Ottawa Ankle Rules

This is part of a recurring series examining landmark articles in Emergency Medicine, in the style of ALiEM’s 52 Articles.

Discussing:  Stiell IG, et al. Decision Rules for the Use of Radiography in Acute Ankle Injuries. JAMA 1993; 269 (9): 1127 – 1132.

 X-Rays for ankle fractures? Is trouble a foot?

With a such a refined Canadian tool you can’t act like a fool.

 The Rules:

Ottawa Ankle

Main Points:

  1. The Ottawa ankle rule is an excellent screening tool for patients with ankle and foot injuries. In this study, it was found to have a sensitivity of 100 percent and is therefore unlikely to miss clinically significant ankle and midfoot injuries.
  2. These simple rules allowed physicians to safely reduce the number of radiographs ordered in patients with ankle and foot injuries by nearly a third.
  3. Based on the combined 1485 patients seen in the two stages the negative likelihood ratio for a fracture is estimated to be 0 for both the ankle and foot series rules!

Background:

Acute ankle injuries are one of the most common presenting complaints seen in the Emergency Department. Ankle radiographs are typically the second most commonly performed musculoskeletal examination, after the cervical spine. It was estimated that more than 5 million ankle radiographs are ordered annually in Canada and the USA with a cost of $500 creating a massive burden on the healthcare systems. Out of all of these images, treatable fractures are present in less than 15 percent of cases.

In 1992, Ian Stiell and his colleagues derived a clinical decision tool for the use of radiography in acute ankle and foot injuries. In the original study, thirty-two clinical variables were assessed for association with fractures seen on x-ray. Using these results, a set of rules were derived to determine if imaging was necessary for patients with ankle and foot injuries who met certain criteria. The goal of the study being reviewed here was to prospectively validate and potentially refine the decision rules to have the highest sensitivity possible, 100 percent, for identifying malleoli and midfoot fractures.

Methods:

The study was set up as a convenience survey and was prospectively administered in two stages: validation and refinement of the original rules, followed by validation of the refined rules in a new group of patients. For the study, injuries were subdivided into malleolar and midfoot zones. Patients who presented to the emergency department with pain or tenderness secondary to blunt ankle trauma due to any mechanism of injury were included. Patients were excluded if they were less than 18 years old, pregnant, has isolated skin injuries, were referred from outside facility with X-rays already completed, if injuries occurred more than 10 days ago, or if the patient had returned for reassessment of the injury.

Participants were evaluated by emergency medicine physicians who recorded their findings and interpretation of the decision rules on a standardized data collection sheet. All patients were then referred for radiography. Images were interpreted by radiologists who were blinded to the findings of the physician in the ED. Clinically significant fractures were defined as bone fragments greater than 3 mm in breadth, as avulsion fractures of 3 mm or less are not treated with plaster immobilization in the institutions involved in the study.

Data collected from the first stage was analyzed in order to refine the decision rules towards the objective of a sensitivity of 1.0. Each of the clinical variables were assessed for association with significant fractures in the ankle and foot radiographs. In the second stage, the sensitivity and specificity of the refined decision rules (see image above) was calculated and the accuracy and reliability of the physicians’ interpretation of the rules was determined.

 Main Results:

  • In stage I, the original decision rules were found to have sensitivities of 1.0 (95% CI 0.97 to 1.0) for detecting ankle fractures, and 0.98 (95% CI, 0.88 to 1.0) for detecting midfoot fractures.
  • In stage II, the refined rules proved to have sensitivities of 1.0 (95% CI, 0.93 to 1.0) for ankle fractures, and 1.0 (95% CI, 0.83 to 1.0) for midfoot fractures.
  • When the decision rules are used to rule out a patient for significant fractures, the probability of fractures were estimated to be 0% (95% CI, 0% to 0.8%) in the ankle series, and 0% (95% CI, 0% to 0.4%) in the foot series.
  • Using the Ottawa ankle rules, X-ray imaging can be reduced 34% for the ankle series and 30% for the foot series.

Commentary:

Since the publication of this study, the Ottawa ankle rule have been well validated and have been shown to limit the number of radiographs obtained for ankle injuries, decreased patient wait times and cost. These decision rules allow physicians to use clinical judgment to screen for acute ankle and foot injuries, rather than relying on X-rays. Although convenient, the Ottawa ankle rules cannot be applied to all patients. The decision rules do not apply to patients with multiple painful injuries, altered mental status, intoxication, bone diseases, or paraplegia.

There continues to be some reluctance to use the Ottawa ankle rules due to the ease and speed of obtaining radiographs, patient expectations, and fears of missed fractures and possible litigation. Documenting your physical examination and arranging for follow-up in patients whose pain and ability to ambulate have not improved after several days protects both the patient and the physician from the consequences of missing a fracture.

Related Articles:

Stiell IG, McKnight RD, Greenberg GH, et al. Interobserver Agreement in the Examination of Acute Ankle Injury Patients. Am J Emerg Med, 1992; 10:14-17.

Stiell IG, Greenberg GH, McKnight RD, et al. A study to develop clinical decision rules for the use of radiography in acute ankle injuries. Ann Emerg Med. 1992 April; 21:384-90.

Stiell IG, McKnight RD, Greenberg GH, et al. Implementation of the Ottawa Ankle Rules. JAMA, 1994; 271:827-832.

Stiell IG, Wells G, Laupacis A, et al. Multicenter Trial to Introduce the Ottawa Ankle Rules for Use of Radiography in Acute Ankle Injuries. BMJ, 1995; 311:594-597.

Bachmann LM, Kolb E, Koller MT. et al. Accuracy of Ottawa ankle rules to exclude fractures of the ankle and mid-foot: systematic review. BMJ. 2003 Feb 22;326(7386):417.

Level of Evidence:

Based on the ACEP grading system this study was graded level I

Surprises:

  • Variables that were shown to not be useful in the original study included: mechanism of injury, “cracking” sound, ecchymosis, range of motion, drawer sign, soft-tissue tenderness and proximal fibular tenderness.
  • Weight bearing is defined as four steps, the ability to transfer weight twice onto each leg, regardless of limping. Assess ability to bear weight after determining bony tenderness
  • One drawback to the Ottawa rules is the fairly low specificity, which generally is around 30 to 40 percent.
  • The study population included patients aged 18-92. Not imaging the geriatric patient, is that a decision you feel comfortable with?

Resident Reviewer: Dr. Kazakin
Faculty Reviewer: Dr. Siket

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