Fourth Lumbar Nerve (Left)

Origin

The fourth lumbar nerve originates in, or just lateral, to the intervertebral foramen, inferior to the fourth lumbar vertebra. Here, the anterior and posterior roots combine to form the first lumbar nerve proper.

Course

The fourth lumbar nerve gives off a posterior ramus, that runs to the epaxial musculature and skin of the lower back, and an anterior ramus, that runs inferior and laterally to the lumbar and sacral plexuses.

Branches

The fourth lumbar nerve gives off a posterior ramus and contributes to three branches through the anterior ramus. These include the femoral and obturator nerves, nerve to quadratus femoris, and superior gluteal nerve. The fourth lumbar nerve, along with the fifth, form the lumbosacral trunk, which runs to the sacral plexus, thus, the fourth lumbar nerve fibers contribute to the sciatic nerve.

Supplied Structures

The posterior ramus of the fourth lumbar nerve supplies the epaxial muscles of the lumbar region, including erector spinae and transversospinal muscles. In addition to cutaneous innervation of the skin over the lower back.

The anterior ramus of the fourth lumbar nerve contributes to the lumbar plexus and the following nerves and their targets.

—Small branches innervate the iliopsoas muscle.

—The femoral nerve arises from the second, third, and fourth lumbar nerves. It innervates psoas, iliacus, pectineus, sartorius, and quadriceps muscles (rectus femoris, vastus lateralis, vastus intermedius, and vastus medialis). Sensory innervation of the femoral nerve is received from the anterior and medial thigh.

—The obturator nerve arises from the second, third, and fourth lumbar nerves. It innervates the adductor muscles (gracilis, obturator externus, adductor longus, adductor brevis, and adductor magnus). Sensory innervation of the obturator nerve is received from skin of the medial thigh.

The anterior ramus of the fourth lumbar nerve also contributes to the sacral plexus via the lumbosacral trunk, and subsequently the following nerves and their targets.

—The superior gluteal nerve arises from the fourth and fifth lumbar nerves, as well as the first sacral nerve. It innervates the gluteus medius, gluteus minimus, and tensor fasciae latae muscles. This nerve does not contain a sensory component.

—The sciatic nerve is the longest nerve in the body. It gives rise to the common fibular, tibial, and sural nerves. It arises from the fourth and fifth lumbar nerves as well as the first, second, and third sacral nerves. The sciatic nerve innervates all the muscles of the posterior thigh, anterior and posterior leg, and foot. Sensory innervation of the sciatic nerve is received from the leg and foot. The fourth lumbar nerve carries sensory information primarily from the anterior thigh and knee. Of the muscles innervated by the sciatic nerve, the tibialis anterior is primarily innervated by the fourth lumbar nerve.

List of Clinical Correlates

—Trendelenburg sign

—Sciatica

—Disc herniation

—Lumbar stenosis