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Ottawa Ankle Rules OK

Bandolier 13 was taken by a Canadian newsletter which was the source of interesting evidence-based information. It described the Multicentre Ankle Rules Study which developed and tested a decision aid algorithm in Ontario.

The full results are now published in the BMJ [1], and interesting reading it is. The article describes a simple set of clinical decision rules used as an aid in deciding whether ankle or foot X-rays are needed. The rules are described in full in the BMJ article and are not rehearsed here, therefore.

The important issue was the way in which the rules (guidelines) were implemented to the benefit of patients and the healthcare system.

The study

All adult patients seen in eight hospitals in Ontario were studied during a control period of one year before and one year after the introduction of the rules. The control group had nearly 6,300 such patients and the intervention group nearly 6,500. The total population covered was not mentioned, but the individual hospitals included small community to large teaching establishments.

The Ottawa ankle rules were introduced by means of a lecture, handouts, pocket cards and posters in the emergency departments. The main outcome measures were the proportion of patients receiving X-rays and whether that was appropriate, the number of "missed" fractures, patient waiting times, and data on cost effectiveness.


The main result was a reduction in the proportion of patients given X-rays from 83% during the control year to 61% during the intervention year. These results were consistent across hospitals and doctors and most doctors used the rules correctly most of the time (over 95%).

So 1081 of 6288 patients with foot or ankle injuries did not have X-rays in the control period, compared with 2534 of 6489 patients in the intervention period. This is statistically significant with an odds ratio of 2.94 (95%CI 2.7 - 3.2).

The number-needed-to-treat (NNT) for the implementation of this intervention was 4.6 (95%CI 4.3 - 4.9). This means that the implementation of the Ottawa ankle rules saved one patient with ankle or foot injury from having an unnecessary X-ray for every five examined compared with not using the rules.

Missed fractures?

Nearly 2,200 patients without fracture in the intervention period were followed up at about 10 days by telephone call with a response of 94%. Three of 732 (0.4%) who had had an X-ray subsequently had a fracture diagnosed compared with seven of 1,301 (0.5%) who had not had an X-ray.

Benefits and cost-effectiveness

The patients without fracture spent on average 30 minutes less in the emergency department if they had no X-ray. The average cost differential between those who had and those who did not have an X-ray was $90 - about £50.


What makes the Ottawa ankle rules successful? Probably four things:-
  1. The rules were devised and tested with some rigour before they were more generally used.
  2. They had a sensitivity of 100%, or close to it. In layman's terms, they worked. This is an important issue, since many diagnostic and treatment decisions are made on the results of clinical, laboratory or other tests which have sensitivities and specificities far below 100%.
  3. They were simple and easy to remember, and so simple and easy to use.
  4. Their use produced a simple yes/no decision as to whether to X-ray the foot or ankle.

What are the implications of implementing the Ottawa ankle rules? Probably three things, but putting numerical estimates to them is difficult because the denominator of population was absent from the paper. However, in eight hospitals in one year it:

  1. Saved 1713 patients from having an X-ray.
  2. Saved 36 patient-days waiting in a hospital emergency room.
  3. Saved $154,000.

Divided between eight hospitals this may not seem much compared with the totality of their activity, but implementing many things that are simple, cheap and effective can make a big difference over time, especially when the driving force is benefit to patients. This is a splendid example of implementation in action.


1: I Stiell, G Wells, A Laupacis et al. Multicentre trial to introduce the Ottawa ankle rules for use of radiography in acute ankle injuries. British Medical Journal 1995 311: 594-7.

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