An 18-year-old patient presents with an acutely swollen and tender right knee. Vital signs show a heart rate of 115 beats/min, respiration rate of 18 breaths per minute, blood pressure of 130/80 mm Hg, and temperature of 38. C. The knee is swollen, red, and has an effusion. No other joints are involved. There is no skin rash, penile discharge, or heart murmur. There is non-tender hepatomegaly, cervical lymphadenopathy, and pharyngitis with white tonsillar exudates. Which of the following steps would be most appropriate in the management of this patient?