Ilium

The ilium is the largest part of the hip bone: the broad, flaring blade whose top edge — the iliac crest — is the 'hip' you rest your hands on. Its inner surface supports the abdominal contents, its outer surface carries the great gluteal muscles of walking, and its lower part forms the top of the hip socket.

Key facts

The ilium forms the upper two-fifths of the hip socket.
Its crest runs from the front point (ASIS) to the back point (PSIS) of the pelvis.
The gluteal muscles that stabilise walking attach to its outer surface.
Its inner hollow (iliac fossa) holds the iliacus muscle and rests against the bowel.
It is a common site for taking bone grafts and marrow samples.

What can go wrong

The iliac crest is a familiar landmark for procedures such as lumbar puncture level-finding and bone-marrow biopsy. The front point of the ilium can be strained where the thigh muscles attach in sport (a 'hip pointer' bruise). The ilium can fracture in pelvic injuries and, in adolescents, small pieces can be pulled off by sudden muscle contractions at its growth points.

Related procedures & tests

Bone marrow biopsy

Related symptoms

Hip pain

Related muscles

Frequently asked questions

What is the iliac crest used for in examinations?

Its top edge lines up roughly with the fourth lumbar vertebra, so clinicians use it to find the right level for lumbar punctures and spinal anaesthesia.

Why do sprinters tear off a bit of the ilium?

In teenagers the crest and its front point are still cartilage growth plates, weaker than the muscles attached to them. A violent sprint start or kick can avulse a small fragment.

Educational information only. This atlas explains normal anatomy and describes conditions in general terms; it is not medical advice and does not replace assessment by a qualified clinician. If you have symptoms that worry you, seek medical care.