A 2 year old girl has been brought by Mum the day after falling down 5 carpetted steps at home. She is unable to walk. she indicates that her knee hurts.

On examination both legs look the same there is no swelling or bruising. She has a full range of passive movement at the hip, knee and ankle. She has no tenderness, although you think her expression changes slightly on tibial palpation. she will attempt to walk over to the toys but fails

You decide to do an X-ray of the lower limb.