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Femoral nerve

The femoral nerve is the largest branch of the lumbar plexus. It arises from the posterior divisions of the anterior rami of L2, L3, and L4 spinal nerves. It supplies motor innervation to the anterior thigh muscles and sensory innervation to the anterior and medial thigh, as well as the medial leg and foot via the saphenous nerve.

The femoral nerve is clinically significant in regional anesthesia, orthopedic and vascular surgery, and in evaluating neuropathies.

Synonyms

  • Nervus femoralis

  • Crural nerve (historical term)

  • Lumbar plexus major branch

Origin, Course, and Branches

  • Origin: Posterior divisions of L2–L4 spinal nerves within the lumbar plexus

  • Course:

    • Emerges from the lateral border of the psoas major muscle

    • Descends between the psoas major and iliacus within the iliac fossa

    • Passes beneath the inguinal ligament to enter the thigh, lateral to the femoral artery

    • Divides into multiple motor and sensory branches in the femoral triangle

  • Branches:

    • Motor branches: Supply iliacus, pectineus (partly), sartorius, quadriceps femoris group

    • Sensory branches: Supply anterior thigh skin and medial leg/foot (via saphenous nerve)

    • Saphenous nerve: Longest branch, providing sensory innervation to medial leg and foot

Relations

  • Lies lateral to the psoas major in the pelvis

  • In the femoral triangle, lies lateral to the femoral artery and vein

  • Covered anteriorly by fascia iliaca

  • Related inferiorly to inguinal ligament and hip joint capsule

Function

  • Motor: Extension of the knee (quadriceps femoris), flexion of the hip (iliacus, sartorius, pectineus)

  • Sensory: Skin of anterior thigh, medial leg, and medial foot

  • Reflex: Afferent and efferent limb of the patellar reflex

Clinical Significance

  • Vulnerable to injury in pelvic fractures, retroperitoneal hemorrhage, or compression beneath the inguinal ligament

  • Femoral neuropathy causes weakness of knee extension and sensory loss in anterior/medial thigh and medial leg

  • Target for femoral nerve block in anesthesia and pain management

  • Important landmark in vascular surgery (lies lateral to femoral artery)

MRI Appearance

T1-weighted images:

  • Nerve appears as a low-to-intermediate signal linear structure surrounded by bright fat in iliac fossa and femoral triangle

T2-weighted images:

  • Nerve shows intermediate to mildly hyperintense signal compared to muscle

  • Pathological nerves (neuropathy, neuritis) appear more hyperintense

STIR (Short Tau Inversion Recovery):

  • Normal nerve shows low signal

  • Inflamed or edematous nerve appears bright hyperintense

T1 Fat-Sat Post-Contrast:

  • Normal nerve: minimal or no enhancement

  • Pathologic nerve: focal or diffuse enhancement in neuritis, tumor, or infiltration

3D T2 SPACE / CISS:

  • Nerve shows intermediate to mildly hyperintense signal relative to muscle

  • Surrounded by bright fat or CSF, which highlights the nerve’s course

  • Excellent for tracing nerve along iliacus, beneath inguinal ligament, and into femoral triangle

CT Appearance

Non-Contrast CT:

  • Nerve not directly visualized; inferred as a thin soft tissue structure within fat of iliac fossa and femoral triangle

  • Surrounding fat provides contrast for localization

Post-Contrast CT:

  • Nerve itself does not enhance significantly

  • Pathology (tumors, hematoma, infection) may appear as soft tissue thickening or mass along its expected course

MRI image

Femoral nerve MRI axial anatomy image-img-00000-00000

MRI image

Femoral nerve mri coronal image