Q. A 9-year-old is brought to the physician's office for left groin pain for the past 3 months. The pain increases with activities and relieves by taking rest. His mother also noticed that he has been limping for the last 2 weeks. There is no history of fever, rash, or trauma and he is otherwise in good health. His temperature is 98.2°F, heart rate is 83 beats per minute, blood pressure is 110/70 mm of Hg and respiratory rate is 15 per minute. Physical examination shows limited abduction and internal rotation of his left leg. Both hips are normal. Deep tendon reflexes are brisk, pulses are normal, and muscle strength testing shows 5/5 bilaterally. Laboratory tests are shown below. A plain X-ray of the pelvis shows widening of hip joint spaces and subchondral fracture in the left hip. What is the most likely diagnosis for this patient?