“It’s just a muscle sprain”

A 10 year old boy presented to his general practitioner with a four week history of left mid-thigh pain with no associated history of systemic symptoms. He had no memory of a preceding trauma and no history of infection, locally or systemically. The pain was relapsing and remitting in its extent and frequency. It was also activity related, with occasional night waking and pain at rest. His GP took a full history, conducted a complete hip examination, and at initial presentation decided that the pain was caused by a muscle sprain.

Two months later the pain has not abated and the child re-presented to his GP, who requested a plain radiograph of the hip, the results of which were normal. A further three months later, his father noticed an associated distal thigh mass and immediately took the boy to the emergency department. On presentation to hospital, he was walking pain free but had an obvious mass, which did not limit his range of movement.

He did not have a fever; his C reactive protein was 6 mg/L, erythrocyte sedimentation rate was 4 mm in the first hour, and total white blood cell count was 8×10⁹/L. The on-call orthopaedic team requested anterioposterior and lateral radiographs of the thigh (figs 1⇓ and 2⇓).