Review Question - QID 211271

An 11-year-old male presents to the emergency department after injuring his right knee when he collided with another player at basketball practice. His mother reports that he has had a cold for the past 3 days, but is otherwise healthy. He has been unable to bear weight following the injury. On exam, he has pain localized over the distal femoral physis, a palpable effusion, and moderate discomfort as you take his knee through a range of motion. Distally, he is neurovascularly intact. Initial workup reveals a temperature of 98.5°F, WBC 9k, CRP 1.7 mg/dL, and an ESR of 33. A radiograph obtained in the ED is shown in Figure 1. Which of the following is the best next step in treatment?