Which nerve injury most commonly causes foot drop due to dorsiflexion weakness?

Which nerve injury most commonly causes foot drop due to dorsiflexion weakness?

• A. Tibial nerve
• B. Common peroneal nerve
• C. Superficial peroneal nerve
• D. Sural nerve

Answer: (B)

Foot drop happens when the muscles that lift the front of the foot (the dorsiflexors, mainly tibialis anterior) are weak. These muscles are controlled by the deep branch of the common peroneal nerve. The common peroneal nerve itself is particularly vulnerable where it crosses the fibular neck, so injury to it is a common way dorsiflexion gets impaired. When dorsiflexion is weak, you can’t bring the foot up during a step, leading to a steppage gait. In contrast, the tibial nerve mainly controls plantarflexion and inversion, so its injury would not typically present as foot drop. The superficial peroneal nerve affects eversion and sensation over part of the foot but not dorsiflexion. The sural nerve is sensory and wouldn’t cause motor weakness. So injury to the common peroneal nerve best explains dorsiflexion weakness and foot drop.

Foot drop happens when the muscles that lift the front of the foot (the dorsiflexors, mainly tibialis anterior) are weak. These muscles are controlled by the deep branch of the common peroneal nerve. The common peroneal nerve itself is particularly vulnerable where it crosses the fibular neck, so injury to it is a common way dorsiflexion gets impaired. When dorsiflexion is weak, you can’t bring the foot up during a step, leading to a steppage gait.

In contrast, the tibial nerve mainly controls plantarflexion and inversion, so its injury would not typically present as foot drop. The superficial peroneal nerve affects eversion and sensation over part of the foot but not dorsiflexion. The sural nerve is sensory and wouldn’t cause motor weakness. So injury to the common peroneal nerve best explains dorsiflexion weakness and foot drop.