Posterior Inferior Iliac Spine Of The Hip Shown, Medial View

Description

Posterior inferior iliac spine (PIIS) sits on the posterior border of the ilium, immediately inferior to the posterior superior iliac spine and at the caudal end of the auricular surface that articulates with the sacrum at the sacroiliac joint. From a medial perspective, the PIIS is seen as a discrete bony projection bordering the posterior margin of the iliac tuberosity and lying superior to the greater sciatic notch, with the auricular surface positioned anteromedially and the roughened ligamentous area positioned posteromedially. Relationships are tight here. The landmark reads as a transition point between the smooth articular region and the rugged attachment surface. Clinically, the PIIS marks the inferior extent of the posterior sacroiliac region where the posterior sacroiliac ligaments span from ilium to sacrum, a common generator of pain in suspected sacroiliac joint dysfunction and a frequent reference point when correlating tenderness with joint line anatomy. A medial view helps separate the auricular surface from the adjacent nonarticular iliac tuberosity, which is often conflated in teaching and can complicate interpretation of erosions, sclerosis, or irregularity on CT or MRI in inflammatory sacroiliitis. It also supports surgical and interventional planning by clarifying where the posterior ilium thickens near the notch, a consideration for safe bony corridors and avoiding inadvertent violation of the sacroiliac joint. Use this illustration in pelvic osteology labs to teach the boundaries of the auricular surface, in radiology or rheumatology texts discussing sacroiliitis, and in pain medicine materials that map posterior pelvic landmarks to fluoroscopic or CT-guided sacroiliac joint injection approaches. Anatomical accuracy verified by SciePro's Medical Advisory Board.