Review Question - QID 213669

A 42-year-old woman presents to urgent care with right radial wrist pain. She reports slipping on an icy driveway yesterday and landing on her outstretched right hand. On physical exam, the skin is intact, and there is edema and focal tenderness at the dorsoradial wrist, at the base of the thumb. Distal sensation is intact, range of motion and strength testing are limited by pain. Radiographs are negative for fracture, and the patient is sent home with ibuprofen and ice packs. Two days later, she returns and her pain, tenderness, and edema have worsened. Which of the following is the patient at greatest risk for as a complication of her injury?