Ilium (bone) — structure, function, and clinical relevance

Anatomy and parts

Structurally the ilium consists of a wing-like blade (the ala) and a lower body that contributes to the pelvis and the acetabulum, the socket for the femur. Surface landmarks include the iliac crest, iliac fossa, anterior and posterior superior and inferior iliac spines, and the auricular surface that articulates with the sacrum.

Functions and attachments

The ilium serves several mechanical and biological roles: it forms part of the pelvic ring that supports body weight, provides the acetabular margin of the hip joint, and offers broad attachment sites for major muscles such as the gluteals and iliacus. These muscle attachments are important for posture, walking and hip stability.

Evolutionary and comparative notes

Across tetrapods the shape and orientation of the ilium vary with posture and locomotion. In bipedal humans the blade is shorter and more bowl-shaped to support upright posture and reorient muscle leverage; in many quadrupeds it is elongated to match their gait mechanics.

Clinical relevance

Clinically the iliac crest is a frequent donor site for autologous bone grafts and a surface landmark for procedures such as lumbar puncture level estimation and bone marrow biopsy. Iliac fractures, osteitis, and degenerative changes at the sacroiliac joint are common conditions that involve the ilium.

Distinctions and notable facts

Do not confuse the ilium (bone) with the ileum, a portion of the small intestine; the two words are similar but refer to different body systems. The ilium should also be distinguished from the neighboring ischium and pubis, which together complete the hip bone.

• Key landmarks: iliac crest, anterior superior iliac spine, auricular surface.
• Common uses: bone graft harvest, anatomical landmarking.