femoral nerve

The femoral nerve arises from the posterior divisions of the L2-L4 ventral rami, passes through the psoas major, and travels within the false pelvis before entering the thigh lateral to the femoral artery and vein under the inguinal ligament (femoral triangle: from lateral to medial - Nerve, Artery, Vein, Lymphatics = NAVEL). Motor innervation includes the iliacus and pectineus (hip flexion), sartorius, and the quadriceps femoris group (rectus femoris, vastus lateralis, medialis, intermedius) for knee extension. Sensory innervation covers the anterior and medial thigh via anterior cutaneous branches, and the medial leg and foot via the saphenous nerve (a terminal sensory branch that accompanies the great saphenous vein).

Clinical significance: Femoral nerve injury results in weakness of knee extension and hip flexion, causing difficulty climbing stairs or rising from a seated position, and loss of the patellar reflex (knee-jerk, L2-L4). Common causes include pelvic or femoral fractures, retroperitoneal hematoma (e.g., in anticoagulated patients or psoas hematoma), stab/gunshot wounds, prolonged lithotomy position during surgery, and iatrogenic injury during femoral vessel catheterization or hip/pelvic surgery. Diabetic femoral neuropathy (diabetic amyotrophy) can cause proximal weakness and pain. Sensory loss follows the femoral nerve distribution and saphenous nerve territory. Femoral nerve blocks are used clinically for anesthesia in hip and knee surgeries, targeting the nerve as it exits the pelvis lateral to the femoral artery.

Anatomical relationships are tested via the mnemonic NAVEL (lateral to medial in femoral triangle: Nerve, Artery, Vein, Empty space, Lymphatics), important for procedures like central venous catheterization to avoid nerve injury.