Femoral nerve
Nervus femoralis
Also known as: saphenous nerve
The largest branch of the lumbar plexus (L2–L4, posterior divisions). It passes beneath the inguinal ligament lateral to the femoral artery to supply the anterior thigh muscles, including quadriceps, and the skin of the anterior thigh. Its saphenous branch supplies the medial leg and foot.
Overview
The femoral nerve emerges from the lateral border of psoas and descends in the groove between psoas and iliacus, supplying iliacus. It passes deep to the inguinal ligament into the thigh through the lacuna musculorum. Here it lies lateral to the femoral artery and outside the femoral sheath. Its relative position is given by "NAVY" (Nerve, Artery, Vein, Y-fronts/empty space, from lateral to medial).
About 4 cm below the ligament, in the femoral triangle, it breaks into a spray of branches:
• anterior (superficial) branches: sartorius, pectineus, and the medial and intermediate cutaneous nerves of the thigh;
• posterior (deep) branches: the four parts of quadriceps femoris, articular branches to the hip and knee, and the saphenous nerve.
The saphenous nerve is its longest and only branch below the knee. It accompanies the femoral vessels through the adductor canal, emerges between sartorius and gracilis at the medial knee, and runs with the great saphenous vein to supply the skin of the medial leg and the medial border of the foot.
- Location
Posterior abdominal wall (between psoas and iliacus) → under the inguinal ligament → femoral triangle → anterior thigh; the saphenous branch continues to the medial leg and foot.
Anatomy
- Innervation
- Motor: iliacus, pectineus (often shared with the obturator nerve), sartorius and quadriceps femoris.
• Sensory: the anterior and medial thigh, the medial knee, leg and ankle, and the medial border of the foot (saphenous).- Nerve roots
L2, L3, L4 (posterior divisions).
- Course
Lateral border of psoas → groove between psoas and iliacus (deep to the iliac fascia) → deep to the inguinal ligament, lateral to the femoral artery and outside the femoral sheath → femoral triangle → divides into anterior and posterior branches. The saphenous nerve passes through the adductor canal → medial knee → alongside the great saphenous vein → medial leg and foot.
- Branches
- Muscular branches: iliacus, pectineus, sartorius, rectus femoris, vastus lateralis, vastus intermedius and vastus medialis.
• Anterior cutaneous branches of the thigh (medial and intermediate cutaneous nerves).
• Articular branches to the hip and knee.
• Saphenous nerve, including the infrapatellar branch.- Relations
- In the iliac fossa: between psoas and iliacus, behind the iliac fascia (the basis of the fascia iliaca block).
• In the femoral triangle: lateral to the femoral artery.
• In the adductor canal: the saphenous nerve lies anterolateral to the femoral artery.
Function
- Extension of the knee (quadriceps), essential for standing, climbing stairs and rising from a chair
- Hip flexion (iliacus, rectus femoris, sartorius, pectineus)
- Sensation of the anterior and medial thigh and the medial leg and foot
- Afferent and efferent limbs of the patellar reflex (L3–L4)
Clinical significance
Femoral neuropathy
Causes include retroperitoneal or iliacus haematoma (anticoagulants), pelvic and hip surgery, femoral arterial catheterisation, the lithotomy position and diabetic amyotrophy. The findings are:
• weak knee extension, so the knee buckles, especially on stairs;
• weak hip flexion, if the lesion is above the inguinal ligament;
• absent patellar reflex;
• sensory loss over the anterior thigh and medial leg.
An L4 radiculopathy, by contrast, also weakens hip adduction (obturator) and ankle dorsiflexion.
Femoral nerve block
Local anaesthetic injected lateral to the femoral pulse below the inguinal ligament, or a fascia iliaca block, provides excellent analgesia for hip fractures and anterior thigh and knee surgery. Saphenous nerve injury during varicose vein stripping or knee arthroscopy causes medial leg numbness.
Mnemonics
Femoral triangle contents (lateral → medial)
"NAVY": Nerve, Artery, Vein, Y-fronts (or the empty space of the femoral canal with its lymphatics).
Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.