Aspirate a suspected septic hip in a child — OSCE

A 3-year-old previously well boy is brought to the emergency department refusing to walk. He is febrile at 39.1°C, holds the right hip flexed and abducted, and cries when the hip is moved. The C-reactive protein is 95 mg per litre, the white cell count is 16,000 per microlitre, and an ultrasound shows a right hip effusion. You are the paediatric registrar asked to score the risk, prepare for an ultrasound-guided hip aspiration, and outline the technique, the fluid handling, the complications and the disposition.