If you are interested in learning more about clinical decision rules, the Ottawa Ankle Rule is a simple and world famous example, which was developed in Ottawa and tested in many Canadian centres including Queen’s. It looks at patients who have had a simple inversion or eversion injury and uses one historical feature (“inability to weight bear”) and 4 physical findings (bony tenderness in four specific places) to guide a decision about whether or not to perform an xray to look for a fracture.