 Methods: We propose a matched-pair cluster design study which compares outcomes during 3 consecutive 12-month before, after, and decay periods at 6 pairs of intervention and control sites Figure 3. These 12 hospital ED sites will be stratified as teaching or community hospitals, matched according to baseline c-spine radiography ordering rates, and then allocated within each pair to either intervention or control groups. During the after period at the intervention sites, simple and inexpensive strategies will be employed to actively implement the Canadian C-Spine Rule: a physician group discussion and consensus, b educational initiatives lecture, posters, pocket cards, and c a process-of-care modification with a mandatory reminder of the Rule at the point of requisition for radiography. These outcomes will be assessed: 1 Measures of clinical impact will compare the changes from before to after between the intervention and control sites: a C-spine radiography ordering proportions the primary analysis; b Number of missed fractures; c Number of serious adverse outcomes; d Length of stay in ED; e Patient satisfaction. 2 Performance of the Canadian C-Spine Rule: a Accuracy of the rule; b Physician accuracy of interpretation; c Physician comfort and compliance. 3 Economic evaluation measures: a Radiography rate after discharge; b Length of stay in ED and hospital; c Hospital admission; d Operative repair. During the 12-month decay period, implementation strategies will continue, allowing us to evaluate the sustainability of the effect. We estimate a sample size of 4,800 patients in each period in order to have adequate power to evaluate the main outcomes. 