Courtesy: Amr Abdelgawad, Maimonaides Medical Centre, Brooklyn, New York, USA

Femoral Nerve (L2–L4)

• Origin: Lumbar plexus roots L2, L3, L4.
• Motor supply: Quadriceps femoris, iliacus, sartorius, and part of pectineus.
• Primary function: Knee extension and hip flexion.
• Located lateral to the femoral sheath (which contains the femoral artery and vein).
• Travels within the iliopsoas muscle before entering the thigh.
• Compression may occur due to bleeding within the iliopsoas (e.g., hemophilia).
• Differentiating femoral nerve palsy from L3 radiculopathy: test hip adductors (obturator nerve).

Sciatic Nerve (L4–S3)

• Largest nerve in the body.
• Origin: L4, L5, S1, S2, S3 nerve roots.
• Exits pelvis through the greater sciatic foramen below the piriformis muscle.
• Course: deep to piriformis, posterior to external rotators, superficial to quadratus femoris.
• Runs deep to the long head of biceps femoris in the thigh.
• Divides into tibial nerve and common peroneal nerve.

Lateral Femoral Cutaneous Nerve

• Pure sensory nerve from the lumbar plexus.
• Passes under the inguinal ligament.
• Runs between sartorius and tensor fasciae latae.
• Pierces fascia lata to become cutaneous.
• At risk during anterior hip approaches.
• Compression causes meralgia paresthetica.

Tibial Nerve

• Terminal branch of the sciatic nerve.
• Supplies all posterior thigh muscles except the short head of biceps femoris.
• In the leg it supplies posterior compartment muscles: gastrocnemius, soleus, tibialis posterior, flexor digitorum longus, flexor hallucis longus.
• Divides into medial and lateral plantar nerves in the foot.
• Responsible for plantarflexion and toe flexion.

Common Peroneal (Fibular) Nerve

• Branch of the sciatic nerve.
• Supplies the short head of the biceps femoris in the thigh.
• Wraps around the neck of the fibula.
• Divides into deep peroneal and superficial peroneal nerves.
• Highly vulnerable to injury at the fibular neck.
• Stretch increased with knee extension and reduced with knee flexion.

Deep Peroneal Nerve

• Supplies anterior compartment of the leg.
• Muscles: tibialis anterior, extensor hallucis longus, extensor digitorum longus, peroneus tertius.
• Responsible for ankle dorsiflexion and toe extension.
• Provides sensation to the first dorsal web space.

Superficial Peroneal Nerve

• Supplies lateral compartment muscles: peroneus longus and peroneus brevis.
• Responsible for foot eversion.
• Provides sensory innervation to most of the dorsum of the foot.
• Terminates as medial and intermediate dorsal cutaneous nerves.
• Emerges through fascia about 12 cm above the lateral malleolus.

Sural Nerve

• Formed by contributions from the tibial nerve and common peroneal nerve.
• Runs in the posterior calf.
• Provides sensation to the posterolateral leg and dorsolateral foot.
• Small saphenous vein lies medial to the nerve.
• During surgery retracting the vein laterally helps protect the nerve.

Baxter’s Nerve

• Also called the first branch of the lateral plantar nerve.
• Supplies the abductor digiti minimi muscle.
• Can be compressed beneath the abductor hallucis muscle.
• Entrapment causes medial heel pain.
• Often misdiagnosed as plantar fasciitis.
• Tinel’s sign may be present over the nerve.

Saphenous Nerve

• Largest cutaneous branch of the femoral nerve.
• Travels in the adductor canal.
• Infrapatellar branch supplies anterior knee skin.
• Sartorial branch becomes superficial between sartorius and gracilis.
• Commonly injured during medial knee surgeries such as ACL graft harvesting.

Important Root-Level Functions

• L4: tibialis anterior (ankle dorsiflexion) and patellar reflex.
• L5: extensor hallucis longus and gluteus medius.
• S1: gastrocnemius, soleus, and lateral compartment muscles; Achilles reflex.
• S2: perianal sensation.

Dermatomal Sensation of the Foot

• L4: medial foot and great toe.
• L5: dorsum of foot and toes 2–4.
• S1: lateral foot and little toe.

Reflexes

• Patellar tendon reflex: L4.
• Achilles tendon reflex: S1.
• No reliable reflex for L5.