Which finding is most consistent with deep peroneal nerve injury?

Which finding is most consistent with deep peroneal nerve injury?

• A. Inability to plantarflex the foot
• B. Loss of sensation on the heel
• C. Normal leg strength
• D. Inability to dorsiflex the foot

Answer: (D)

The deep peroneal nerve supplies the muscles of the anterior leg that lift the foot (dorsiflexion) and extend the toes, notably the tibialis anterior, extensor digitorum longus, and extensor hallucis longus. When this nerve is injured, dorsiflexion is weakened or lost, leading to a classic foot drop pattern. This is the most direct and reliable sign of deep peroneal nerve dysfunction, since the action it controls is precisely what’s impaired. In contrast, plantarflexion is performed mainly by the tibial nerve via the gastrocnemius-soleus complex, so inability to plantarflex would point to tibial nerve injury rather than the deep peroneal nerve. Loss of sensation on the heel involves the tibial distribution, not the deep peroneal, and normal leg strength would be inconsistent with a motor nerve lesion in the deep peroneal distribution. Thus, difficulty in dorsiflexion best matches deep peroneal nerve injury.

The deep peroneal nerve supplies the muscles of the anterior leg that lift the foot (dorsiflexion) and extend the toes, notably the tibialis anterior, extensor digitorum longus, and extensor hallucis longus. When this nerve is injured, dorsiflexion is weakened or lost, leading to a classic foot drop pattern. This is the most direct and reliable sign of deep peroneal nerve dysfunction, since the action it controls is precisely what’s impaired.

In contrast, plantarflexion is performed mainly by the tibial nerve via the gastrocnemius-soleus complex, so inability to plantarflex would point to tibial nerve injury rather than the deep peroneal nerve. Loss of sensation on the heel involves the tibial distribution, not the deep peroneal, and normal leg strength would be inconsistent with a motor nerve lesion in the deep peroneal distribution. Thus, difficulty in dorsiflexion best matches deep peroneal nerve injury.