Emergency and critical care
Ottawa ankle and knee rules
The Ottawa rules decide whether an X-ray is needed after an ankle, midfoot or knee injury. They are highly sensitive for clinically significant fracture, which is what makes a negative result safe to act on.
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This calculator is provided for reference and education. It does not replace clinical assessment, examination, current guidelines, local protocol, or professional judgment. Verify every result before acting on it. Nirogix accepts no liability for clinical decisions made using this tool.
The formula
- Ankle and midfoot: pain in the region plus any of malleolar bone tenderness, navicular tenderness, fifth metatarsal base tenderness, or inability to bear weight for four steps.
- Knee: any of age 55 or over, fibular head tenderness, isolated patellar tenderness, inability to flex to 90°, or inability to bear weight for four steps.
When to use it
- Acute ankle, midfoot or knee injury in an alert, cooperative adult
And when not to
- Not for children under 5, intoxicated patients, those with distracting injuries or reduced sensation, or injuries more than ten days old.
- It is a rule for clinically significant fractures. It will miss some avulsion fragments that would not have changed management.
References
- Decision rules for the use of radiography in acute ankle injuries — Stiell IG et al., JAMA, 1993
- Prospective validation of a decision rule for the use of radiography in acute knee injuries — Stiell IG et al., JAMA, 1996
Last reviewed 07/09/2026.
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