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A 56 yo male presents to you with a complaint of foot drop. He is a manual labourer and has had multiple episodes of blunt trauma to his lower limbs and has also complained of lower back pain over the last few months.

How can you differentiate a peripheral nerve, versus, root cause, versus central cause?

Causes of Foot Drop

  • Common Peroneal Nerve palsy
  • Sciatic Nerve Palsy
  • Lumbosacral Plexus Lesion
  • L5 Root lesion
  • Peripheral Neuropathy
  • Distal Myopathy
  • Motor Neuron Disease
  • Stroke


The Sciatic Nerve L4,5 S1,2 supplies all muscles below the knee and hamstrings

Common Peroneal Nerve L4,5 S1, is a terminal branch of the Sciatic nerve and supplies the anterior and lateral muscles of the leg.

The Ankle Jerk Reflex

Bend the ankle and the knee. Externally rotate the thigh. Hold the foot in dorsiflexion and let the tendon hammer fall onto the Achilles tendon.

The patient can kneel on a bed or chair and the tendon hammer allowed to fall on the Achilles tendon.

The ankle is bent back and the foot held in dorsiflexion, with the hand pushing up on the sole of the foot. The tendon Hammer is allowed to fall onto the back of the hand, which is contact with the sole of the foot.

The response should be a plantar flexion of the foot and contraction of the gastrocnemius muscle.

How does the Ankle Jerk Help Us?


L5 Lesion


Common Peroneal Lesion


Upper Motor Neurone Lesion

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