An economic analysis of the ottawa knee rule. 
To conduct an economic analysis of the implementation of the Ottawa Knee Rule.  The decision analysis compared usual practice based on physician judgment with practice based on a clinical decision rule, which allows more selective use of radiography.  The study participants were all adults with blunt knee trauma.  The likelihood and cost of radiography, missed fracture, lost productivity, and medicolegal actions were defined by published data and an expert panel.  Separate analyses considered US Medicare and Canadian hospital costs.  Sensitivity analyses considered a range of values for each variable in the model, including costs in a US fee-for-service setting.  The study out-come was the mean cost per patient.  The mean cost savings associated with practice based on the Ottawa Knee Rule was $31 (95% confidence interval 22 to 44) to $34 (95% confidence interval 24 to 47) per patient.  These results were robust to reasonable changes in the values of variables in the model.  Implementation of the Ottawa Knee Rule Would be associated with meaningful reductions in societal health care costs both in the United States and Canada without a reduction in quality of care.