Review Question - QID 216628

A 42-year-old man presents to his primary care physician with a 1-month history of back and leg pain. He says that he was lifting a box at work when he felt a sharp pain in his back. Since then, he has noticed that he has intermittent severe pain that shoots down his left leg. He also noticed that he is stumbling more often and falls on occasion. His temperature is 98.6°F (37.0°C), blood pressure is 135/79 mmHg, pulse is 80/min, and respirations are 14/min. On physical exam, he is unable to lift the great toe of his left foot and has decreased 2-point discrimination over the lateral lower leg. Raising his right leg leads to pain in his left leg that radiates past his left knee. Which of the following is the most likely cause of this patient's symptoms?