Lumbosacral Plexus · What Is It, Nerves, and More

Published: Oct 15, 2025

Author: Anna Hernández, MD•

Editor: Alyssa Haag, MD•

Editor: Ian Mannarino, MD, MBA

Illustrator: Jillian Dunbar•

Copyeditor: Sadia Zaman, MBBS, BSc

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What is the lumbosacral plexus?

The lumbosacral plexus is a network of nerve fibers, derived from the roots of lumbar and sacral spinal nerves that branch out to form the nerves supplying the lower limb.

In the human body, there are 31 pairs of spinal nerves corresponding to a segment of the vertebral column: cervical (C1-C8), thoracic (T1-T12), lumbar (L1-L5), sacral (S1-S5), and coccygeal. In the cervical and lumbar regions, the corresponding spinal nerves unite to form the brachial and lumbosacral plexuses, from which arise the nerves of the upper and lower limbs, respectively.

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Where is the lumbosacral plexus located?

The lumbosacral plexus is formed by the anterior branches of spinal nerves L4 to L5 and S1 to S4. It is located on the posterolateral wall of the lesser pelvis, adjacent to the lumbar spine. The lumbosacral plexus then embeds itself into the psoas major muscle and later emerges in the pelvis.

What nerves are found in the lumbosacral plexus?

The lumbosacral plexus includes nerves that arise from both the lumbar plexus and sacral plexus. From superior to inferior, the major nerves that branch off the lumbar plexus include the iliohypogastric nerve, ilioinguinal nerve, genitofemoral nerve, lateral femoral cutaneous nerve, obturator nerve, and femoral nerve, as well as the lumbosacral trunk.

Ilioinguinal and Iliohypogastric Nerves
The ilioinguinal and iliohypogastric nerves arise from the L1 spinal nerve and provide motor supply to some muscles of the abdominal wall, as well as sensory inputs to the skin of the groin area.

Genitofemoral Nerve
The genitofemoral nerve arises from the L1 and L2 spinal nerves and then divides into a genital and femoral branch. In individuals assigned males at birth, the genital branch supplies the skin of the scrotum and cremaster muscle; in individuals assigned female at birth, it supplies the skin around the mons pubis and labia majora. The femoral branch of the genitofemoral nerve supplies the skin of the upper anteromedial thigh.

Lateral Femoral Cutaneous Nerve, Femoral Nerve, and Obturator Nerve
The posterior branches of L2 and L3 give rise to the lateral femoral cutaneous nerve, supplying sensation to the skin on the lateral side of the thigh. Inferior to this nerve, the posterior branches of L2 to L4 become the femoral nerve, which gives off motor branches to all the muscles of the anterior compartment of the thigh, as well as cutaneous branches that supply most of the skin of the anterior thigh. On the other hand, the anterior branches of L2 to L4 become the obturator nerve, which innervates the obturator externus and all the muscles of the medial compartment of the thigh except part of the adductor magnus and the pectineus muscle. The obturator nerve also supplies sensation to the skin on the medial side of the upper thigh.

Sciatic Nerve, Pudendal Nerve and Gluteal Nerves
Finally, the lumbosacral trunk arises from the descending part of L4 and L5 and connects the lumbar plexus with the sacral plexus.

In the lower part of the lumbosacral plexus, the first branch is the sciatic nerve, which is the largest nerve in the human body. This nerve arises from spinal nerves L4 to S3 and gives off branches that supply the hip joint, posterior muscles of the thigh, and all the muscles of the leg and foot.
Subsequently, the pudendal nerve, which arises from spinal nerves S2, S3, and S4, provides sensory inputs to the external genitalia. as well as the muscular input to perineal muscles. The superior gluteal nerve, which arises from L4, L5, and S1, and the inferior gluteal nerve, which arises from L5, S1, and S2, provide motor supply to the muscles of the gluteal region.

Other
The lumbosacral plexus also gives off five nerves that are named by the muscle they innervate. These include the quadratus femoris nerve (L4-S1), the obturator internus nerve (L5-S2), the piriformis nerve (S1-S2), and nerves to the levator ani and coccygeus, which arise from S3 and S4. Finally, the sacral plexus gives off the posterior cutaneous nerve and perforating cutaneous branches, which supply the skin of the buttocks and posteromedial thigh.

What is the clinical significance of the lumbosacral plexus?

The lumbosacral plexus can be damaged as a result of various conditions and mechanical trauma, but the most common cause of injury is spinal disc herniation. A disc herniation occurs when a tear in the outer part of the intervertebral disc allows the inside of the disc to bulge out posterior and laterally, causing compression of the local spinal nerves. When this happens, individuals might notice shooting pain down the leg, as well as numbness and muscle weakness in the areas innervated by the affected nerves.

What are the most important facts to know about the lumbosacral plexus?

The lumbosacral plexus is formed by the anterior rami of spinal nerves L4, L5, and S1 to S4, which are branches of the lumbar plexus and sacral plexus. Upon their exit from the spinal cord, these nerves divide into anterior and posterior branches which become the peripheral nerves that innervate various structures of the pelvis and lower limbs. The largest nerve in the human body, the sciatic nerve, exits the lumbosacral plexus to innervate most of the lower limb muscles.

Key Takeaways

Definition	The lumbosacral plexus is a network of nerve fibers, derived from the roots of lumbar and sacral spinal nerves that branch out to form the nerves supplying the lower limbs.
Location	- Formed by anterior branches of spinal nerves L4 to L5 and S1 to S4 - Located on posterolateral wall of the lesser pelvis, adjacent to lumbar spine - Embedded into psoas major muscle, then emerges in the pelvis
Included Nerves	- Ilioinguinal nerve - Iliohypogastric nerve - Genitofemoral nerve - Lateral femoral cutaneous nerve - Femoral nerve - Obturator nerve - Sciatic nerve - Pudendal nerve - Gluteal nerves - Quadratus femoris nerve - Obturator internus nerve - Piriformis nerve - Nerves to the levator ani and coccygeus - Posterior cutaneous nerve
Clinical Significance	- Spinal disc herniation - Most common cause of injury - Disc bulges out posterior and laterally - Local spinal nerves are compressed - Causes shooting pain down the leg, numbness, muscle weakness

References

Amudha G, Diwan S. Anatomy of lumbar plexus and implications to regional anaesthesiologist. International Journal of Regional Anaesthesia. 2021;2(2). doi:10.13107/ijra.2021.v02i02.036

Drake RL, Vogl AW, Mitchell A, eds. Gray’s Anatomy for Students. 5th ed. Elsevier - Health Sciences Division; 2023.

Hansen JT. Netter’s Clinical Anatomy. 5th ed. Elsevier - Health Sciences Division; 2022.