Which motor function is commonly affected by a fibular neck (common peroneal) nerve injury?

Which motor function is commonly affected by a fibular neck (common peroneal) nerve injury?

• A. Dorsiflexion and toe extension
• B. Plantarflexion
• C. Inversion
• D. Eversion

Answer: (A)

When the common peroneal nerve is injured at the fibular neck, the muscles that lift the foot and extend the toes lose their nerve supply. The deep branch of this nerve powers the tibialis anterior and the toe-extensor muscles, so dorsiflexion and toe extension become weak or lost, producing the classic difficulty in lifting the front of the foot (foot drop). Plantarflexion is controlled by the tibial nerve, which is usually intact, so pushing the foot downward remains possible. Inversion is also primarily tibial nerve–driven, so that function is typically preserved. Eversion can be affected because peroneal muscles contribute to it, but the most characteristic and widely observed deficit is the loss of dorsiflexion and toe extension, making that function the best answer.

When the common peroneal nerve is injured at the fibular neck, the muscles that lift the foot and extend the toes lose their nerve supply. The deep branch of this nerve powers the tibialis anterior and the toe-extensor muscles, so dorsiflexion and toe extension become weak or lost, producing the classic difficulty in lifting the front of the foot (foot drop). Plantarflexion is controlled by the tibial nerve, which is usually intact, so pushing the foot downward remains possible. Inversion is also primarily tibial nerve–driven, so that function is typically preserved. Eversion can be affected because peroneal muscles contribute to it, but the most characteristic and widely observed deficit is the loss of dorsiflexion and toe extension, making that function the best answer.