Nerves of the lower limb

The nerves of the lower limb originate from the lumbosacral plexus.

The Lumbosacral Plexus

The lumbosacral plexus is made up of two separate plexuses.

• Supplies the whole of the lower limb

• • 1. Lumbar plexus (ventral rami of T12-L4) – supplies the anterior and medial compartments
       • Obturator nerve – supplies the adductors (i.e. the medial compartment)
       • Femoral nerve – supplies the quadriceps, sartorius (anterior compatment of thigh)

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    2. Sacral plexus (ventral rami of L4-S3) – this has 2 main sets of nerves
       • Also contributes to the femoral nerve
       • Gluteal nerves  (posterior compartment of hip)
         1. Superior gluteal nerve
         2. Inferior gluteal nerve
       • Sciatic nerve and its branches  (posterior thigh + all of lower leg)
         1. Tibial nerve – calf muscles
         2. Common Peroneal nerve
            1. Deep fibular – anterior compartment
            2. Superficial fibular – lateral compartment
         3. Sciatic branches

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• Both plexuses partially come together to form the lumbosacral trunk
  • Forms only from L4 and L5 (i.e. upper sacral/lower lumbar plexus)
  • Forms from the anterior divisions
  • This gives off the femoral nerve

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Nerves of the leg

Lumbar plexus

• Femoral nerve  (L2-L4) branches into:
  1. Lateral femoral cutaneous nerve
     • Supplies the lateral aspect of the thigh.
     • Clinically important
       • Typically damaged in compression from lumbar lordosis – commonly in pregnancy
  2. Saphenous nerve
     • Purely sensory supply
     • Ends around the knee

The femoral nerve is typically damaged in trauma. This results in quadriceps palsy causing knee extension failure

• Obturator nerve (L2-L4)
  • Supplies hip adductors
  • Injury causes loss of hip adduction

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Sacral plexus

• Superior gluteal nerve
  • Supplies the gluteus medius, minimus, and TFL
  • Injury causes trendelenburg sign, a waddling gait

• Inferior gluteal nerve
  • Innervates gluteus maximus
  • Injury is rare but causes loss of gluteus maximus muscle – difficult standing up.

• Sciatic nerve (L4-S3)
  • Injured in many pathologies:
    • Causes loss of all muscle function below the knee due to loss of sciatic branches.
  • Splits into tibial and common peroneal  nerves in the popliteal fossa. 
  • Common fibular nerve (aka common peroneal nerve)
    • Injury results in foot drop due to loss of anterior muscles this extensor failure
    • Superficial fibular nerve innervates 2 muscles  laterally
    • Deep fibular nerve
      • Supplies the anterior lower leg
      • Minimal sensory supply to a bit of the foot
  • Tibial nerve
    • Supplies all the muscles of the calf (i.e. posterior compartment)
    • Injured in tarsal tunnel syndrome.
    • Splits at the ankle to form the plantar nerves
      

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