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Common Peroneal Nerve Palsy — RACP Adult Medicine MCQ

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EasyNeurologyCommon Peroneal Nerve PalsyRACP Adult Medicine

A 68-year-old man with type 2 diabetes presents with a new right foot drop. Examination shows weakness of ankle dorsiflexion and eversion with sensory loss over the lateral leg and dorsum of the foot. Knee jerk is preserved. What is the site of nerve involvement?

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Correct answer: E — Tibial nerve

Foot drop with weakness of ankle dorsiflexion and eversion (peroneal muscles) with sensory loss over the lateral leg and dorsal foot, and preserved knee jerk (L3/4 – femoral nerve), localises to the common peroneal (fibular) nerve at the fibular head. The nerve is vulnerable to compression at this superficial site (leg crossing, prolonged bed rest, casts, weight loss). NCS/EMG confirms the diagnosis and distinguishes it from L5 radiculopathy (which additionally causes ankle inversion weakness and may have back pain). In diabetes, mononeuropathy is common.

Reference: eTG – 2025 – Neurology