What nerves innervate the lateral, medial, and posterior leg?

Innervation of the Lateral, Medial, and Posterior Leg

The lateral leg is primarily innervated by the superficial peroneal nerve, the medial leg by the saphenous nerve, and the posterior leg by the tibial nerve and its branches, including the sural nerve and posterior femoral cutaneous nerve. 1, 2

Lateral Leg Innervation

• Superficial Peroneal Nerve
  • Origin: Branch of common peroneal nerve (which itself is a division of the sciatic nerve)
  • Root derivation: L4-S1
  • Course: Travels in the lateral compartment of the leg between peroneus longus and brevis muscles
  • Provides:
    • Motor innervation to peroneus longus and brevis muscles
    • Sensory innervation to most of the lateral leg and dorsum of foot
  • Danger zone: Anterior to lateral malleolus where it becomes superficial 3

Medial Leg Innervation

• Saphenous Nerve
  • Origin: Terminal sensory branch of femoral nerve
  • Root derivation: L3-L4
  • Course: Travels with great saphenous vein along medial aspect of leg
  • Provides: Sensory innervation to medial leg and medial foot to the first metatarsal
  • Danger zone: Around medial malleolus where it's vulnerable during surgery 3

Posterior Leg Innervation

• Tibial Nerve

  • Origin: Larger terminal branch of sciatic nerve
  • Root derivation: L4-S3 (primarily from ventral branches L4, L5, S1-S3) 4
  • Course: Travels through popliteal fossa, then deep to gastrocnemius and soleus
  • Provides:
    • Motor innervation to posterior compartment muscles (gastrocnemius, soleus, tibialis posterior, flexor digitorum longus, flexor hallucis longus)
    • Sensory innervation via its branches
  • Terminal branches: Divides into medial and lateral plantar nerves in the tarsal tunnel 4

• Sural Nerve

  • Origin: Usually formed by branches from both tibial and common peroneal nerves
  • Course: Descends between heads of gastrocnemius, becomes superficial in distal third of leg
  • Provides: Sensory innervation to posterolateral leg and lateral foot
  • Danger zone: Posterior to lateral malleolus 3, 2

• Posterior Femoral Cutaneous Nerve

  • Origin: Sacral plexus (S1-S3)
  • Traditionally thought to innervate only the posterior thigh
  • Recent evidence shows it extends much further distally than previously thought
  • Contributes significantly to sensory innervation of the posterior leg, with termination at the proximal or distal lower leg in 90.3% of cases 5
  • Often follows the small saphenous vein (in 90.3% of cases) 5

Clinical Significance

1. Nerve Blocks:

   • Understanding these innervation patterns is crucial for effective regional anesthesia
   • Incomplete blocks of the lower leg may occur if the posterior femoral cutaneous nerve contribution is not considered 5

2. Surgical Approaches:

   • Danger zones exist around both malleoli where cutaneous nerves are vulnerable 3
   • Surgical procedures should account for these nerve distributions to prevent iatrogenic injury

3. Nerve Compression Syndromes:

   • Tarsal tunnel syndrome: Compression of the tibial nerve in the tarsal tunnel 4
   • "Jogger's heel" and other entrapment neuropathies can occur at predictable anatomical sites 2

4. Nerve Transfers:

   • In high sciatic nerve injuries, branches from the tibial nerve (to gastrocnemius and soleus) can be used as donors to restore function of the deep peroneal nerve 6

5. Imaging Considerations:

   • MRI is the mainstay for imaging nerve pathology in the lower extremity 1
   • Ultrasound can help differentiate nerves from adjacent vasculature 2

Understanding these innervation patterns is essential for diagnosing and treating various neuropathies, planning surgical approaches, and performing effective nerve blocks in the lower leg.