The iliac crest forms a prominent, curved ridge at the top of the pelvic bone, specifically the ilium, the largest component of the hip bone. It serves as a significant anatomical landmark, easily felt just below the waistline. This structure supports the human body’s framework, contributing to movement and stability. It also protects certain internal organs. Beyond its everyday functions, the iliac crest holds considerable importance in medical procedures and diagnostic assessments due to its accessibility and composition.
Anatomy and Location
The iliac crest is the superior border of the ilium, which is the widest and uppermost of the three bones that merge to form the pelvis. This curved ridge stretches from the anterior superior iliac spine (ASIS) at the front to the posterior superior iliac spine (PSIS) at the back. It is readily palpable along its entire length, making it a useful reference point in surface anatomy.
Structurally, the iliac crest is a thick, curved bony border that is generally convex superiorly but also sinuously curved, being concave inward anteriorly and convex outward posteriorly. Behind the ASIS, it divides into an outer lip, an inner lip, and an intermediate zone between them. A notable bony protrusion called the iliac tubercle is found on the outer lip, approximately 5 cm posterior to the ASIS. The iliac crest is typically located at the approximate level of the fourth lumbar vertebra (L4), serving as a dividing line between the abdominal and gluteal areas.
Functions
The iliac crest serves as an attachment point for numerous muscles, ligaments, and fasciae, integral for human movement and posture. Muscles originating or inserting here include the external oblique, internal oblique, and transversus abdominis muscles, which are part of the abdominal wall. Other attached muscles include the latissimus dorsi, quadratus lumborum, erector spinae, and gluteus maximus, contributing to back, hip, and thigh movements.
The tensor fasciae latae and sartorius muscles of the thigh also have origins along the anterior part of the iliac crest. This extensive network of muscle and ligament attachments allows the iliac crest to stabilize the body, bear the weight of the spine and upper body, and facilitate movements like bending, twisting, walking, and lifting. Furthermore, as part of the pelvic girdle, the iliac crest helps to protect the internal organs situated within the pelvic region.
Common Conditions and Injuries
The iliac crest is susceptible to various injuries, particularly in athletes. A common issue is an iliac crest contusion, often referred to as a “hip pointer.” This injury typically results from a direct blow or a fall directly onto the iliac crest, leading to pain, swelling, and bruising (ecchymosis) in the affected area. The impact can also cause bleeding into the surrounding hip abductor musculature, limiting hip range of motion and strength due to pain.
Another condition affecting the iliac crest, especially in adolescents, is apophysitis. This involves inflammation of the growth plate where muscles attach, and it usually develops gradually due to strenuous muscle overuse in activities like running or gymnastics. Symptoms often include dull pain that worsens with activity and local tenderness at the site of inflammation.
Avulsion fractures can also occur at the iliac crest, particularly in teenagers, where a small piece of bone separates due to a sudden, forceful contraction or pull of an attached muscle. These fractures are more common in growing bone, which is weaker than mature bone. While less frequent than avulsions at other pelvic sites, iliac crest avulsion fractures can happen during activities involving trunk twisting or powerful acceleration, such as sprinting.
Its Role in Medical Procedures
The iliac crest is frequently chosen for medical procedures due to its accessibility and anatomical characteristics. It is the most common site for bone marrow aspiration and biopsy. This procedure involves inserting a needle into the bone marrow space of the iliac crest, typically the posterior superior iliac crest, to extract bone marrow for diagnostic purposes or stem cell harvesting. The posterior site is preferred for its safety, reduced pain risk, and accessibility, though the anterior superior iliac crest can be an alternative.
The iliac crest’s rich supply of red bone marrow, which produces all blood cell types, makes it an ideal source for hematopoietic stem cells (HSCs) used in bone marrow transplants. Additionally, bone marrow from this site contains mesenchymal stem cells (MSCs) that can differentiate into various cell types, holding promise for regenerative medicine.
Beyond bone marrow procedures, the iliac crest is a common donor site for autologous bone grafts in reconstructive surgeries. This bone tissue provides structural support and contains osteogenic cells that promote new bone formation, making it valuable for repairing large bone defects, such as in jaw or tibia reconstruction. Its superficial location and ample bone material allow for relatively easy surgical access, contributing to its widespread use in these clinical applications.