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acute foot drop


  • acute foot drop is an uncommon presentation to the ED but often represents a genuine time critical emergency
  • foot drop is due to acute weakness of tibialis anterior (TA)
  • foot dorsiflexors are typically innervated by the L5 nerve root, but there may be considerable segmental overlap and anatomical variations, adding to the complexity of innervation
  • Most leg muscles have a dual root innervation, and usually TA is innervated primarily by L4 and secondarily by L5. EHL and EDL are primarily innervated by L5 and secondarily by L4 and S1.
  • TA and EHL are innervated by the L5 root in 90% of people
  • up to 10% of the population have an anatomical variant in which the S1 root innervates these muscles
  • it is important to differentiate from a flail foot in which NO movements at the ankle joint are possible and this represents a more extensive problem such as stroke (CVA) or cauda equina syndrome (CES)
  • there may be only a small window of opportunity to have a successful outcome
  • compartment syndrome must be recognized and treated WITHIN HOURS at most to minimise permanent deficits
  • cauda equina syndrome (CES) must be managed neurosurgically within 24-48hrs to minimise permanent deficits


  • ischaemia of tibialis anterior with local pain
  • peroneal nerve mononeuropathy (the most common cause, and is usually painless)
    • pressure on the nerve around the head of the fibula
    • trauma
    • nerve entrapment
    • infection (eg. syphilis)
    • space occupying lesions
    • diabetes
    • iatrogenic injury
  • L4 or L5 nerve root radiculopathy with decreased reflexes and usually with back pain and rarely, may cause acute bilateral foot drop
  • UMN spinal cord pathology with brisk reflexes
  • intracranial causes - usually with other neurology of the leg and possibly ipsilateral arm
    • a parasagittal brain lesion may affect the leg area of the motor cortex and result in an isolated paraparesis
    • lesions in other areas where nerve fibres are highly condensed:
      • corona radiata
      • internal capsule (lacune)
      • cerebral peduncle (lacune)
      • medulla
      • spinal cord pyramidal tract (myelopathy)
foot_drop.txt · Last modified: 2020/01/28 12:08 by

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