Review Question - QID 2281

Figure 1 is the radiograph of a 5-year-old male who presents to the ED with right hip pain. The patient’s parents report that he was recently diagnosed with an upper respiratory infection, but began having hip pain this morning. Initially, he was unable to walk secondary to pain, but can now ambulate with a limp. His temperature is 99.5°F, ESR 20 mm/hr, CRP 9 mg/L (normal range, 0-10mg/L). On exam, he has limited internal rotation of the right hip. What is the most likely diagnosis?