Review Question - QID 210509

A 16-year-old boy presents to his primary care physician with left knee pain. He reports a 3-month history of mild progressive chronic knee pain that is not associated with activity. He is an active soccer player and reports that his knee pain is affecting his ability to run. He has a history of mild intermittent asthma and uses an albuterol inhaler as needed. His temperature is 98.6°F (37°C), blood pressure is 115/60 mmHg, pulse is 65/min, and respirations are 16/min. Physical examination reveals a healthy, well-appearing boy in no acute distress. There is small palpable mildly tender mass on the medial inferior left knee. A knee radiograph is shown in Figure A. A biopsy of this patient's condition would most likely reveal which of the following findings?