Iliac crest

The crest of the ilium (or iliac crest) is the superior border of the wing of ilium and the superiolateral margin of the greater pelvis.
Structure.
The iliac crest stretches posteriorly from the anterior superior iliac spine (ASIS) to the posterior superior iliac spine (PSIS). Behind the ASIS, it divides into an outer and inner lip separated by the intermediate zone. The outer lip bulges laterally into the iliac tubercle.
Palpable in its entire length, the crest is convex superiorly but is sinuously curved, being concave inward in front, concave outward behind.
It is thinner at the center than at the extremities.
Development.
The iliac crest is derived from endochondral bone.
Function.
To the external lip are attached the "Tensor fasciae latae", "Obliquus externus abdominis", and "Latissimus dorsi", and along its whole length the "fascia lata"; to the intermediate line, the "Obliquus internus abdominis".
To the internal lip, the "iliac fascia", the "Transversus abdominis", Quadratus lumborum, Sacrospinalis, and "Iliacus".
Clinical significance.
The iliac crest has a large amount of red bone marrow, and thus it is the site of bone marrow harvests (from both sides) to collect the stem cells used in bone marrow transplantation. The iliac crest is also considered the most ideal donor site for bone grafting when a large quantity of bone is needed. For example, oral and maxillofacial surgeons will often use iliac crest bone to fill in large osseous defects of the oral cavity caused by severe periodontal disease, excess bone resorption following tooth loss, trauma, or congenital defects including alveolar clefts.
The top of the iliac crests also marks the level of the fourth lumbar vertebral body (L4), above or below which lumbar puncture may be performed.