Angle between the top of S1 and the top of L1.
Normal 20-40 º
Alignment objective LL = Pelvic incidence +/- 9º
The normal, anteriorly convex curvature of the lumbar segment of the vertebral column; lumbar lordosis is a secondary curvature of the vertebral column, acquired postnatally as the upright posture is assumed when one learns to walk.
Measurement of Spino-pelvic sagittal parameters. Lumbar lordosis (LL) measured using the Cobb angle between the superior endplate of the L1 and S1. The pelvic tilt angle (PT) defined as the angle between a straight line connecting the midpoint of the bilateral femoral head centre to the midpoint of the sacral plate and the plumb line. The pelvic incidence angle (PI) defined as the angle between the perpendicular line of the sacral plate and the line of the midpoint of the superior endplate of S1 joining with the center of the hip axis. The sacral slope (SS) is defined as the angle formed by the upper endplate of S1 and the horizontal plane
In the surgical treatment of a spinal deformity, the importance of restoring lumbar lordosis is well recognized.
Smith Petersen osteotomy (SPOs) yield approximately 10° of lordosis per level, whereas pedicle subtraction osteotomies result in as much as 30° increased lumbar lordosis. Recently, selective release of the anterior longitudinal ligament (ALL) and placement of lordotic interbody grafts using the minimally invasive lateral retroperitoneal transpsoas approach (XLIF) has been performed as an attempt to increase lumbar lordosis while avoiding the morbidity of osteotomy.