Injury to which nerve can cause foot drop and sensory loss on the lateral leg?

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

Answer: (C)

Foot drop comes from loss of dorsiflexion, which is carried out by muscles supplied from the common peroneal nerve (via its deep peroneal branch). This nerve wraps around the fibular neck, making it a common site of injury. When it is damaged, dorsiflexors fail and the foot cannot lift the front end, producing foot drop. At the same time, the common peroneal nerve provides cutaneous branches to the lateral leg (via the lateral sural cutaneous branch), so sensory loss occurs in that lateral leg region. In contrast, tibial nerve injury would mainly affect plantarflexion and the sole, the femoral nerve would affect thigh muscles and sensation, and the sural nerve would cause sensory loss to part of the leg/foot without causing foot drop. Thus, the common peroneal nerve best explains both phenomena.