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Ilium
Ilium is the broad, superior hip bone that articulates with the sacrum at the sacroiliac joint.
RegionPelvis and Perineum
SystemMusculoskeletal System
The ilium is the broad, flaring portion of the hip bone and is the largest of the three bones that form the os coxae, alongside the ischium and pubis. It forms the superior part of the acetabulum and serves as a major attachment site for muscles of the trunk, abdomen, and lower limb. With its wide surface area and strategic articulations, the ilium plays a critical role in transmitting weight, enabling motion, and stabilizing the pelvis during locomotion.
Structure
The ilium can be divided anatomically into two main parts: the body and the ala (wing).
Body of Ilium
- Forms the upper part of the acetabulum
- Joins the ischium and pubis in the acetabular region
- Contributes to the socket that articulates with the head of the femur
Ala (Wing) of Ilium
- The thin, expanded superior portion of the ilium
- Contains the iliac fossa on its medial surface — a concave area for iliacus muscle attachment
Key Bony Landmarks
| Landmark | Description |
|---|---|
| Iliac Crest | The curved superior border; palpable and used as a landmark in procedures like lumbar puncture |
| Anterior Superior Iliac Spine (ASIS) | Prominent projection at the anterior end of the iliac crest; origin for sartorius muscle |
| Anterior Inferior Iliac Spine (AIIS) | Located just below the ASIS; origin for rectus femoris muscle |
| Posterior Superior Iliac Spine (PSIS) | Posterior extension of the iliac crest; forms visible dimples in the lower back |
| Greater Sciatic Notch | Deep indentation below the posterior inferior iliac spine; becomes the greater sciatic foramen with ligaments |
Location
The ilium is located in the superolateral aspect of the pelvis. It extends from the acetabulum inferiorly to the iliac crest superiorly. Anteriorly, it contributes to the anterior abdominal wall through the ASIS, while posteriorly it forms part of the sacroiliac joint with the sacrum.
Function
- Weight Transfer: Transmits weight from the axial skeleton to the lower limbs through the hip joint
- Muscle Attachment: Serves as a major site of origin and insertion for abdominal, gluteal, and lower limb muscles
- Pelvic Support: Helps form the pelvic ring, supporting pelvic organs and maintaining structural integrity
- Locomotion: Assists in stabilization of the pelvis during walking, running, and standing on one leg
Muscle Attachments
| Muscle | Attachment Site on Ilium |
|---|---|
| Iliacus | Iliac fossa (medial surface of ala) |
| Gluteus Maximus | Posterior part of the iliac crest and gluteal surface |
| Gluteus Medius | Gluteal surface between anterior and posterior gluteal lines |
| Gluteus Minimus | Gluteal surface between anterior and inferior gluteal lines |
| Sartorius | Anterior superior iliac spine (ASIS) |
| Tensor Fasciae Latae | Anterior part of iliac crest |
| Rectus Femoris | Anterior inferior iliac spine (AIIS) |
| Latissimus Dorsi | Posterior iliac crest (via thoracolumbar fascia) |
Clinical Significance
- Iliac Crest Harvesting: The iliac crest is commonly used as a donor site for bone grafts in orthopedic surgery due to its accessibility and large volume of cancellous bone
- Pelvic Fractures: Iliac wing fractures can occur from blunt trauma and may be isolated or part of complex pelvic ring injuries
- ASIS Avulsion Fractures: Often seen in adolescent athletes, caused by sudden, forceful muscle contraction at the sartorius origin
- Landmark for Injections: The iliac crest is used to identify safe zones for intramuscular injections (e.g., dorsogluteal and ventrogluteal sites)
- Palpation in Clinical Exams: The ASIS and iliac crest are important for assessing pelvic alignment, leg length discrepancies, and spinal curvature
Published on May 9, 2025
Last updated on May 9, 2025
Last updated on May 9, 2025