Final answer:
A posterior pelvic tilt results in nutation of the sacrum, and is influenced by the stability and movement provided by the pelvic ligaments.
Step-by-step explanation:
A posterior pelvic tilt involves the rotation of the pelvis where the front rises and the back lowers, resulting in a decrease of the natural lumbar curvature.
This action creates nutation of the sacrum, which is a movement where the top of the sacrum moves anteriorly, causing the tailbone to tuck under.
Various structures including the ligaments of the pelvis such as the posterior sacroiliac ligament, which supports the sacroiliac joint, the sacrospinous ligament spanning the sacrum to the ischial spine, and the sacrotuberous ligament connecting the sacrum to the ischial tuberosity, all play a role in the stability and movement of the sacrum and pelvis.