SGEM#3: To X-ray or not to X-ray (Ottawa Ankle Rule)

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Date: September 3, 2012

Case Scenario: An eight year old girl brought into emergency department by mother after twisting her ankle on a trampoline. She was able to walk on it but has become very swollen. The mother wants to know if she should get an xray to see if her daughter broke the ankle.

The Ottawa Ankle Rule (OAR): These were developed by Dr. Ian Stiell. He is one of the most famous Canadian emergency physicians.

The OAR represent one of the best known clinical decision instruments. The rule says xrays are only required if the patient is tender:

distal 6cm posterior edge of the tibia to the tip of the medial malleolus
distal 6cm posterior edge of the fibula to the tip of the lateral malleolus
base of the 5th metatarsal
navicular bone of the mid foot
or patient unable to weight bear immediately in the ED for 4 steps

(Does not apply to pregnant, drunk or head injured patients)

Dr. Stiell’s article on the OAR was published in the Ann Emerg Med 1992. There were 150 patients in the pilot stage and 750 in the main study. It showed the OAR was 100% sensitive and 40% specific. So it picked up all of the true positives or fractures. Applying the OAR would have decreased xrays by over one-third.

Question: Can the Ottawa Ankle Rule safely exclude ankle and foot fractures in children?

Reference: Dowling et al. Accuracy of Ottawa Ankle Rules to Exclude Fractures of the Ankle and Midfoot in Children: A Meta-analysis. Acad Emerg Med 2009

Population: 3,130 Children ≤18 yo presenting to the ED with blunt ankle and/or midfoot injury. The prevalence of fracture in this group was 21.4%.
Intervention: Application of the Ottawa Ankle Rule.
Control: None.
Outcome: Any fracture of the ankle or midfoot using an x-ray or a proxy measure (phone follow up) as the criterion standard.

Authors’ Conclusions: “The OAR appear to be a reliable tool to exclude fractures in children greater than 5 years of age presenting with ankle and/or midfoot injuries. Employing the OAR would significantly decrease x-ray use with a low likelihood of missing a fracture.”

BEEM Commentary: The OAR have been well validated in the adult population but its use in children has remained unclear. Children pose special challenges in the application of this clinical decision instrument due to various age related issues (ability to ambulate, difficulty in assessing pain, presence of growth plates). The authors of the SR rigorously test this decision instrument in children and appropriately conclude that it can be safely applied in children aged five and older. Only 10 fractures were missed in the pooled analysis of 3,130 children. 4 of these 10 were described of which 2 were deemed insignificant (SH-I or avulsion fracture <3mm). If these were excluded, the decision instrument would have even better performance characteristics than the authors’ conservative measures.