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Posterior Superior Iliac Spine

spina iliaca posterior superior

The posterior superior iliac spine is the posterior projection of the iliac crest, producing the two dimples of Venus visible on the lower back of lean individuals. It is the posterior attachment of the posterior sacroiliac ligaments and the origin of the multifidus and erector spinae at this level. The PSIS is used clinically to assess sacroiliac joint position and movement asymmetry.

Anatomical Data

Structure & Landmarks

Articulations	Sacrum via the posterior sacroiliac ligament complex
Landmarks	The dimples of Venus, visible skin dimples over the PSIS in lean individuals Landmark for sacroiliac joint assessment (innominate rotation testing) Level of S2 posteriorly
Ossification	Ossifies as part of the iliac crest apophysis, completing by the mid-twenties.

Clinical Relevance

Clinical Notes

The PSIS is the primary clinical landmark for assessing sacroiliac joint dysfunction, standing flexion test and prone knee flexion test compare PSIS movement between sides to identify asymmetric sacroiliac motion. It is also the primary bony landmark for percutaneous iliac crest bone graft harvest, where a trocar can be inserted 2 cm anterior to the PSIS to access the posterior iliac crest marrow cavity.

Palpation

With the person standing or lying face down, follow the iliac crests backward toward the sacrum with your thumbs. The crest ends in a rounded knob on each side, usually under the small skin dimples (dimples of Venus) about 4-5 cm from the midline at the level of S2. Approach from below with the thumbs pointing upward to hook under the knob.

Pathology

Common Injuries & Conditions

Sacroiliac Joint Dysfunction

Pain from the sacroiliac joint is often felt at and just below the PSIS, aggravated by standing on one leg and climbing stairs.

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