A 3-year-old boy presents to the emergency department (ED) with a 1-day history of severe pain on the right side of the neck. On the day of presentation the patient woke up in the morning with his head turned to the right and indicating pain to the right side of his neck. The parent reports that the patient is unable to flex his neck completely and walks with a hunched posture. Two weeks before presentation the patient started having right shoulder pain and an inability to completely raise his right arm a day after visiting a water park, but the family denies any traumatic event. The patient was first taken to his pediatrician and then to a local emergency department, where radiographic studies of his right upper extremity were negative for any bony pathology. The patient followed up at an orthopedic clinic, where repeated radiography of his right extremity was...

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