An atypical limping teenager.

A 13-year-old boy presented with a 5-day history of left-sided limp of gradual onset. There was no history of trauma. He developed a fever and rigours a few days before presenting to the paediatric emergency department. On examination, he was tender on palpating the left gluteal area on active mobilisation of the left hip and could not weight bear on the left leg. Pelvic X-rays and ultrasound of the left hip were normal. The blood results showed raised inflammatory markers and normal white cell count. The blood cultures were positive for Staphylococcus aureus. On day 2, a left hip MRI was performed as well as CT-guided drainage. Diagnosis of left sacroiliac septic arthritis was made. After an initial lack of improvement under intravenous ceftriaxone, a drain was inserted and left in situ for 8 days with double intravenous antibiotic therapy instituted. The patient made a full recovery. 2015 BMJ Publishing Group Ltd.