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lateral popliteal nerve palsy

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The common peroneal nerve represents a major nerve terminal of the sciatic nerve

  • the nerve is divided into two main branches when it pierces the peroneus longus muscle to reach the anterior compartment of the lower leg
    • deep peroneal nerve
      • supplies the muscles that control foot dorsiflexion and toe extension (tibialis anterior, extensor digitorum longus, peroneus tertius, and extensor hallucis longus)
        • tibialis anterior is the strongest contributor to foot dorsiflexion while , extensor digitorum longus, peroneus tertius also assist
      • in the foot it supplies the short toe extensors, the extensor digitorum brevis, and extensor hallucis brevis. sensory branch supplies the interspace between the first and second toes
    • superficial peroneal nerve 
      • supplies  the peroneus longus and brevis
      • supplies sensation to the skin of the lateral leg and the dorsum of the foot and toes (sparing the small area between the first two toes and a variable lateral part of the foot) (1,2)

aetiology ( peroneal nerve lesions) (2)

Peroneal nerve is the most commonly damaged nerve in the lower limb and is relatively unprotected as it traverses the lateral aspect of the head of the fibula.

Damage of the nerve may occur due to various reasons:

  • acute trauma
    • may result from - direct blows and lacerations, severe adduction injuries and dislocations of the knee, fractures of the head or neck of the fibula, and bullet wounds

  • external pressure
    • most frequent cause of peroneal neuropathy
    • caused by
      • nerve compression as a result of  sleeping in an abnormal position
      • weight loss and pressure caused by hard hospital mattresses or bed railings as seen in bed ridden and comatose patients
      • plaster casts and leg braces
      • sitting cross-legged – in habitual leg crossers
      • squatting or kneeling for a long period of time e.g - farm labourers and other workers such as carpet layers 

  • injury during knee operations, including total knee replacement and arthroscopic surgery

  • masses e.g. - a ganglion arising from the superior tibiofibular joint,  Baker’s cysts etc

  • mononeuropathy multiplex syndromes 

  • idiopathic causes

Clinical features include:

  • foot drop
  • weakness of dorsiflexion and eversion of the foot
  • weakness of extensor hallucis longus
  • inversion and plantar flexion are normal
  • anaesthesia over the lower lateral part of the leg and dorsum of the foot; often with little or no sensory loss
  • all reflexes are intact - the ankle jerk is lost in a sciatic nerve lesion
  • wasting of the anterior tibial and peroneal muscles

Recovery occurs within a few weeks when the cause is simple compression. Full knee flexion should be avoided as in kneeling or squatting, and the patient should not sit with the legs crossed over the unaffected leg. To prevent foot drop the patient should wear an aluminium night-shoe at night and during the day, a shoe with plastic inserts.

Surgical exploration is indicated if the weakness progresses or fails to resolve within 1-2 months, or if there is an obvious local lesion.

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