Posterior superior iliac spine

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Anatomical landmark in the human pelvis

Posterior superior iliac spine

Right hip bone. External surface. (Posterior superior iliac spine visible at center left.)
Latin	Spina iliaca posterior superior
Nerve	Superior cluneal nerves
Precursor	Ilium (bone)
System	Skeletal system

The posterior superior iliac spine (PSIS) is an important anatomical landmark located in the pelvis. It is a bony projection at the posterior end of the iliac crest of the ilium (bone), one of the three bones that make up the hip bone.

Anatomy

The PSIS is situated at the back of the pelvis and can be palpated through the skin. It is located at the level of the second sacral vertebra (S2) and serves as an attachment point for the posterior sacroiliac ligament and the thoracolumbar fascia. The PSIS is also a reference point for the sacroiliac joint, which connects the sacrum to the ilium.

Function

The PSIS plays a crucial role in the stability and movement of the pelvis. It serves as an attachment site for several important ligaments and muscles, including the erector spinae and the multifidus. These muscles are essential for maintaining posture and enabling movements such as bending and twisting.

Clinical Significance

The PSIS is often used as a landmark in various medical procedures, including lumbar punctures and epidural anesthesia. It is also a key reference point in the diagnosis and treatment of sacroiliac joint dysfunction and other lower back pain conditions. Palpation of the PSIS can help healthcare providers assess the alignment and symmetry of the pelvis.

Related Structures

• Anterior superior iliac spine
• Iliac crest
• Sacroiliac joint
• Sacrum
• Hip bone

See Also

• Pelvis
• Skeletal system
• Ligament
• Muscle