Where Is the Iliac Artery and What Is Its Function?

The iliac arteries are the two large blood vessels that form when your abdominal aorta splits near the base of your spine, roughly at the level of your belly button or slightly below. Their primary function is delivering oxygen-rich blood from the heart to everything below the waist: your pelvis, hips, reproductive organs, bladder, buttocks, and legs. Because they are the sole arterial highway to the lower body, problems in these vessels can produce symptoms ranging from leg pain during walking to life-threatening hemorrhage after trauma.

Where Exactly the Split Happens

Your aorta, the body’s largest artery, runs down from the heart through the chest and abdomen. At its lowest point, it divides into a right and left common iliac artery. A meta-analysis pooling data from nearly 5,800 cases found that this split most commonly occurs at the level of the fourth lumbar vertebra, in about 60% of people.¹ That vertebra sits roughly behind your navel, a few inches above the rim of the pelvis. In some people the split happens a vertebra higher or lower, which matters to surgeons planning procedures but doesn’t change anything you’d feel day to day.

Each common iliac artery is only a few centimeters long before it divides again into two branches: the external iliac artery and the internal iliac artery. That second fork typically happens near the sacroiliac joint, where the base of your spine meets the pelvis. From there, the two branches head in distinctly different directions and serve very different territories.

External Versus Internal Iliac Arteries

The external iliac artery continues downward and forward, running along the inner edge of the pelvis until it ducks under the inguinal ligament in your groin. Once it crosses that ligament, its name changes to the femoral artery, and it becomes the main blood supply to your entire leg. If you’ve ever had your pulse checked at the groin crease, the pulse you felt was the femoral artery, which is really just the continuation of the external iliac.

The internal iliac artery, by contrast, dives deeper into the pelvis. It feeds the pelvic organs: the bladder, rectum, uterus and vagina in women, prostate and seminal vesicles in men, and the muscles of the pelvic floor, buttocks, and inner thigh. It also supplies the walls of the pelvis itself and parts of the lower spinal cord. Because its branches reach so many structures, surgeons treat it with particular caution during pelvic operations.

The internal iliac artery’s branching pattern is famously variable. A cadaveric study of 80 pelvic halves found that the branching deviated from the textbook pattern in about 61% of cases, with variations more common in the front-facing (anterior) branches than the rear-facing (posterior) ones.² In roughly 3% of cases, the internal iliac didn’t split into two divisions at all. These variations are rarely a problem in daily life, but they become critical during surgery or embolization procedures when a surgeon needs to know exactly which vessel goes where.

What Happens When the Iliac Arteries Narrow or Block

The iliac arteries are muscular, elastic tubes, and like arteries everywhere, they can develop atherosclerosis: a gradual buildup of fatty deposits that stiffens and narrows the vessel wall. When this happens in the iliac arteries, it falls under the broader umbrella of peripheral artery disease. Early on, you might notice leg pain or cramping during exercise that goes away with rest, a symptom called claudication. As narrowing worsens, pain can occur even at rest, and wounds on the feet may heal slowly.

A particularly dramatic form of iliac artery blockage is called Leriche syndrome, where the aorta and both common iliac arteries become severely occluded or completely blocked. The classic triad includes weak or absent pulses in both legs, claudication in the buttocks and thighs, and erectile dysfunction in men.³ It tends to develop gradually, often over years, which means collateral vessels sometimes have time to grow and partially compensate. Even so, the condition carries serious risks: reported mortality around 4.5–5% and complication rates around 18–20% when it comes to treatment.

Treating Iliac Artery Blockages

When blood flow through the iliac arteries is critically reduced, doctors have two broad options: pushing the blockage open from the inside using a stent, or rerouting blood around the blockage with a surgical bypass graft. Both work, but their strengths differ. A study comparing stenting to bypass surgery in patients with moderate-to-severe iliac artery disease found that bypass grafts stayed open longer: about 97% were still patent at two years, compared with roughly 80% for stents.⁴ Complication rates were similar between the two approaches, and there were no perioperative deaths in either group.

In practice, stenting is often the first choice for older patients or those with other serious health conditions, because it’s less invasive and recovery is faster. Bypass surgery tends to be reserved for younger, healthier patients where the longer-lasting result justifies a bigger operation. When heavy calcification in the artery walls makes standard CT scans hard to read, subtraction CT angiography can help clarify how severe the narrowing really is, allowing better treatment planning.⁵

Iliac Artery Aneurysms

While narrowing is the more common problem, the iliac arteries can also bulge outward, forming an aneurysm. Isolated iliac artery aneurysms are uncommon, and they tend to be clinically silent, producing no symptoms until they grow large enough to cause trouble.⁶ Autopsy studies have linked rupture to extensive bleeding behind the abdominal organs (retroperitoneal hemorrhage), and histological examination of ruptured aneurysms typically shows atherosclerotic changes and inflammation in the arterial wall.

A study tracking 189 patients with iliac artery aneurysms found that the growth rate was slow for aneurysms smaller than 3 cm, averaging about 1 mm per year. Aneurysms between 3 and 5 cm expanded more than twice as fast. All patients who developed symptoms or needed surgery had aneurysms larger than 4 cm.⁷ That 4 cm threshold has become a practical guide for when to consider intervention versus continued monitoring.

The Iliac Arteries in Pelvic Trauma

Pelvic fractures rank among the most dangerous injuries in multi-system trauma, second only to head injuries as a cause of death in patients with multiple broken bones.⁸ The primary killer in these cases is uncontrolled bleeding, and the iliac arteries are particularly vulnerable because of where they sit. They run along the inner pelvic wall, tethered by ligaments and fascia, which means a fracture can damage them in several ways: a bone fragment can pierce the vessel directly, shearing forces can tear the inner lining, or compression between fracture fragments can crush the artery closed.⁹

Even partial damage to the arterial lining can be dangerous: platelets pile up at the injured spot and can form a clot that blocks the vessel, cutting off blood flow to the leg. Emergency treatment may involve embolization, where interventional radiologists thread a catheter to the bleeding vessel and seal it off with tiny particles or coils. While this can be lifesaving, it comes with trade-offs. One study found that patients who underwent bilateral internal iliac artery embolization had a complication rate of 20%, compared with about 5% in similar patients who didn’t need embolization.¹⁰

What Happens When the Internal Iliac Artery Is Blocked on Purpose

Sometimes surgeons deliberately block or bypass the internal iliac artery during operations for aortic aneurysms, cancer, or trauma. This raises an obvious concern: if you shut off blood to the pelvic organs, won’t things go wrong? The pelvis has a surprisingly rich network of collateral vessels that can reroute blood flow. Research on patients whose internal iliac artery was interrupted during aneurysm repair found that a key collateral pathway runs from the deep femoral artery in the thigh back up into the pelvis through the obturator artery, effectively feeding the pelvis from below.¹¹

These collateral pathways are usually enough to prevent catastrophic pelvic ischemia, but they don’t always prevent symptoms entirely. About a third of patients who had the internal iliac artery interrupted during aneurysm repair developed buttock claudication, a cramping pain in the buttocks when walking.¹² More serious complications like bowel ischemia or spinal cord problems were not observed in that study, but they remain a known risk in the literature, particularly when both internal iliacs are blocked simultaneously. Long-term follow-up of patients who underwent emergency iliac artery embolization for trauma found that buttock, thigh, and perineal numbness occurred at a higher rate than in patients who weren’t embolized.¹³

The Iliac Arteries in Kidney Transplantation

If you’ve ever seen a diagram of a transplanted kidney, you probably noticed it sits much lower than a native kidney, tucked into the pelvis rather than up against the back ribs. That’s because transplant surgeons connect the donor kidney’s artery directly to one of the iliac arteries. The external iliac artery is more commonly used because of its favorable size and position, while the internal iliac artery is used less often due to concerns about reducing blood flow to the pelvis.¹⁴

A comparison of 345 living-donor kidney transplants at one institution examined outcomes when the donor artery was connected to the external iliac versus the internal iliac artery.¹⁵ Both approaches can provide adequate perfusion to the transplant kidney, and the choice often depends on the individual anatomy: the size and quality of each iliac artery, whether prior surgery or atherosclerosis has compromised one vessel, and the specifics of the donor kidney’s arterial anatomy.

Iliac Artery Problems in Endurance Athletes

One of the more surprising conditions affecting the iliac arteries shows up in young, fit cyclists and triathletes. External iliac artery endofibrosis is a form of flow-limiting arterial disease caused by the repetitive demands of endurance sports. The mechanism involves the combination of extreme hip flexion during cycling and the very high blood flow rates these athletes sustain during exercise. Over time, the artery elongates, develops kinks, and suffers microtrauma to its inner wall, leading to a thickening of the lining that gradually narrows the vessel.¹⁶

Affected athletes typically notice a progressive drop in performance, especially at high intensity. One leg may feel weaker or heavier than the other during hard efforts. The condition can be tricky to diagnose because the artery often looks normal at rest; it’s only under the extreme flow demands of maximal exercise that the narrowing becomes significant enough to limit blood delivery to the leg. Diagnosis usually requires exercise testing combined with vascular imaging. Treatment ranges from surgery to remove the thickened tissue to, in some cases, simply reducing training intensity and avoiding the sustained hip flexion positions that provoke the problem.

How the Iliac Arteries Change with Age

Like all arteries, the iliacs stiffen and remodel over a lifetime, but they also tend to become more tortuous, meaning they develop bends and curves that weren’t there in youth. A study examining iliac artery shape in patients with and without aortic aneurysms found that age was the single demographic factor most strongly associated with increased tortuosity in both groups.¹⁷ In people without aneurysms, the correlation between age and tortuosity was particularly strong.

This matters most when doctors need to thread catheters or stent grafts through the iliac arteries to reach the aorta, a common approach for treating aortic aneurysms and performing cardiac procedures. Severely kinked or tortuous iliac arteries can make it difficult or impossible to navigate devices through, sometimes forcing surgeons to use alternative access points or to straighten the vessel with a stiff guidewire before proceeding. It’s one reason vascular imaging before these procedures pays close attention to iliac anatomy, not just the target vessel higher up.

Adaptations During Pregnancy

Pregnancy demands massive increases in blood flow to the uterus, and the iliac arteries are the pipeline that delivers it. Research using Doppler ultrasound to track blood flow patterns in the internal iliac and uterine arteries throughout pregnancy found an interesting divergence: as pregnancy progressed, resistance in the uterine arteries dropped steadily, allowing more blood through to the placenta, while resistance in the internal iliac arteries actually increased.¹⁸ This pattern held in both women with normal blood pressure and those with chronic hypertension, suggesting it reflects a built-in regulatory mechanism in the pelvic circulation rather than a response to blood pressure alone. The internal iliac artery seems to function as a kind of upstream gatekeeper, adjusting its resistance to help direct blood preferentially into the expanding uterine circulation.

A Rare Developmental Quirk That Starts in the Womb

During early embryonic development, the main blood supply to the developing leg doesn’t come from what will become the femoral artery. It comes from the internal iliac artery, via a vessel called the axial (or sciatic) artery. Normally, the femoral system takes over as the dominant supply to the leg, and the axial artery mostly disappears, leaving behind only small remnants that persist as segments of the adult gluteal and popliteal arteries.¹⁹

In rare cases, the axial artery never regresses, and the leg continues to receive its main blood supply through this primitive pathway running alongside or through the sciatic nerve, rather than through the usual femoral route. This condition, called persistent sciatic artery, is often discovered incidentally during imaging for something else, or when the patient develops a pulsatile mass in the buttock (an aneurysm of the persistent vessel). It has been reported in case series from around the world, though it remains exceptionally uncommon.²⁰ Awareness of this anomaly matters most to surgeons and radiologists, who need to recognize it to avoid accidentally ligating what turns out to be the patient’s only arterial supply to the leg.