posterior superior iliac spine posterior superior iliac spine the posterior border of the ala, shorter than the anterior, also presents two projections separated by a notch, the posterior superior iliac spine and the posterior inferior iliac spine. the posterior superior iliac spine serves for the attachment of the oblique portion of the posterior sacroiliac ligaments and the multifidus. posterior superior iliac spineright hip bone. external surface. (posterior superior spine labeled at center left.)surface anatomy of the back. posterior superior iliac spine lies in the marking of s2.detailsidentifierslatinspina iliaca posterior superiorta98a02.5.01.113ta21329fma49468anatomical terms of bone