The pelvis connects the trunk to the lower limbs. The largest of the three fused hip bones within the pelvis is the ilium, which flares outward to form the bony prominence commonly felt at the hip. The iliac crest is the superior, curved border of this flared ilium, acting as a significant anatomical landmark. This ridge is easily accessible just beneath the skin, giving it importance for daily movements and various medical procedures.
Defining the Iliac Crest
The iliac crest is the long, curved upper edge of the ilium. It extends from the front of the hip around the side to the back, forming the superolateral margin of the greater pelvis. This firm, bony ridge is easily felt just below the waistline when placing hands on the hips. Its location marks the boundary between the abdomen above and the pelvic cavity below.
The crest’s highest point is typically situated slightly behind its midpoint, aligning with the fourth lumbar vertebra (L4). The line connecting the tops of the two iliac crests, known as the intercristal line, is used as a consistent anatomical reference point. The crest is convex, curving outward along its top edge, and is sinuously curved, being slightly concave toward the body’s center in the front and convex toward the back.
Structural Components and Key Landmarks
The iliac crest is a substantial bony border, thicker at its ends and thinner toward its center. The crest’s anterior portion is a broad surface divided into three distinct sections: the outer lip, the intermediate zone, and the inner lip. These sections provide separate attachment sites for numerous muscles and connective tissues that contribute to core stability and movement.
The crest is terminated by two prominent bony projections. At the front, the Anterior Superior Iliac Spine (ASIS) is a pointed process easily felt beneath the skin. At the posterior end, the crest terminates at the Posterior Superior Iliac Spine (PSIS), often marked by small dimples in the lower back. Slightly behind the ASIS is the Iliac Tubercle, an outward bulge that serves as an attachment point for the iliotibial tract.
Essential Roles in Movement and Support
The primary function of the iliac crest is to serve as a major anchor point for a complex network of muscles and ligaments. It provides a broad surface for the attachment of several core and abdominal muscles, including the external oblique, internal oblique, and transversus abdominis. These attachments are fundamental for trunk rotation, lateral flexion, and maintaining the intra-abdominal pressure necessary for core stability.
The crest is also the origin point for large muscles of the back, such as the latissimus dorsi and erector spinae group, and hip muscles like the gluteus maximus and tensor fasciae latae. This multitude of muscular connections makes the iliac crest indispensable for locomotion, allowing for efficient hip movement, standing, and walking. The crest also plays a significant biomechanical role by distributing the weight of the upper body through the pelvis to the lower limbs, maintaining structural integrity and balance.
Medical Significance
Due to its accessible location and unique internal structure, the iliac crest holds considerable importance in the medical field. The crest contains a rich supply of red bone marrow, making it the most common and safest site for bone marrow aspiration or biopsy procedures. The posterior iliac crest is frequently chosen for these procedures because of its high marrow content and reduced risk of injury to adjacent structures.
The iliac crest is also a preferred source for autologous bone grafts, where a patient’s own bone tissue is harvested for use in reconstructive surgeries. The bone collected offers both structural support and osteogenic cells necessary for new bone formation. Clinicians use the crest as a reliable anatomical landmark for various diagnostic and surgical measurements, such as determining the level of the L4 vertebra for procedures like a lumbar puncture.