Review Question - QID 214870

A 6-year-old male presents with worsening right knee pain and progressive difficulty with ambulation over the last 3 days. He reports falling down on his knee weeks ago but did not scrape his skin in his recollection. He denies any fevers or chills. On examination, the right knee is erythematous and swollen, but has minimal pain with passive range of motion. His laboratory studies are significant for WBC count of 9,300 cells/mm3 (reference <11,000 cells/mm3), ESR 35 mm/hr (reference <15 mm/hr), and CRP 12.2 mg/L (reference <10 mg/L). What is the most appropriate next step in management?