A patient sustains a fracture of the fibular neck. He cannot dorsiflex or evert the foot and walks with a high-stepping gait. Sensation is lost over the first web space dorsum but the sole is spared. Which structure explains why plantar flexion remains normal?

• A Plantar flexion is supplied by the deep peroneal nerve, which escapes injury
• B Gastrocnemius receives dual innervation from both peroneal divisions
• C Plantar flexors are supplied by the tibial nerve, which is not affected by a fibular neck lesion ✓
• D Plantar flexion is a purely reflex movement independent of peripheral nerves

Explanation

At the fibular neck only the common peroneal nerve is injured. It divides into the deep peroneal nerve (dorsiflexion via tibialis anterior, toe extension, first web space sensation) and the superficial peroneal nerve (eversion via peroneus longus and brevis). Plantar flexion depends on gastrocnemius, soleus, and other calf muscles supplied by the tibial nerve, which runs behind the medial malleolus and is untouched here. The sparing of sole sensation distinguishes this from a sciatic or tibial nerve lesion.

Reference: Gray's Anatomy for Students / standard orthopaedic texts, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.