Review Question - QID 108118

A 14-year-old previously healthy male presents to your office with complaints of two months of dull, aching pain in his right leg that has recently become worse. While he experiences the pain constantly, he notes that it is sometimes so bad at night that it awakes him from his sleep. Though an avid soccer player, he has been unable to participate this season due to the pain and difficulty running. He cannot think of any particular trauma that might have precipitated this pain. Vitals are all within normal range. Physical examination reveals localized tenderness below the knee with mild swelling and reduced range of motion. You order an X-ray of the painful limb, which is shown in Figure A. What is the most likely diagnosis?