the line from the center of C7 vertebral body to the center of the upper sacral endplate
PT/PI	Ratio between pelvic tilt and pelvic incidence
SS/PI	Ratio between sacral slope and pelvic incidence
PT/SS	Ratio between pelvic tilt and sacral slope