The posterior superior iliac spine (PSIS) is a prominent bony projection at the posterior end of the iliac crest, visible as a dimple in the lower back. It serves as an important attachment point for deep back muscles and ligaments that connect the pelvis to the sacrum. The PSIS is a crucial anatomical landmark used to assess spinal alignment and pelvic positioning, particularly in clinical settings.
The name combines "posterior" (back) and "superior" (upper) to describe its position on the iliac bone. Like its anterior counterpart, the term "spine" comes from Latin "spina," referring to its thorn-like projection.
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