Pediatric musculoskeletal disorders Quiz: Ace Your Exams

A 12-year-old boy is brought to his pediatrician for evaluation of an abnormal gait. The patient first noticed a dull pain in his left medial thigh and knee three weeks ago and reports it has been difficult to bear weight on the left leg over the past week. He has no history of trauma to the leg or hip. He had an upper respiratory tract infection one month ago. Temperature is 37°C (98.6°F), pulse is 82/min, and blood pressure is 116/72 mm Hg. The patient is at the 50th percentile for height and 95th percentile for weight. Physical examination demonstrates an antalgic gait. The physician reproduces the pain with flexion, external rotation, and abduction of the left hip. A left hip radiograph with a frog-leg lateral view is demonstrated below. Which of the following is the most likely diagnosis?
 

^{Reproduced from: Radiopaedia}