Review Question - QID 219569

A 39-year-old recreational tennis player presents to the clinic as a referral from her primary care physician for chronic pain in the dorsum of her wrist. She notes activity-related pain over the area demonstrated in Figure A that has worsened since she started training with a new tennis pro four times per week. On exam in the office, the patient's pain is recreated with ulnar deviation of the wrist while she grasps the affected thumb in her fist and is relieved when the thumb is extended. She has failed rest, bracing, and two corticosteroid injections and comes with the ultrasound findings in Figure B. Which of the following nerves innervates the most likely affected structures in this patient's condition?