A 72-year-old man is brought to the emergency room after injuring his right knee in a car accident. The pain started soon after the accident. Later that same day he developed swelling and more intense pain making walking difficult. On physical examination, the knee is warm, swollen, and extremely painful to bend. There are clinical signs of an effusion. X-rays of the knee rule out a fracture, and joint fluid aspiration reveals an opaque-colored fluid containing rhomboid crystals with weak-positive birefringence. Which of the following is the most appropriate next step in management?