Femoral nerve !

The femoral nerve is the main nerve of the front of the thigh; it powers the quadriceps that straighten the knee and carries feeling.

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What it is

A large nerve from the lower spine (lumbar plexus). It runs down beside the psoas, passes under the inguinal ligament next to the femoral artery, and branches out in the front of the thigh.

What it does

Controls the quadriceps (straightening the knee) and helps lift the thigh. It carries feeling from the front of the thigh and, through the saphenous nerve, from the inner leg.

Key facts

Roots: L2–L4 (posterior divisions, lumbar plexus)
Moves: Iliacus, pectineus, sartorius, quadriceps femoris; knee extension (knee jerk L3–L4)
Feeling from: Anterior and medial thigh (anterior cutaneous branches); medial leg and foot (saphenous nerve)

Relations

Course: Forms within the psoas major, emerges from its lateral border, descends in the groove between the psoas and iliacus beneath the fascia iliaca, passes under the inguinal ligament lateral to the femoral sheath and splits in the femoral triangle into anterior and posterior divisions
Medial: The femoral artery, then the femoral vein and the femoral canal, all inside the femoral sheath; above the inguinal ligament the psoas major separates it from the external iliac artery, and under the ligament the iliopectineal arch does, so it passes through the muscular lacuna
Deep: The iliopsoas in the iliac fossa and in front of the hip
Superficial: The fascia iliaca, the inguinal ligament and, below it, the fascia lata
Lateral: The iliacus and, near the anterior superior iliac spine, the lateral femoral cutaneous nerve

How to find it

Below the inguinal ligament the femoral pulse is felt at the mid-inguinal point (halfway from the anterior superior iliac spine to the pubic symphysis). The nerve lies just lateral to the pulse, deep to the fascia iliaca, and is found there with ultrasound for a femoral block.

Examination

Patellar reflex (L3–L4, mainly L4): reduced or absent in a femoral nerve or L4 root lesion
Resisted knee extension and a single-leg step-up: quadriceps weakness; if hip adduction (obturator nerve) is also weak, the lesion is more likely at the L3–L4 roots or the lumbar plexus
Femoral nerve stretch test (prone knee bend): anterior thigh pain when the knee is bent with the hip extended suggests irritation of an L2–L4 root

On imaging

Ultrasound below the inguinal ligament shows it as a flat, honeycomb-like structure lateral to the femoral artery, under the fascia iliaca; this view guides the femoral block. Above the ligament CT is first if an iliopsoas haematoma is suspected, a classic cause of femoral palsy. MRI shows denervation oedema or atrophy in the quadriceps. Radiographs do not show it.

Common problems

Injury or stretching during hip, pelvic or abdominal surgery, or pressure from bleeding in the pelvis.
Weak quadriceps: the knee may buckle and climbing stairs is hard.
Numbness at the front of the thigh and the inner leg.

How it is diagnosed

Physical exam (knee reflex, thigh strength, feeling); nerve conduction studies and EMG; imaging to look for a cause such as a bleed.

Treatment

Treating the cause, such as relieving pressure on the nerve.
Physical therapy and a knee brace while the nerve recovers.
Numbing medicine placed near this nerve (a nerve block) is often used to control pain after knee or hip surgery.

Clinical notes

Iatrogenic injury from self-retaining retractor blades in abdominal and pelvic surgery, the lithotomy position, anterior hip approaches and femoral artery puncture
Femoral and fascia iliaca blocks are used for hip fractures and thigh or knee surgery; the quadriceps weakness they cause raises the risk of falls
Diabetic lumbosacral radiculoplexus neuropathy (diabetic amyotrophy) starts with severe thigh pain followed by quadriceps wasting and can mimic a femoral neuropathy

Development

Formed from the posterior divisions of the ventral rami of L2–L4, it supplies muscles of the dorsal muscle mass; the medial rotation of the lower limb in the seventh week carries that mass, and the nerve, to the front of the thigh.

Memory aid

NAVEL, from lateral to medial in the groin: Nerve, Artery, Vein, Empty space (femoral canal), Lymphatics.

Guillain-Barré syndrome

Test yourself

Think of the answer, then tap the question to see it.

What are the roots of the femoral nerve?

L2–L4, posterior divisions of the lumbar plexus.

How does the femoral nerve relate to the femoral sheath under the inguinal ligament?

It is the most lateral of the femoral group and lies outside the sheath, lateral to the femoral artery.

How does hip flexion help localise a femoral nerve lesion?

A lesion above the inguinal ligament also weakens hip flexion (iliacus); below it, hip flexion is spared.

Which reflex is reduced in a femoral nerve lesion?

The patellar (knee) reflex, L3–L4, mainly L4.

What sensory territory does the femoral nerve supply?

The anterior and medial thigh, and through the saphenous nerve the medial leg and foot.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): nervus femoralis TA2 6522
Official Spanish (DeCS): Nervio femoral DeCS D005267
English (TA2): Femoral nerve

Sources: Terminologia Anatomica (TA2); DeCS; Anatomy, Bony Pelvis and Lower Limb: Thigh Femoral Nerve; 8.5 Development of the Appendicular Skeleton (OpenStax (Rice University), 2022) · adapted, CC BY 4.0; Anatomía humana (4.ª ed.), tomo 1, cap. 70: Nervios del plexo lumbosacro.

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Representative model, for educational purposes only.

Femoral nerve highlighted on the Durgical 3D model