A 13-year-old boy presents to his primary care physician with a four-week history of a limp and intermittent, dull pain in his left knee and groin. The pain is worse at the end of the day and after playing sports. His mother notes that he seems to be walking with his left foot turned outwards. There is no history of significant trauma. He is otherwise healthy, with his growth charts indicating he is at the 96th percentile for weight. His past medical history and family history are unremarkable. His vital signs are normal.