Lumbar plexus

The lumbar plexus is formed by the ventral rami of the lumbar spinal nerves (L1-L4) and is located within the psoas major muscle. It gives rise to several important nerves that innervate the lower limb and some abdominal muscles. Here are the main nerves, their paths, and innervations:

  1. Iliohypogastric Nerve (L1)

    • Path: Passes across the quadratus lumborum, then goes toward the anterior abdominal wall.

    • Innervation: Supplies skin over the lower abdomen and part of the gluteal area; innervates the transversus abdominis and internal oblique muscles.

  2. Ilioinguinal Nerve (L1)

    • Path: Courses along the iliac crest and pierces the internal oblique muscle.

    • Innervation: Provides sensory innervation to the skin of the groin and scrotum (or labia) and motor innervation to the abdominal muscles.

  3. Genitofemoral Nerve (L1-L2)

    • Path: Pierces the psoas major; divides into genital and femoral branches.

    • Innervation:

      • Genital Branch: Supplies the cremaster muscle and skin of the medial thigh in males; innervates the labia in females.

      • Femoral Branch: Provides sensory innervation to the skin of the upper anterior thigh.

  4. Femoral Nerve (L2-L4)

    • Path: Passes beneath the inguinal ligament into the thigh.

    • Innervation: Supplies the quadriceps muscle (primary knee extensor), iliopsoas, and other muscles; provides sensory innervation to the anterior thigh and medial aspect of the leg via the saphenous nerve.

  5. Obturator Nerve (L2-L4)

    • Path: Passes through the obturator foramen to enter the medial compartment of the thigh.

    • Innervation: Supplies the adductor muscles of the thigh (adductor longus, adductor brevis, and part of adductor magnus) and skin over the medial thigh.

  6. Lateral Femoral Cutaneous Nerve (L2-L3)

    • Path: Passes under the inguinal ligament, lateral to the iliopsoas.

    • Innervation: Provides sensory innervation to the skin of the lateral thigh.

  7. Accessory Obturator Nerve (L3-L4) (present in some individuals)

    • Path: Runs adjacent to the obturator nerve.

    • Innervation: Supplies the pectineus muscle and contributes to the obturator nerve supply.

  8. Lumbosacral Trunk (L4-L5)

    • Path: Descends into the pelvis to participate in the formation of the sacral plexus.

    • Innervation: Contributes fibers to the sciatic nerve and other pelvic nerves.

Understanding the lumbar plexus is crucial for recognizing its role in providing motor and sensory functions to the lower body, particularly in clinical settings and for regional anesthesia procedures.