Review Question - QID 213773

A 12-year-old boy is brought to the clinic for evaluation of right leg pain for the past 2 months. He reports that the pain is concentrated in the right knee area and sometimes radiates towards the thigh. It is especially worse at night and has been waking him up from sleep for the past week or so. His mom reports that the patient has been having trouble climbing up and down the stairs and has been limping while he walks. The patient denies any headaches, night sweats, chills, weight loss, or trauma but endorses subjective fevers and shortness of breath, especially on exertion. A physical examination demonstrates a left-leaning limp with moderate tenderness at the right patella and proximal leg. Both active and passive range of motion are intact, and there is no obvious swelling, erythema, or deformities. A radiograph of the right knee was obtained and is shown in Figure A. What is the most likely explanation for this patient’s presentation?