Review Question - QID 109984

A 51-year-old man presents to the emergency room after being the victim of a robbery and assault. He was walking down an alley when he was approached by a stranger with a knife. Upon resisting, the stranger stabbed the patient’s right distal forearm before stealing his wallet and evading the scene. The patient was able to call an ambulance and has remained conscious despite mild bleeding from the injury site. He reports severe pain in his forearm and an inability to move his 2nd and 3rd fingers. He has no medical conditions and takes no medications. He is allergic to penicillin and ibuprofen. On exam, the patient is able to flex the proximal interphalangeal (PIP) joints of his 2nd through 5th fingers. When the PIP joints of his 2nd through 5th fingers are restrained by the examiner, flexion is noted at the DIP joints of the 4th and 5th fingers but not the 2nd and 3rd digits. Thumb flexion at the metacarpophalangeal (MCP) joint and interphalangeal (IP) joint is preserved. Sensation is intact over the palmar and dorsal aspects of the radial and ulnar hand. This patient most likely has an injury to which of the following muscle tendons?