Median sacral artery

The median sacral artery is a small, unpaired artery that originates from the posterior aspect of the abdominal aorta, near its bifurcation into the common iliac arteries. It runs down the midline of the body, along the sacrum and coccyx, providing blood to these structures and surrounding tissues. Despite being relatively small, it plays a key role in vascularizing the sacral and coccygeal areas, including some muscles and vertebrae in this region.

Location

The median sacral artery arises just above the bifurcation of the abdominal aorta, typically at the level of the L4 or L5 vertebra. It descends vertically along the midline of the body, following the anterior surface of the sacrum and coccyx. As it travels, it provides small branches to the surrounding areas, including the sacrum, coccyx, and occasionally the lower lumbar vertebrae. The artery terminates near the coccyx, forming an anastomosis with the lateral sacral arteries and other smaller vessels in the region.

Anatomy

The median sacral artery is a small, midline artery that runs down the posterior part of the body, mainly supplying blood to the sacrum, coccyx, and surrounding structures. Though it is often considered a minor artery, its anatomical course and branches are important for understanding its role in vascularizing the lower back and pelvic regions.

Origin

The median sacral artery typically arises from the posterior surface of the abdominal aorta, near the point where the aorta bifurcates into the left and right common iliac arteries. This bifurcation usually occurs at the level of the fourth lumbar vertebra (L4) or fifth lumbar vertebra (L5). In some cases, the median sacral artery may originate from the point of bifurcation itself or even from one of the common iliac arteries.

Course

Once it arises from the abdominal aorta, the median sacral artery descends along the midline of the body, following the anterior surface of the sacrum. It continues downwards, passing over the sacral promontory and along the length of the sacrum and coccyx. The artery remains in close proximity to the midline, making it relatively easy to identify during anatomical dissections and imaging studies.

The artery travels through the retroperitoneal space, remaining posterior to the peritoneum but anterior to the sacrum, allowing it to reach the pelvic floor. As it continues downward, the artery eventually terminates at the level of the coccyx.

Branching Pattern

Although the median sacral artery is smaller compared to other major arteries in the pelvic region, it gives off several important branches along its course:

• Lateral Sacral Branches: These small branches travel laterally from the median sacral artery to supply the sacral vertebrae, sacroiliac joint, and surrounding muscles. They form anastomoses (connections) with the lateral sacral arteries, providing collateral circulation to the sacral region.
• Lumbar Branches: In some cases, small lumbar branches may arise from the median sacral artery to supply the lower lumbar vertebrae, particularly the fifth lumbar vertebra (L5).
• Anastomoses with Iliac and Sacral Arteries: The median sacral artery forms important anastomoses with the lateral sacral arteries, as well as branches of the common iliac and internal iliac arteries. These anastomoses help to provide additional blood flow to the pelvic and sacral regions.

Termination

The median sacral artery terminates near the tip of the coccyx. At this point, it often forms an anastomosis with the coccygeal branches of the lateral sacral arteries and other small vessels in the pelvic floor region. The terminal branches may also contribute to the vascular supply of the coccygeal plexus, a network of nerves and vessels located at the lower end of the spine.

Relationship to Surrounding Structures

• Abdominal Aorta and Common Iliac Arteries: The median sacral artery arises from the posterior aspect of the abdominal aorta, just superior to the bifurcation into the common iliac arteries. Its proximity to these major arteries is important for its role in collateral circulation.
• Sacral Vertebrae: As the artery descends along the sacrum, it remains close to the anterior surface of the sacral vertebrae. The lateral sacral branches that it gives off provide direct blood supply to the sacral vertebrae.
• Pelvic Muscles and Nerves: Along its course, the median sacral artery passes near the pelvic muscles and the sacral plexus, a network of nerves that supply the pelvic organs and lower limbs.
• Coccyx: The artery continues down to the coccyx, where it forms connections with other small arteries supplying this terminal part of the vertebral column.

Variations

There can be some variation in the anatomy of the median sacral artery:

• Number of Branches: In some individuals, the artery may give off fewer or more branches than usual, depending on anatomical differences in blood supply requirements.
• Origin Variations: While the artery typically originates from the abdominal aorta, in some cases it may arise from one of the common iliac arteries or from the bifurcation point of the aorta itself.

Function

The median sacral artery, though small and often considered a secondary vessel, plays important roles in supplying blood to several critical structures in the lower lumbar and pelvic regions. Its functions include vascularizing the sacrum, coccyx, lower lumbar vertebrae, and surrounding tissues. Below is a detailed breakdown of its functional significance.

Blood Supply to the Sacrum

One of the primary functions of the median sacral artery is to supply oxygenated blood to the sacral region, which includes the sacral vertebrae and related structures.

• Sacral Vertebrae: The artery provides blood to the sacral vertebrae through its small lateral branches. These branches deliver oxygen and nutrients to the bones of the sacrum, ensuring they remain healthy and structurally intact.
• Sacroiliac Joint: The artery also indirectly supplies the sacroiliac joints, which connect the sacrum to the pelvis. These joints play a key role in weight distribution and movement of the lower body.

Blood Supply to the Coccyx

The median sacral artery supplies the coccyx, the small terminal portion of the vertebral column. This is an essential function as the coccyx serves as a point of attachment for various muscles, tendons, and ligaments involved in functions like sitting and stabilizing the pelvis.

• Coccygeal Vertebrae: The artery provides small branches that supply blood to the coccygeal vertebrae, maintaining the health and integrity of the coccyx.
• Pelvic Floor Support: The artery’s blood supply helps support the muscles and soft tissues of the pelvic floor, which are anchored in part by the coccyx. This is particularly important for functions such as maintaining continence and supporting pelvic organs.

Contribution to Collateral Circulation

The median sacral artery forms anastomoses (vascular connections) with other arteries in the pelvic region, such as the lateral sacral arteries, internal iliac arteries, and common iliac arteries. These anastomoses provide an alternative pathway for blood flow, which is especially important in cases of compromised blood supply.

• Collateral Blood Flow: In case of obstruction or damage to other major arteries, the median sacral artery can help maintain blood flow to the lower lumbar and pelvic regions through its connections with adjacent arteries.
• Vascular Support in Surgery: The anastomoses formed by the median sacral artery are crucial during surgical interventions like aortic aneurysm repair or pelvic surgeries, where blood flow can be compromised.

Blood Supply to the Lower Lumbar Vertebrae

In some cases, the median sacral artery provides small branches to the lower lumbar vertebrae, particularly the fifth lumbar vertebra (L5). This contributes to the blood supply of the vertebral bodies and the intervertebral discs in this area.

L5 Vertebra: The lower lumbar vertebrae, particularly L5, receive additional vascular support from the median sacral artery, which is vital for maintaining vertebral health, particularly in a region prone to high mechanical stress due to weight bearing.

Support for Pelvic Muscles and Nerves

The median sacral artery also supports various muscles and nerves in the pelvic region. Its small branches nourish the muscles attached to the sacrum and coccyx, as well as the sacral nerve plexus, which supplies the lower limbs.

• Pelvic Muscles: The artery supplies blood to muscles attached to the sacrum and coccyx, including portions of the levator ani and coccygeus muscles, which are essential for pelvic floor function.
• Sacral Plexus: Through its contribution to the vascularization of the sacral plexus, the median sacral artery indirectly supports the nerves that control movement and sensation in the lower limbs and pelvic organs.

Support for Ligaments and Soft Tissues

The median sacral artery plays a key role in nourishing the ligaments and connective tissues of the lower spine and pelvis. These include:

• Anterior Sacrococcygeal Ligament: This ligament, which connects the sacrum to the coccyx, is supported by blood flow from the median sacral artery.
• Ligaments of the Pelvic Floor: The artery helps provide blood to the ligaments and soft tissues that form part of the pelvic floor, ensuring their structural integrity.

Nutrient and Oxygen Delivery

Like all arteries, the median sacral artery’s fundamental function is to deliver oxygen and nutrients to the tissues it supplies. This allows the bones, muscles, ligaments, and soft tissues in the sacral and coccygeal regions to function properly, repair after injury, and maintain overall health.

Clinical Significance

The median sacral artery, though small, holds important clinical relevance, particularly in the context of pelvic and vascular surgeries. It is often encountered during procedures involving the lower abdominal aorta, sacrum, or coccyx, and can pose risks if not carefully managed.

• Surgical Considerations: During procedures such as abdominal aortic aneurysm repair or pelvic surgeries, inadvertent injury to the median sacral artery can lead to excessive bleeding. Surgeons must be aware of its location and branching patterns to avoid complications.
• Collateral Circulation: The median sacral artery plays a role in collateral circulation, providing an alternative blood supply to the sacrum, pelvis, and lower lumbar region. In cases where major arteries, such as the iliac arteries, are compromised, the median sacral artery can help maintain adequate blood flow.
• Tumor Embolization: In certain pelvic or sacral tumors, the median sacral artery may be a target for embolization to reduce blood supply to the tumor and prevent excessive bleeding during surgery.
• Pelvic Trauma: In cases of pelvic trauma, especially fractures involving the sacrum or coccyx, the median sacral artery can be damaged, leading to hemorrhage. Proper imaging and careful management of this vessel are crucial in such situations.