A 28-year-old man presents with acute onset fever (38.9°C), severe pain in the right femur, and inability to bear weight. On examination, there is localized swelling and warmth over the mid-femur. ESR is 85 mm/hr and CRP is 12 mg/dL. X-ray of the femur is normal. Blood culture is pending. What is the most appropriate next step in management?