MSFinals-4432

A 6-year-old girl arrives at the emergency department with intense pain in her left hip and an inability to bear weight. Her parents are worried about the potential for an infection. She had a cold a week ago, but has since recovered. She seems to be in good health. There has been no hip trauma. Blood tests show normal WBC and ESR levels. An ultrasound of the hip reveals a slight effusion in the joint capsule. What is the best course of action now?