Femoral nerve

The femoral nerve is a major peripheral nerve of the lower limb, originating from the lumbar plexus.

Origin

The femoral nerve is formed within the substance of the psoas major muscle by the union of the posterior divisions of the anterior rami of the L2, L3, and L4 spinal nerves. (Note: The anterior divisions of these roots contribute to the obturator nerve.)

Course

• The femoral nerve emerges from the lower lateral border of the psoas major muscle.

• It descends between the psoas major and iliacus muscles, lying over the anterior surface of iliacus and underneath the iliacus fascia.

• Positioned lateral to the femoral artery, the femoral nerve passes deep to the inguinal ligament, entering the anterior compartment of the thigh in the femoral triangle.

Before passing the inguinal ligament, the nerve gives motor branches to the iliacus (L2-L3). Upon entering the thigh, it sends a branch to the pectineus muscle (L2-L3). At this point, it divides into superficial and deep divisions, separated by the lateral circumflex femoral artery.

Branches & Distribution

a) Superficial (or Anterior) Division

• Motor: Supplies the sartorius muscle (L2-L3).

• Sensory: Divides into the medial and intermediate cutaneous branches, which provide sensory innervation to the skin of the anterior and medial surfaces of the thigh.

b) Deep (or Posterior) Division

• Motor: Provides branches to the quadriceps muscles (L3-L4), which include: Rectus femoris Vastus medialis Vastus intermedius Vastus lateralis.

• Sensory: The saphenous nerve (L3-L4) is the terminal branch of the deep division. It travels in the adductor canal beneath the sartorius muscle and then becomes subcutaneous at the medial knee. It provides cutaneous innervation to: The medial surface of the leg, the medial ankle and the medial side of the foot.

• Articular Innervation: Sensory articular branches from the deep (or posterior) division supply the hip and knee joints.

Reflex

The patellar tendon reflex (commonly tested in clinical exams) is mediated by the femoral nerve through its motor innervation to the quadriceps muscles.

Clinical Relevance

Damage to the femoral nerve (neuropathy) can lead to:

• Weakness or paralysis of the quadriceps muscles, resulting in difficulty extending the knee, and to some extend difficulty extending the hip as well, due to involvement of the iliacus and pectineus muscles.

• Loss of sensation over the anterior and medial thigh, medial leg, and foot (due to involvement of medial and intermediate cutaneous nerves, and the saphenous nerve)

• Absence of the patellar reflex.