EBQ:Ottawa Ankle Rule Study
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Clinical Question
Can a clinical decision rule be used to aid in the efficient use of radiography in acute ankle injuries?
Conclusion
The Ottawa Ankle Rule is a highly sensitive decision rule used to determine the need for radiography in patients with acute ankle injuries.
Major Points
Ankle Rules
Ankle x-ray needed if pain near the maleoli AND
- Inability to bear weight immediately and in the ED (4 steps)
- OR
- Tenderness at posterior edge or tip of lateral malleolus
- OR
- Tenderness at posterior edge or tip of medial malleolus
Rule had 100% sensitivity and 49% specificity for identifying 50 clinically significant malleolar zone fractures in the prospective validation study.
Foot Rules
Foot x-ray series needed if pain in the midfoot AND
- Inability to bear weight both immediately and in the ED (4 steps)
- OR
- Tenderness at the navicular
- OR
- Tenderness at the base of the 5th metatarsal
Rule had 100% sensitivity and and 79% specificity for identifying 19 clinically significant midfoot fractures in the prospective validation study.
Study Design
- Conducted in 2 stages in 2 Canadian EDs
- Both prospective cohort studies
- In the first stage, each patient was evaluated for 15 clinical variables as defined by previously derived clinical decision rules. All patients then underwent radiographs--standard ankle series for patients with pain in malleolar zone vs. standard foot series for patients with pain in the midfoot zone.
- Original decision rule then refined by univariate and recursive partitioning analyses.
- In the second stage, each patient was evaluated for 6 clinical variables, and the decision rule was applied to determine necessity of radiographs.
- In both studies, a subset of patients were also assessed by second EM physician independently.
- Clinically significant fracture seen in ankle or foot radiographic series was the primary outcome, defined as bone fragments greater than 3 mm in breadth.
- All radiographic series were interpreted by qualified radiologists who were blinded to the data collection sheets.
Population
Patient Demographics
Similar characteristics in stage 1 (refinement) vs. stage 2 (validation)
- Mean age: 35 vs. 36
- Male gender: 52% vs. 52%
- Pt at Ottawa Clinic: 60% vs. 64%
- Twisting mechanism: 84% vs. 86%
- Clinically significant fractures: 16% vs. 15%
- Clinically insignificant fractures: 6% vs. 7%
- Ankle rediographs performed: 85% vs. 85%
- Foot radiographs performed: 39% vs. 35%
Inclusion Criteria
- Patients who presented to the emergency department with pain or tenderness 2/2 to blunt ankle trauma due to any mechanism of trauma
- Ankle defined as area commonly involved in twisting injuries
- Malleolar zone
- Distal 6 cm of tibia, fibula, talus
- Midfoot zone
- Navicular bone, cuboid, cuneiforms, anterior process of calcaneus, base of 5th metatarsal
- Malleolar zone
- 1 of 21 designated EM physicians had to be on duty
Exclusion Criteria
- Age <18 years old
- Pregnant
- Isolated injuries of the skin
- Referred from outside hospital with radiographs
- Injury occurred >10 days previously
- Returned for reassessment of the same injury
Interventions
Outcomes
First stage (validation and refinement of original rules): n=1032 enrolled and assessed
Second stage (validation of refined rules): n=453 enrolled and assessed
Primary Outcome
First stage (refinement): 121 (12%) clinically significant malleolar zone fractures and 49 (5%) clinically significant midfoot zone fractures identified
Performance of the Ottawa Decision Rule in the second stage (validation) cohort
| Ankle Decision Rule | Fracture | No Fracture |
|---|---|---|
| Rule Positive | 50 | 205 |
| Rule Negative | 0 | 198 |
Sensitivity 100% (95% CI 93% to 100%)
Specificity 49% (95% CI 44% to 54%)
| Foot Decision Rule | Fracture | No Fracture |
|---|---|---|
| Rule Positive | 19 | 90 |
| Rule Negative | 0 | 344 |
Sensitivity 100% (95% CI 83% to 100%)
Specificity 79% (95% CI 75% to 83%)
Secondary Outcomes
Stage 1 (refinement)
- Physicians correctly classified patients according to the ankle and foot decision rules in 97% and 98%
- Inter-observer agreement between physicians for ankle and foot decision rules was 56% and 69%
Stage 2 (validation)
- Physicians correctly classified patients according to the ankle and foot decision rules in 99% and 100%
- Potential reduction in radiography for ankle and foot series estimated to be 34% and 30%
- Likelihood ratio negative for a fracture estimated to be 0
Subgroup analysis
Criticisms & Further Discussion
- Rules may not be useful in patients with multiple painful injuries, altered sensorium, intoxication, paraplegia, or bone disease
- Limited experience with uncommon fractures
- 2 fractures of talus
- 12 fractures of midfoot other than base of 5th metatarsal
Funding
Grant from Emergency Health Services Branch of Ontario Ministry of Health, Toronto
Sources
- Stiell I, Wells G, Laupacis A, Brison R, Verbeek R, Vandemheen K, Naylor D. A multicentre trial to introduce clinical decision rules for the use of radiography in acute ankle injuries. British Medical Journal 1995; 311:594-597.