A patient has foot drop, loss of dorsiflexion and eversion, and sensory loss over the dorsum of the foot and lateral lower leg. Inversion and plantar flexion are preserved. The lesion is in the:

• A Common peroneal nerve at the fibular neck ✓
• B Superficial peroneal nerve
• C Deep peroneal nerve
• D Sciatic nerve at the gluteal region

Explanation

Loss of both dorsiflexion (tibialis anterior = deep peroneal) and eversion (peroneus longus and brevis = superficial peroneal), combined with sensory loss over the lateral lower leg and dorsum of the foot, indicates a lesion of the common peroneal nerve proximal to its division at the fibular neck. Inversion (tibialis posterior, tibial nerve) and plantar flexion (gastrocnemius, tibial nerve) are preserved, excluding sciatic nerve injury which would additionally cause hamstring weakness and sensory loss over the sole. Deep peroneal nerve alone causes foot drop but spares eversion and lateral leg sensation.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.