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)
      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 nervecalf muscles
          2. Common Peroneal nerve
            1. Deep fibular – anterior compartment
            2. Superficial fibular – lateral compartment
          3. Sciatic branches

 

 

 

 

 

 

 

 

 

  • 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

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

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