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Posterior superior iliac spine

The back end of the iliac crest, lying under the small skin dimples either side of the sacrum.

Abbrev.PSIS
BoneIlium (hip bone)
RegionHip

Find it

  1. Client prone.
  2. Look for the two small dimples (the "dimples of Venus") just above the buttocks; the PSIS lies directly under each dimple.
  3. If the dimples are not visible, follow the iliac crest backwards with your thumbs until it ends in a rounded knob beside the sacrum.
  4. Rest a thumb on each PSIS to compare sides. A line joining them passes over the second sacral spinous process (S2).

The PSIS gives attachment to multifidus and to part of the posterior sacroiliac ligaments. It sits over the sacroiliac joint, so it marks where the sacrum meets the pelvis.

Erector spinae and gluteus maximus both begin in the area around it, which makes the PSIS a useful reference when working the lower back and upper buttock.

Muscles attaching or palpated here

  • Erector spinae — Three long columns of muscle (iliocostalis, longissimus and spinalis) running beside the spine from the sacrum to the skull that extend and side-bend the back and hold the trunk upright.
  • Gluteus maximus — The largest and most superficial buttock muscle, and the main extensor of the hip.
  • Gluteus medius — Thick, fan-shaped muscle on the outer side of the pelvis that abducts the hip and keeps the pelvis level when you stand on one leg.
  • Multifidus — Series of short, deep muscle bundles filling the groove beside the spinous processes from the sacrum to C2 that extend and steady each segment of the spine.
  • Piriformis — Flat, pear-shaped deep hip muscle running from the front of the sacrum to the greater trochanter that laterally rotates the hip.

Sources

  1. Wikipedia: Posterior superior iliac spine
  2. Wikipedia: Dimples of Venus
  3. Gray's Anatomy (1918), The Hip Bone (Bartleby, archived)