A patient presents with loss of ankle dorsiflexion and a high-stepping gait characterized by foot slap. Which nerve injury best explains this presentation?

• A. Severing of the common peroneal nerve
• B. Anterior compartment syndrome
• C. Hip flexor weakness
• D. Calcaneal spurring

Answer: (A)

Docusing on the nerves that move the ankle, loss of dorsiflexion points to dysfunction of the muscles that lift the front of the foot (primarily tibialis anterior), which are innervated by the deep branch of the peroneal (fibular) nerve, with the overall common peroneal nerve providing the critical motor supply to dorsiflexors and foot evertors. When the common peroneal nerve is severed, these dorsiflexors fail, producing foot drop. The resulting gait is a high-stepping pattern used to clear the foot during swing, and at heel strike the foot may slap down abruptly because the foot cannot dorsiflex eccentrically to control plantarflexion.

The other options don’t fit this classic pattern. Anterior compartment syndrome can damage similar nerves but is a local, painful condition with acute signs rather than a nerve injury pattern. Hip flexor weakness affects the hip, not dorsiflexion. Calcaneal spurring causes heel pain and impaired push-off, not a loss of dorsiflexion or a foot-drop gait.