The iliac crest is a curved ridge of bone that forms the upper border of the ilium, the largest of the three bones making up the pelvic girdle. This structure functions as a major anatomical landmark, often called the “hip bone,” and is easily felt beneath the skin. As the superior margin of the pelvis, the iliac crest connects the upper body to the lower limbs. It provides the attachment point for numerous muscles and connective tissues essential for human locomotion.
Location and Structure of the Iliac Crest
The iliac crest spans the entire superior edge of the ilium. It extends from the Anterior Superior Iliac Spine (ASIS) at the front, a bony projection that serves as a key reference point for clinicians and anatomists. The crest follows a convex curve backward before terminating at the Posterior Superior Iliac Spine (PSIS).
The ridge divides into three identifiable surfaces: an outer lip, an intermediate zone, and an inner lip. Approximately five centimeters behind the ASIS, the outer lip features a slight outward bulge known as the iliac tubercle, which serves as a muscular anchor. The ability to palpate the entire length of the iliac crest makes it a reliable surface landmark for locating internal structures, such as the level of the fourth lumbar vertebra.
Role in Movement and Postural Support
The primary function of the iliac crest is to support the trunk and manage the transfer of weight between the upper body and the legs. It is constantly subjected to significant biomechanical stresses during everyday activities like standing and walking. The stability it offers is maintained by a complex network of soft tissues that originate from or insert onto its broad surface.
The crest acts as the origin point for several muscle groups required for movement and posture. These include the abdominal muscles (external oblique, internal oblique, and transversus abdominis), which are necessary for core stability and trunk rotation. The iliac crest also anchors the latissimus dorsi muscle, the erector spinae muscles responsible for spinal extension, and the gluteal muscles, which are essential for hip abduction and propulsion.
Medical Procedures Utilizing the Iliac Crest
The iliac crest is a favored site in medicine due to its accessibility and composition. It is rich in cancellous bone, which contains a high volume of red bone marrow, making it an ideal source for autologous tissue collection. Bone graft harvesting frequently utilizes the iliac crest as a donor site when a patient requires bone to repair fractures or fill defects, such as during spinal fusion or reconstructive maxillofacial surgery.
The bone material collected, called an autograft, provides a scaffold for new bone growth and contains osteogenic cells that actively promote healing. The crest is also the most common location for bone marrow aspiration and biopsy, often performed to diagnose conditions like leukemia and other blood disorders. During this procedure, a specialized needle is inserted into the posterior iliac crest, typically near the PSIS, to extract a sample of liquid marrow or a core of bone tissue. The high concentration of hematopoietic stem cells makes the iliac crest ideal for these diagnostic and therapeutic harvests.
Common Sources of Iliac Crest Pain
Pain along the iliac crest often results from trauma or overuse, particularly in physically active individuals and athletes. One common acute injury is an iliac crest contusion, widely known as a “hip pointer,” which involves bruising of the bone and surrounding soft tissues. This painful condition is caused by a direct, blunt impact to the hip, often sustained during contact sports like football or hockey, and can severely limit movement.
Another frequent source of pain is iliac apophysitis, a condition occurring predominantly in skeletally immature adolescents. Since the iliac crest is a cartilaginous growth plate (apophysis) in this age group, repetitive stress from running, jumping, or twisting can cause inflammation or irritation where the abdominal and hip muscles attach. Pain can also arise from muscle strains or tears in ligaments connecting the spine to the ilium, such as the iliolumbar ligament, causing discomfort that radiates across the lower back and hip.