Common iliac artery

The common iliac artery is a large blood vessel that arises from the bifurcation of the abdominal aorta at the level of the fourth lumbar vertebra (L4). It is the primary artery that supplies blood to the pelvis and lower limbs, eventually splitting into the internal iliac artery, which supplies the pelvic organs, and the external iliac artery, which continues into the lower limbs as the femoral artery.

Location

The common iliac artery is located in the lower abdomen and pelvis. It originates at the bifurcation of the abdominal aorta at the level of the L4 vertebra and travels downward along the lateral aspect of the vertebral column. It runs anterior to the psoas major muscle on both sides and bifurcates at the level of the sacroiliac joint into the internal and external iliac arteries.

Anatomy

The common iliac artery is a major blood vessel that plays a crucial role in delivering blood to the pelvis and lower limbs. It arises from the abdominal aorta and divides into two primary branches that further supply the pelvic organs and lower extremities. Below is a detailed description of its anatomy, including its origin, course, branches, and relations with other structures.

Origin

The common iliac artery originates from the bifurcation of the abdominal aorta at the level of the fourth lumbar vertebra (L4). This bifurcation occurs just above the pelvis and marks the transition from the abdominal aorta into the two common iliac arteries, one on each side of the body. The right and left common iliac arteries supply blood to the lower abdomen, pelvis, and lower limbs.

Course

After originating from the abdominal aorta, the common iliac artery travels inferolaterally along the posterior abdominal wall. The course of the artery can be described as follows:

• Abdominal Course: The common iliac artery descends slightly lateral from its origin, running along the anterior surface of the psoas major muscle on both sides. It is located deep within the abdomen, and as it travels, it approaches the pelvic brim.
• Pelvic Course: As the common iliac artery descends toward the pelvis, it reaches the level of the sacroiliac joint, where it bifurcates into the internal iliac artery and the external iliac artery. This bifurcation typically occurs at the level of the L5-S1 vertebral junction.

Branches

The common iliac artery divides into two main branches at the level of the sacroiliac joint:

• Internal Iliac Artery: The internal iliac artery descends into the pelvis and supplies blood to the pelvic organs, including the bladder, uterus, prostate, rectum, and parts of the gluteal region and perineum. It further divides into an anterior and posterior division, giving rise to multiple branches.
• External Iliac Artery: The external iliac artery continues along the pelvic brim toward the lower limb. It eventually passes under the inguinal ligament, becoming the femoral artery, which supplies the leg. Before this transition, the external iliac artery gives rise to the inferior epigastric artery and deep circumflex iliac artery, which supply parts of the abdominal wall.

Relations to Other Structures

The common iliac artery is situated in close proximity to several important anatomical structures as it courses through the abdomen and pelvis:

• Psoas Major Muscle: The common iliac artery runs anterior to the psoas major muscle, which is a major muscle involved in hip flexion. The artery lies close to the medial border of the muscle as it descends.
• Ureter: The ureter, which carries urine from the kidney to the bladder, crosses over the common iliac artery near its bifurcation. This anatomical relationship is important in surgical procedures involving the pelvic or abdominal regions.
• Common Iliac Vein: The common iliac vein runs posterior and slightly medial to the common iliac artery on both sides. The two veins join to form the inferior vena cava at the same level where the aorta bifurcates into the common iliac arteries.
• Lymphatic Structures: The artery is also related to several lymphatic structures, including the iliac lymph nodes, which lie along its course. These lymph nodes are important in the drainage of the pelvic organs and lower limbs.

Variations

While the common iliac artery usually follows a standard pattern, there can be anatomical variations:

• High Bifurcation: In some cases, the common iliac artery may bifurcate higher than usual, at the level of the third lumbar vertebra (L3), instead of the typical L4 level.
• Aberrant Branches: In rare cases, the common iliac artery may give rise to small aberrant branches before bifurcating into the internal and external iliac arteries. These branches may supply nearby tissues or connect with other vascular structures.

Blood Flow Division and Distribution

The bifurcation of the common iliac artery ensures that blood flow is directed toward two major regions:

• Pelvic Region (via Internal Iliac Artery): The internal iliac artery directs blood flow to the organs of the pelvis, including the bladder, rectum, reproductive organs, and parts of the musculoskeletal system such as the gluteal muscles.
• Lower Limb (via External Iliac Artery): The external iliac artery continues the flow of blood to the lower limb, becoming the femoral artery once it passes beneath the inguinal ligament. This artery supplies the muscles, bones, and skin of the leg.

Relations with Nerves

The common iliac artery has important relationships with various nerves of the lumbar plexus as it descends into the pelvis:

• Lumbosacral Trunk: The lumbosacral trunk (formed by parts of the L4 and L5 spinal nerves) runs adjacent to the common iliac artery as it crosses the pelvic brim.
• Sympathetic Chain: The sympathetic chain lies near the common iliac artery and its branches, contributing to autonomic innervation of the pelvis and lower limbs.

Function

The common iliac artery serves as a major conduit for blood flow from the abdominal aorta to the pelvis and lower limbs. It divides into two important branches that each have distinct functions in supplying oxygenated blood to various organs, tissues, and muscles. Below is a detailed explanation of its functions.

Blood Supply to the Pelvic Organs

The common iliac artery plays an indirect but vital role in supplying blood to the pelvic organs through its division into the internal iliac artery, which delivers blood to the organs and tissues within the pelvic cavity.

• Bladder and Reproductive Organs: In both males and females, the internal iliac artery (a branch of the common iliac) supplies blood to the bladder, uterus (in females), prostate (in males), vagina, and other reproductive organs. Through branches like the superior and inferior vesical arteries, the uterine artery in females, and the prostatic artery in males, the common iliac artery indirectly ensures that these organs receive the oxygen and nutrients required for normal function.
• Rectum: The internal iliac artery also provides blood to the lower portion of the rectum through the middle rectal artery, which ensures the rectal tissues remain healthy and functional.

By giving rise to the internal iliac artery, the common iliac artery ensures that the blood supply to the pelvic organs is well maintained.

Blood Supply to the Lower Limbs

The common iliac artery provides the main arterial blood supply to the lower limbs via the external iliac artery, which continues into the thigh as the femoral artery. This function is critical for leg movement, posture, and overall lower body function.

• Femoral Artery and Thigh Muscles: As the external iliac artery passes beneath the inguinal ligament, it becomes the femoral artery, which supplies the muscles of the anterior thigh, including the quadriceps. The femoral artery also sends branches to the deep tissues of the thigh via the deep femoral artery, ensuring that muscles like the hamstrings, adductors, and gluteal muscles receive adequate blood.
• Lower Leg and Foot: The femoral artery continues to supply the lower leg and foot via the popliteal artery (a continuation of the femoral artery) and its branches. Through this pathway, the common iliac artery indirectly provides oxygen and nutrients to all the tissues of the lower extremity, enabling walking, running, and other weight-bearing activities.

Blood Supply to the Abdominal Wall

The common iliac artery also supports the abdominal wall through the external iliac artery and its branches, including the inferior epigastric artery and deep circumflex iliac artery.

• Inferior Epigastric Artery: This branch supplies the rectus abdominis muscle and the anterior abdominal wall, contributing to the stability and strength of the abdominal muscles. It also plays a role in vascularizing the peritoneum and can become enlarged during the development of collateral circulation.
• Deep Circumflex Iliac Artery: This artery supplies the lateral abdominal wall and helps provide blood to the lower regions of the abdominal muscles, ensuring proper muscle function and abdominal support.

Blood Supply to the Pelvic Walls and Lumbar Muscles

The internal iliac artery, which arises from the common iliac artery, provides branches that vascularize the pelvic walls and lumbar muscles, contributing to the stability and function of the pelvic girdle and lower spine.

• Iliolumbar Artery: This artery ascends toward the iliac fossa, providing blood to the iliacus and psoas major muscles, which are essential for hip flexion and pelvic stability. It also supplies the lower lumbar vertebrae, maintaining spinal health and function.
• Lateral Sacral Arteries: These arteries supply the sacral vertebrae, sacral nerves, and spinal meninges, playing a vital role in maintaining the health of the lower spine and pelvic structures.

Role in Collateral Circulation

The common iliac artery indirectly supports collateral circulation in the pelvis, abdomen, and lower limbs by contributing to an extensive network of anastomoses (connections) between its branches and other arteries. These connections provide alternative routes for blood flow in the event of blockages or vascular injury.

• Pelvic and Lower Limb Anastomoses: The branches of the internal and external iliac arteries, such as the obturator artery, inferior epigastric artery, and femoral artery, form anastomoses with nearby vessels, ensuring consistent blood flow to the pelvis and lower limbs, even in cases of arterial disease or trauma.
• Abdominal Wall Anastomoses: The inferior epigastric artery, a branch of the external iliac artery, forms anastomoses with the superior epigastric artery (a branch of the internal thoracic artery), providing an important collateral pathway for the abdominal wall in the event of an occlusion.

Support for Hip and Pelvic Function

Through its role in supplying blood to the hip joint and pelvic muscles, the common iliac artery indirectly supports hip function and pelvic stability.

• Obturator Artery: The obturator artery, a branch of the internal iliac artery, supplies the hip joint and adductor muscles of the thigh, ensuring these structures remain functional during movement. The obturator artery also contributes to the vascularization of the acetabulum and head of the femur, playing a crucial role in joint health and mobility.
• Gluteal Arteries: The superior and inferior gluteal arteries, which are branches of the internal iliac artery, supply the gluteal muscles and help support hip extension, abduction, and rotation. These functions are essential for walking, running, and maintaining an upright posture.

Role in Reproductive and Urinary Health

By supplying blood to the pelvic organs through its branches, the common iliac artery indirectly plays a role in reproductive and urinary health.

• Reproductive Organs: In females, the internal iliac artery provides blood to the uterus, vagina, and ovaries, ensuring normal reproductive function. In males, the artery supplies the prostate and seminal vesicles, playing a role in male reproductive health.
• Urinary System: The internal iliac artery also supplies the bladder and parts of the urethra, supporting the function of the lower urinary system.

Clinical Significance

The common iliac artery is of significant clinical importance due to its role as the main vessel supplying blood to the pelvis, lower limbs, and parts of the abdominal wall. It can be involved in various vascular conditions, such as atherosclerosis, which may lead to stenosis (narrowing) or occlusion (blockage), compromising blood flow to the pelvis and legs. This can result in claudication (pain due to reduced blood flow), ischemia, or even limb-threatening conditions.

Aneurysms of the common iliac artery can also develop, particularly in elderly patients or those with cardiovascular disease, increasing the risk of rupture and life-threatening hemorrhage. Interventions like stent placement, bypass surgery, or endovascular aneurysm repair (EVAR) may be required to restore or manage blood flow.

The artery’s close relationship with the ureters, psoas major muscle, and nerves in the pelvis also makes it significant in surgical procedures like pelvic surgeries, aortic aneurysm repair, and hip surgeries, where inadvertent injury to the artery can result in severe complications, including excessive bleeding or impaired circulation to the lower limbs.