Femoral nerve

The femoral nerve is one of two major nerves supplying the lower limb.

Gross anatomy

It arises from posterior divisions of L2-L4 roots of the lumbar plexus and provides motor supply to the anterior compartment of the thigh and sensory supply to the hip, anterior and medial thigh, knee, and medial leg (as the saphenous nerve).

Course

Intra-abdominal

• emerges from the lateral border of the psoas muscle to descend between the iliacus and psoas muscles
• sends a motor branch to iliacus before passing under the inguinal ligament 

Femoral triangle

• lies above iliacus, outside and lateral to the femoral sheath
• sends a branch to pectineus 
• the lateral femoral circumflex artery separates the nerve into superficial and deep divisions
• the terminal branch of the deep division reaches the apex of the femoral triangle to become the saphenous nerve

Superficial division

Branches of the superficial division include:

• nerve to sartorius
• medial cutaneous nerve of thigh: contributes to subsartorial plexus (with branches of obturator and saphenous nerves)
• intermediate cutaneous nerve of thigh
• sympathetic vasomotor supply to blood vessels

Deep division

Branches of the deep division include:

• nerve to rectus femoris: also receives articular supply from hip
• nerve to vastus lateralis: also receives articular supply from knee 
• nerve to vastus intermedius
• nerve to vastus medius: also receives articular supply from knee
• continues as the saphenous nerve, which passes behind sartorious

Saphenous Nerve

• runs within the subsartorial canal, giving off an infrapatellar branch (it also contributes to the subsartorial nerve plexus)
• curves behind sartorius, appearing behind the medial knee
• accompanies great saphenous vein, along posterior border of tibia
• passes over lower aspect of tibia to appear anterior to the medial malleolus
• runs along dorsum of foot
• provides sensation as far as the first metatarsal-phalangeal joint

Variant anatomy

• femoral nerve splits into two or three separate slips within the psoas muscle but unite to descend as a single bundle ²
• accessory femoral nerve: fibres arise separately in lumbar plexus, passes anterior to femoral nerve, may terminate as saphenous nerve / cutaneous branch
• femoral branch replacing lateral femoral cutaneous nerve (usually comes directly off lumbar plexus)
• saphenous nerve terminating  at knee with distribution replaced b branch of tibial nerve

Related pathology

Femoral nerve is endangered by trauma. Injury results in weakness of thigh extension and numbness overlying the anterior/medial thigh and medial leg.

The femoral nerve is responsible for the patellar tendon reflex (tests L3-L4 spinal component)

• femoral nerve neuropathy