The femoral nerve is the largest branch of the lumbar plexus (L2-L4), emerging from the lateral border of psoas major and passing beneath the inguinal ligament in the lateral femoral sheath compartment. It supplies the anterior thigh muscles (iliacus, pectineus, quadriceps femoris, sartorius) and the skin of the anterior thigh and medial leg via the saphenous nerve.
| Origin | Lumbar plexus (L2, L3, L4) |
|---|---|
| Course | Emerges from the lateral border of psoas, descends in the groove between psoas and iliacus, passes behind the inguinal ligament lateral to the femoral artery and outside the femoral sheath, and divides in the femoral triangle into anterior and posterior divisions |
| Motor | |
| Sensory |
|
Femoral neuropathy produces quadriceps weakness, absent knee jerk, and anterior thigh numbness. Common causes include retroperitoneal haematoma (anticoagulated patients), femoral artery catheterisation injury, lithotomy position stretch, and psoas compartment pathology. Femoral nerve block at the femoral triangle level provides analgesia for hip and knee surgery. The landmark is the femoral artery at the inguinal ligament with the nerve lying lateral. Ultrasound-guided block improves accuracy. ASIS-level numbness (lateral femoral cutaneous nerve) spares the quadriceps and indicates meralgia paresthetica rather than femoral neuropathy.
Quadriceps weakness, absent knee reflex, and anterior thigh numbness from inguinal or retroperitoneal compression.
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