🦵 Ottawa Knee Rule
Decide whether a knee X-ray is needed after acute injury with the Ottawa Knee Rule.
Clinical takeaway
Highly sensitive for clinically significant fractures.
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When to use
Reduce unnecessary knee radiography in the ED.
How it works
X-ray if any: age ≥ 55, isolated patellar tenderness, fibular head tenderness, inability to flex to 90°, or inability to bear weight 4 steps.
Key points
- Highly sensitive for clinically significant fractures.
- Apply to alert adults with acute isolated injury.
- Inability to bear weight = both immediately and in the ED.
References
Decision support for licensed clinicians only; not a substitute for clinical judgement, diagnosis or local protocols.
Worked calculation
The values below come from this tool's own example placeholders and are computed server-side with the formula shown on this page, so the arithmetic can be checked quickly. It demonstrates how to substitute values only — it is not clinical advice and not a real case.
| Age ≥ 55 | No |
|---|---|
| Isolated tenderness of the patella | No |
| Tenderness at the head of the fibula | No |
| Unable to flex to 90° | No |
| Unable to bear weight 4 steps (then & now) | No (can) |
→Knee X-rayNot indicated
- Rule：X-ray if any of: age ≥ 55, isolated patellar tenderness, fibular head tenderness, can't flex 90°, can't bear weight 4 steps.
| Age ≥ 55 | Yes |
|---|---|
| Isolated tenderness of the patella | Yes |
| Tenderness at the head of the fibula | Yes |
| Unable to flex to 90° | Yes |
| Unable to bear weight 4 steps (then & now) | Yes (cannot) |
→Knee X-rayIndicated
- Rule：X-ray if any of: age ≥ 55, isolated patellar tenderness, fibular head tenderness, can't flex 90°, can't bear weight 4 steps.
Frequently asked questions
- What is Ottawa Knee Rule?
- Decide whether a knee X-ray is needed after acute injury with the Ottawa Knee Rule.
- How is Ottawa Knee Rule calculated? What is the core formula?
- X-ray if any: age ≥ 55, isolated patellar tenderness, fibular head tenderness, inability to flex to 90°, or inability to bear weight 4 steps.
- When is Ottawa Knee Rule used?
- Reduce unnecessary knee radiography in the ED.
- What are the key clinical points for Ottawa Knee Rule?
- Highly sensitive for clinically significant fractures. Apply to alert adults with acute isolated injury. Inability to bear weight = both immediately and in the ED.
- What are the limits and cautions when using Ottawa Knee Rule?
- For licensed clinicians and clinical researchers. Interpret results with history, investigations and local protocols; not a diagnosis or prescription, and not a substitute for multidisciplinary decision-making or local guidelines.
- How is Ottawa Knee Rule calculated in practice? Can you show a worked example?
- Inputs: Age ≥ 55 No, Isolated tenderness of the patella No, Tenderness at the head of the fibula No, Unable to flex to 90° No, Unable to bear weight 4 steps (then & now) No (can) → Result: Knee X-ray Not indicated（Rule: X-ray if any of: age ≥ 55, isolated patellar tenderness, fibular head tenderness, can't flex 90°, can't bear weight 4 steps.） Inputs: Age ≥ 55 Yes, Isolated tenderness of the patella Yes, Tenderness at the head of the fibula Yes, Unable to flex to 90° Yes, Unable to bear weight 4 steps (then & now) Yes (cannot) → Result: Knee X-ray Indicated（Rule: X-ray if any of: age ≥ 55, isolated patellar tenderness, fibular head tenderness, can't flex 90°, can't bear weight 4 steps.）