The term “hip” often refers to a general region of the body, but medically, the “hip joint” is the ball-and-socket connection between the femur and the pelvis. The larger bony structure people touch when they “put their hands on their hips” is the pelvic girdle, or hip bone. The iliac crest is a prominent feature of this larger structure.
The Crest’s Place in the Pelvic Girdle
The iliac crest is the superior, curved border of the ilium. The ilium is the largest of the three bones (along with the ischium and the pubis) that fuse in adulthood to form the os coxa, or hip bone. The two hip bones and the sacrum form the ring-like pelvic girdle.
This bony ridge is a thick, flared section of the ilium designed to bear the weight of the spine and upper body. It forms a dividing line, separating the abdominal cavity above from the true pelvic cavity below.
Finding the Iliac Crest on Your Body
The iliac crest is easily found near the waistline, lying close to the skin’s surface. To locate it, a person can press down on the sides of their waist until they feel the prominent, curved, bony ridge, which is the highest part of the ilium. The crest’s highest point typically aligns horizontally with the fourth lumbar vertebra (L4), making it a reliable anatomical landmark.
Following the curve forward, the crest terminates at the anterior superior iliac spine (ASIS). The posterior end terminates at the posterior superior iliac spine (PSIS), which is also palpable.
Structural Role in Movement and Stability
The extensive, curved surface of the iliac crest acts as a broad attachment site for numerous muscles and connective tissues. This anchoring point is important for maintaining upright posture and facilitating movement of the trunk and lower limbs. The outer and inner surfaces of the crest are structured with various lips and zones to accommodate different muscle groups.
Muscles that stabilize the core and move the trunk, such as the internal and external abdominal obliques and the transversus abdominis, originate along the anterior portion of the crest. Farther back, the latissimus dorsi and portions of the gluteal muscles also attach to the crest, contributing to stability and hip extension. This concentration of muscle attachments helps the crest distribute forces efficiently, supporting the body’s weight and providing leverage for rotation and flexion.
Common Medical Uses
The iliac crest’s accessibility and internal structure make it important in clinical medicine. It contains a rich supply of red bone marrow, the site of blood cell production. Therefore, the crest is the most common location for a bone marrow aspiration or biopsy to diagnose blood disorders.
It is also used as a donor site for obtaining bone graft material, known as an iliac crest bone graft (ICBG). The harvested bone is abundant and contains osteogenic cells, which promote new bone growth when transplanted to another site. The crest is also a reliable anatomical landmark for clinicians, helping them pinpoint the location of structures like the L4 vertebral body for procedures such as lumbar punctures.