<qa>  What is the Canadian C-Spine Rule comprised of?Background: Physicians in Canadian emergency departments EDs annually treat 185,000 alert and stable trauma victims who are at risk for cervical spine c-spine injury. Only 0.9 of these patients have, however, suffered a cervical spine fracture. Current use of radiography is not efficient. More than 98 of c-spine radiographs are negative and there is considerable variation among hospitals and physicians in radiography use. C-spine radiographs are little ticket items, low cost procedures that significantly add to health care costs due to high volume. In addition, alert and stable trauma patients are often immobilized on a backboard with a rigid collar and sandbags for many hours. This leads to considerable patient discomfort and unnecessary use of valuable time and space in our crowded EDs. This renewal application builds on previous MRCCIHR grants to determine feasibility phase 0, MRC GR-13304D, 1995-96, develop a decision rule for c-spine radiography phase I, MRC MT-13700, 1996-99, N8,924, and prospectively validate this Canadian C-Spine Rule phase II, CIHR MT13700, 1999-2002, N8,000, all part of the University of Ottawa Group Grant in Decision Support Techniques CIHR 2000-143. The Canadian C-Spine Rule is comprised of simple clinical variables Figure 1 and allows physicians to be much more selective in ordering radiography JAMA 2001. In the recently completed prospective validation phase II, we confirmed the accuracy and reliability of the rule. 