Flank pain radiating to l...

A previously healthy 14-year-old girl presented with a reported inability to bear weight on her right leg. Approximately 1 month before, she twisted her body while standing on her right leg and felt a painful pop in her back. This pain was mild but worsened 3 days before admission, localizing to her right flank with radiation to her lower back. She was afebrile and denied any groin pain or previous musculoskeletal injury or surgery. 

Examination: On examination, she had tenderness to palpation about the right lower quadrant of the abdomen and lower back and had pain with a straight leg raise test but had a relatively pain-free hip range of motion. She had no neurologic deficits. Initial radiographs of the right hip and lumbar spine were unremarkable. Her C-reactive protein level was 14.8 mg/L (normal 0–3.2); erythrocyte sedimentation rate, 28 mmol/h (normal 0–20 mmol/h); and white blood cell count, 13,600/uL. MRI was taken. Five days later, the culture results were positive for methicillin-susceptible Staphylococcus aureus.