CorpusHuman Anatomy
SkeletalBone

Ilium

Os ilium

Also known as: iliac crest, ASIS, anterior superior iliac spine, PSIS

The largest, uppermost part of the hip bone, consisting of a body (contributing to the acetabulum) and a broad wing (ala) whose upper margin is the iliac crest.

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Overview

The iliac crest runs from the anterior superior iliac spine (ASIS) to the posterior superior iliac spine (PSIS); ≈5 cm behind the ASIS its outer lip thickens into the tubercle of the iliac crest. Below the ASIS lies the anterior inferior iliac spine (AIIS), and below the PSIS the posterior inferior iliac spine, beyond which the bone curves sharply as the greater sciatic notch.

The smooth, concave inner surface is the iliac fossa (origin of iliacus), bounded below by the arcuate line (part of the pelvic brim). Behind it, the rough auricular surface articulates with the sacrum and the iliac tuberosity above it anchors the interosseous sacroiliac ligaments. The outer gluteal surface is marked by the posterior, anterior and inferior gluteal lines, which separate the origins of gluteus maximus, medius and minimus.

The highest points of the iliac crests lie at the level of the L4 spinous process (supracristal plane). The PSIS lie at S2 — marked by skin dimples ("dimples of Venus"), level with the end of the dural sac.

Location

Upper part of the hip bone; palpable crest at the waist.

Parts & subdivisions

  1. Iliac crest
    Attachment of abdominal wall muscles, latissimus dorsi, quadratus lumborum, fascia lata; site of bone-marrow biopsy and bone graft harvest.
  2. Anterior superior iliac spine (ASIS)
    Origin of sartorius and tensor fasciae latae; lateral attachment of the inguinal ligament.
  3. Anterior inferior iliac spine (AIIS)
    Straight head of rectus femoris; iliofemoral ligament.
  4. Posterior superior iliac spine (PSIS)
    At S2; marked by sacral dimples.
  5. Iliac fossa
    Origin of iliacus.
  6. Arcuate line
    Part of the pelvic brim.
  7. Auricular surface
    Articulates with the sacrum.
  8. Gluteal lines
    Separate the origins of gluteus maximus, medius and minimus.

Anatomy

Articulations

Sacrum (sacroiliac joint); fused with ischium and pubis at the acetabulum.

Ossification

Primary centre above the greater sciatic notch ≈week 9; secondary centres for the iliac crest (appears ≈13–15 y, fuses ≈20–25 y — Risser sign of skeletal maturity) and AIIS.

Function

  • Forms the upper part of the acetabulum and pelvic wall
  • Transmits weight from the sacrum to the acetabulum
  • Attachment for gluteal, abdominal, back and thigh muscles
  • Red marrow site throughout life

Clinical significance

Avulsion fractures in adolescents

Sudden muscle contraction avulses the unfused apophyses: ASIS (sartorius — sprinters), AIIS (rectus femoris — kicking), ischial tuberosity (hamstrings).

Bone marrow biopsy and graft

The posterior iliac crest is the preferred site for marrow aspiration and trephine biopsy; the anterior crest is a common source of autologous bone graft.

Meralgia paraesthetica

Compression of the lateral femoral cutaneous nerve as it passes near the ASIS under the inguinal ligament — burning numbness over the lateral thigh (tight belts, obesity, pregnancy).

Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.