Chapter 19.4: Clinical Prediction Rules

CLINICAL SCENARIO

You are the medical director of a busy inner-city emergency department. Faced with a limited budget and pressure to improve efficiency, you have conducted an audit of radiologic procedures ordered for minor trauma and have found that the rate of radiographs ordered for ankle and knee trauma is high. You are aware of the Ottawa Ankle Rules, which help identify patients for whom it is safe to omit ankle radiographs without adverse consequences (Figure 19.4-1).^1,2 You are aware that only a small number of your institution's faculty and residents currently use the Ottawa Ankle Rules in the emergency department.

You are interested in knowing the accuracy of the Ottawa Ankle Rules, whether they are applicable to the population of patients in your hospital, and whether you should implement them in your own practice. Furthermore, you wonder whether implementing these rules can change clinical behavior and reduce costs without compromising quality of care. You decide to consult the original medical literature and assess the evidence for yourself.

To obtain a rapid overview of current best evidence that answers all of your questions, you start your search at the top of the pyramid of evidence-based medicine resources (see Chapter 5, Finding Current Best Evidence). You opt for the online summary in a preappraised-evidence resource, accessible through your institution. Using the term “ankle injury,” you quickly find a relevant chapter on “Decision Rules for Imaging of Ankle and Foot Injuries.” This chapter summarizes and provides detailed online references for the Ottawa clinical prediction rule for ankle fractures, its accuracy in ruling out ankle fractures, its validation in different populations and settings, and its impact when implemented in various emergency centers.

However, you are also interested in the first derivation article, which does not seem to be cited in the summary chapter. To rapidly find it, you go to PubMed, then Clinical Queries (http://www.ncbi.nlm.nih.gov/pubmed/clinical), and type “ankle Ottawa decision rules.” Under Clinical Study Categories, you choose the search filter “Clinical Prediction Guides” and choose as your scope “Broad” to find the derivation study. This retrieves 31 studies, of which the earliest one is the derivation study published in 1992.¹

In reviewing the articles you have found, you require criteria for deciding on the strength of the inference you can make about the accuracy and impact of the Ottawa Ankle Rules. This chapter provides the tools to answer those questions.