The iliac crest is a prominent bony landmark on the human pelvis. It represents the superior border of the ilium, the largest and uppermost bone of the hip. This structure is readily palpable and serves as a key reference point for the body’s framework.
Precise Anatomical Position
The iliac crest forms the thickened, superior border of the ilium, a major component of the hip bone and pelvic girdle. When observed from above, this curved ridge exhibits an S-shape, with its anterior portion curving inward and its posterior part curving outward. It extends from a bony projection at the front called the anterior superior iliac spine (ASIS) to another projection at the back known as the posterior superior iliac spine (PSIS).
The iliac crest is not uniformly thick; it tends to be thinner towards its center compared to its ends. Approximately 5 cm behind the ASIS, a small outward bulge called the iliac tubercle can be found on the outer lip of the crest. The highest point of the iliac crest aligns with the level of the intervertebral disc between the third and fourth lumbar vertebrae (L3 and L4).
The iliac crest also delineates the lateral boundary between the abdominal and pelvic cavities. Morphologically, it can be divided into a ventral segment, making up the anterior two-thirds, and a dorsal segment, comprising the posterior one-third. The ventral segment further consists of an outer lip, an inner lip, and an intermediate zone, each serving as attachment points for various structures.
Its Importance
The iliac crest serves as a significant attachment site for a wide array of muscles, ligaments, and fascia, contributing to core stability, posture, and movement. Abdominal muscles, such as the external abdominal oblique, internal abdominal oblique, and transversus abdominis, originate here. Back muscles like the quadratus lumborum and erector spinae also attach to the iliac crest, supporting the spine. Thigh muscles, including the tensor fasciae latae, also originate from this bony ridge.
Beyond its role in musculoskeletal mechanics, the iliac crest holds clinical importance. It is a common site for bone marrow aspiration or biopsy procedures due to its large amount of red bone marrow. This makes it a frequent source for collecting stem cells used in bone marrow transplantation.
The iliac crest also serves as a reliable anatomical landmark for various medical procedures. A transverse line connecting the highest points of the left and right iliac crests, known as the supracristal plane, passes through the fourth lumbar vertebra (L4). This alignment is a key reference point for procedures like lumbar punctures. It is also a common donor site for bone grafts when a substantial quantity of bone is required, such as in oral and maxillofacial surgeries.
Finding the Iliac Crest
Locating the iliac crest on oneself is straightforward due to its subcutaneous nature, meaning it lies just beneath the skin. To find it, an individual can place their hands on the sides of their waist, often described as “putting your hands on your hips.” The curved bony ridge felt under the hands is the iliac crest.
Once the main ridge is identified, it can be traced forward to locate the anterior superior iliac spine (ASIS), the bony projection at the front end of the crest. Tracing the crest backward will lead to the posterior superior iliac spine (PSIS), a bony projection at its rear end. This palpation technique allows identification of this significant anatomical structure.