A child with fever, hip pain and limp

A previously well 12-year-old boy presented after 1 month of increasing right-sided hip pain with a limp, decreased energy and a 2-kg weight loss. He had no history of trauma, other joint problems, recent travel or contact with ill people. He had no abdominal pain or change in his bowel habits. In the patient, Crohn's disease was only suspected after finding an abscess.