A 35-year-old woman presents 6 weeks after a FOOSH injury with persistent wrist pain, swelling, and clicking. Repeat radiographs at 2 weeks showed a non-displaced fracture of the scaphoid waist. She was immobilized in a thumb spica cast for 4 weeks but removed it early due to discomfort. On current examination, anatomical snuffbox tenderness persists, and there is mild loss of grip strength. What is the most likely complication, and what is the appropriate imaging to assess it?