Anatomy Atlas

Femoral nerve

Nervus femoralis
NerveHigh-yielddraftNeuroMSK

Largest branch of the lumbar plexus (L2–L4), supplying the hip flexors and knee extensors and the skin of the anterior thigh and medial leg. Lesions cause knee buckling and a lost patellar reflex.

Core anatomy

Location

Anterior thigh; enters the thigh under the inguinal ligament lateral to the femoral artery.

Root values

Posterior divisions of the ventral rami of L2–L4.

Origin

Lumbar plexus, within psoas major

Course

Emerges from the lateral border of psoas, runs between psoas and iliacus (supplying iliacus), passes under the inguinal ligament lateral to the femoral sheath (it is not in the sheath) into the femoral triangle, and divides after a few centimeters into anterior and posterior branches.

Branches
  • Muscular: iliacus, pectineus, sartorius and quadriceps femoris
  • Anterior cutaneous nerves of the thigh
  • Saphenous nerve: the longest cutaneous branch; runs through the adductor canal, emerges at the medial knee, and runs with the great saphenous vein to the medial leg and medial foot
  • Articular branches to the hip and knee
Motor

Hip flexion (iliacus, sartorius, rectus femoris) and knee extension (quadriceps).

Sensory

Anterior and medial thigh; medial leg and medial foot (saphenous).

Relations

Order in the femoral triangle from lateral to medial: Nerve, Artery, Vein, (Empty space), Lymphatics — NAVEL.

Muscles innervated

  • Adductor muscles of the thigh — obturator nerve (L2–L4) for most; pectineus mainly by the femoral nerve; the hamstring part of adductor magnus by the tibial division of the sciatic nerve
  • Quadriceps femoris — femoral nerve (L2–L4)

Other structures innervated

Found in

Mentioned in

Generated automatically from links in other entries.

Lower limb dermatomes (anterior view) and key musclesL1 over the groin and upper thigh; L2 the upper anterior thigh; L3 the lower anterior thigh and knee; L4 the medial leg and medial malleolus; L5 the lateral leg and dorsum of the foot including the great toe; S1 the lateral edge of the foot and little toe. Table: L2 hip flexion; L3 knee extension; L4 ankle dorsiflexion and patellar reflex; L5 great toe extension; S1 plantarflexion and ankle reflex.L1L2L3L4L5S1LateralMedial (great toe)ASIA key sensory point (S1: lateral heel)RootKey muscle actionReflexL2Hip flexion—L3Knee extension—L4Ankle dorsiflexionPatellar (L3–L4)L5Great toe extension—S1Ankle plantarflexionAnkle (Achilles)Foot drop with weak inversion → L5 root;with normal inversion → common fibular nerve.Maps differ between sources; neighbours overlap.

Swipe sideways to see the whole diagram →

Lower limb dermatomes and key muscles. Right lower limb, anterior view (medial = your right). Dots are ASIA key sensory points; the table gives the key muscle action and reflex for each root. Dermatome maps differ between sources.
Original schematic, created for this atlas.
Femoral triangle (right, anterior view)The femoral triangle of the right thigh, with lateral on the left. Its base is the inguinal ligament, from the anterior superior iliac spine to the pubic tubercle; its lateral border is sartorius and its medial border adductor longus, which meet at the apex, where the adductor canal begins. The floor is iliopsoas laterally and pectineus medially. From lateral to medial lie the femoral nerve outside the femoral sheath, then inside the sheath the femoral artery, the femoral vein and the femoral canal, with the deep inguinal lymph nodes most medially (NAVEL). The great saphenous vein joins the femoral vein through the saphenous opening, below and lateral to the pubic tubercle. The deep femoral artery leaves the femoral artery a few centimetres below the ligament and runs posteriorly.ASISInguinal ligamentFemoral nerveDeep femoral arteryIliopsoas (floor)SartoriusApex → adductor canalPubic tubercleFemoral arteryFemoral veinFemoral canal (ring)Deep inguinal nodesSaphenofemoral junctionPectineus (floor)Adductor longusGreat saphenous veinLateral ←→ MedialNAVEL, lateral → medialDashed outline = femoral sheath

Swipe sideways to see the whole diagram →

Femoral triangle (right, anterior view). Lateral on your left. The base is the inguinal ligament, the borders are sartorius (lateral) and adductor longus (medial), and the floor is iliopsoas and pectineus. Lateral to medial: Nerve (outside the femoral sheath), Artery, Vein, Empty space (femoral canal), Lymphatics. The pulse is felt just below the mid-inguinal point, with the vein just medial to it; a femoral hernia comes through the femoral canal.
Original schematic, created for this atlas.
Posterior abdominal wall showing the lumbar plexus in psoas with the femoral, obturator, lateral femoral cutaneous and other branches
The lumbar plexus: the femoral nerve emerging from psoas.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 823. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))
Surface projection of the femoral artery and femoral nerve on the front of the thigh from the inguinal ligament to the adductor tubercle
Surface markings of the femoral nerve and artery.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 1245. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))
Anterior view of the lower limb showing the cutaneous nerves, including the saphenous, superficial and deep fibular (peroneal) and sural branches
Cutaneous nerves of the front of the lower limb, including the saphenous nerve.
Henry Vandyke Carter, Gray's Anatomy of the Human Body, 20th ed. (1918), Fig. 825. Source · Public domain (Public domain in the US: published before January 1, 1931 (per Wikimedia Commons))

Clinical correlations

Femoral neuropathy PANCE

Mechanism / lesion

Retroperitoneal/iliopsoas hematoma (anticoagulation, hemophilia), pelvic or hip surgery (retractor compression, lithotomy positioning), diabetic amyotrophy, femoral artery catheterization.

Classic presentation

Weak knee extension (knee buckles, trouble with stairs), weak hip flexion (if the lesion is proximal), absent/reduced patellar reflex, and numbness of the anterior thigh and medial leg. Hip adduction is preserved — weakness there suggests an L3/L4 root or plexus lesion instead.

Saphenous nerve injury

Mechanism / lesion

Great saphenous vein harvest or stripping, knee arthroscopy or surgery.

Classic presentation

Numbness or pain of the medial leg and foot without weakness.

Femoral nerve block

Mechanism / lesion

Local anesthetic injected lateral to the femoral artery below the inguinal ligament (ultrasound guided).

Classic presentation

Analgesia for hip fractures and knee surgery; causes temporary quadriceps weakness (fall risk).

High-yield PANCE pearls

  • Femoral nerve: L2–L4, knee extension, patellar reflex (L4).
  • Anticoagulated patient + groin/flank pain + knee buckling → iliopsoas hematoma compressing the femoral nerve.
  • Weak adduction too → think L3–L4 root/plexus, not isolated femoral nerve.
  • NAVEL — lateral to medial in the femoral triangle.

Imaging anatomy

CT

CT abdomen/pelvis for retroperitoneal or iliopsoas hematoma.

MRI

Lumbosacral plexus/MR neurography; lumbar spine MRI to exclude L3/L4 radiculopathy.

Ultrasound

Identifies the nerve lateral to the femoral artery for blocks; shows groin hematomas and pseudoaneurysms after catheterization.

Physical exam

Surface landmarks

Just below the midpoint of the inguinal ligament, about 1 cm lateral to the femoral pulse.

Strength / function testing

Resisted knee extension, hip flexion; patellar reflex (L4); sensation over the anterior thigh and medial leg (saphenous). Compare hip adduction (obturator) to localize.

Femoral nerve stretch test (reverse straight-leg raise)

Technique

Prone; flex the knee and extend the hip.

Positive test

Pain in the anterior thigh.

Significance

Suggests upper lumbar (L2–L4) root irritation.

Self-quiz

Q1.

A 66-year-old man on warfarin with an INR of 5.8 has right groin and flank pain. His right knee gives way when walking, the right patellar reflex is absent, and he has numbness over the anterior thigh. Hip adduction is normal. What is the most likely cause?

Show answer

B

Supratherapeutic anticoagulation can cause a retroperitoneal/iliopsoas hematoma that compresses the femoral nerve — quadriceps weakness, lost patellar reflex and anterior thigh numbness, with normal adduction (obturator nerve spared). Confirm with CT.

Q2.

Which structure in the femoral triangle lies outside the femoral sheath?

Show answer

C

The femoral nerve lies lateral to and outside the femoral sheath, which contains the femoral artery, vein and canal (lymphatics); the femoral branch of the genitofemoral nerve does pierce the sheath's lateral part.

Q3.

After great saphenous vein harvest for bypass surgery, a patient has numbness of the medial leg and foot with no weakness. Which nerve was injured?

Show answer

D

The saphenous nerve, the longest cutaneous branch of the femoral nerve, runs with the great saphenous vein below the knee to the medial leg and foot. It is purely sensory, so injury causes numbness without weakness.

Q4.

The patellar reflex mainly tests which nerve root, carried by which nerve?

Show answer

B

The patellar (knee-jerk) reflex is mediated mainly by L4 through the femoral nerve (L2–L4) to the quadriceps. The ankle reflex is S1 (tibial nerve).

Q5.

A patient has weak knee extension, a reduced patellar reflex and weak hip adduction. Where is the lesion most likely?

Show answer

C

The femoral nerve doesn't supply the adductors (obturator nerve), so added adduction weakness points to a lesion of the shared L3–L4 roots or the lumbar plexus. An isolated femoral neuropathy preserves hip adduction.

Flashcards

See also