Clinical decision rule
Ottawa Knee Rule
The Ottawa Knee Rule determines whether an acute knee injury requires radiographs using five criteria — age 55 or over, isolated patellar tenderness, fibular head tenderness, inability to flex to 90 degrees, and inability to bear weight for four steps — and is close to 99% sensitive for clinically significant fractures.
What the Ottawa Knee Rule means
Ottawa Knee Rule scores run from 0 to 1, where a lower score is better. The bands below are conventional reporting categories, not diagnostic cut-offs.
- Imaging not indicated0–0
- Imaging indicated1–1
Published criteria and reliability
The published cut-offs that define this instrument, and the measured agreement between observers using it. Each is reported with the population it was derived in.
| Type | Value | Subscale | Population | Follow-up | Source |
|---|---|---|---|---|---|
| Criterion | Sensitivity 98–99%, specificity 46–49% | — | Adults with acute blunt knee trauma | — | Bachmann LM 2004 |
| Criterion | Reduces knee radiography use by approximately 20–30% | — | Emergency department | — | Stiell IG 1997 |
| Criterion | Pooled sensitivity 99% in children over 5 years | — | Paediatric acute knee injury | — | Bachmann LM 2004 |
Criterion is a published cut-off, definition or performance figure belonging to a classification or decision rule — it is not a change score and should not be read as one.
How the score is calculated
Stated in full so the calculation can be independently checked, and reproduced by hand if needed.
The five criteria are assessed independently and any single positive criterion indicates a knee radiograph series. The rule is designed as a rule-out tool: its value lies in confidently excluding fracture when all five criteria are negative, not in predicting fracture when one is positive.
Instrument profile
- Developer
- Ian Stiell and colleagues
- Institution
- University of Ottawa, Canada
- First published
- 1995
- Items
- 5
- Response format
- Yes/No criteria
- Score range
- 0 to 1
- Direction
- Lower score = better
- Completion time
- About 1 minutes
- Age range
- Adults 18 and over; validated in children from age 2 in some series
- Regions
- Knee
- Conditions
- Acute knee injury, Knee trauma, Patellar fracture, Tibial plateau fracture
- Validity
- Pooled sensitivity of 98.5% across validation studies, with a negative likelihood ratio of approximately 0.05.
- Reliability
- Specificity is deliberately low. The rule is built to exclude fracture safely rather than to identify it, so a positive result is an indication to image rather than a prediction of fracture.
When to use the Ottawa Knee Rule
Well suited to
- Acute blunt knee trauma within 7 days in an alert, cooperative patient.
- Emergency and urgent care settings where reducing unnecessary radiography is a goal.
Limitations and poor fits
- Intoxicated or uncooperative patients, or those with distracting painful injuries.
- Diminished sensation in the leg, or a knee that cannot be examined because of swelling or guarding.
- Injuries more than 7 days old, re-presentations, and patients who already have radiographs.
- Penetrating trauma, or isolated superficial injuries without a mechanism of blunt force.
Ottawa Knee Rule compared with other instruments
Instruments measuring a related construct, with the practical difference between them.
| Instrument | Items | Range | What it adds |
|---|---|---|---|
| Ottawa Ankle Rules | 7 | 0–1 | The Ottawa Ankle Rules determine whether an acute ankle or midfoot injury requires radiographs, based on bone tenderness at four specific sites and the ability to bear weight for four steps; they are approximately 98% sensitive for clinically significant fractures. |
| Pittsburgh Knee Rules | 3 | 0–1 | The Pittsburgh Knee Rules indicate a knee radiograph after blunt trauma or a fall when the patient is younger than 12 or older than 50, or cannot walk four weight-bearing steps in the emergency department — and the rule does not apply at all to any other mechanism of injury. |
Copyright and permitted use
Published openly because it is the question every clinician and researcher asks before using an instrument, and almost nobody answers it.
The Ottawa Knee Rule is a published clinical decision rule. The criteria are freely reproducible and no licence is required.
References
- Stiell IG, Greenberg GH, Wells GA, et al.. Derivation of a decision rule for the use of radiography in acute knee injuries. Annals of Emergency Medicine. 1995.PMID 7574127
- Stiell IG, Wells GA, Hoag RH, et al.. Implementation of the Ottawa Knee Rule for the use of radiography in acute knee injuries. JAMA. 1997.PMID 9366577
- Bachmann LM, Haberzeth S, Steurer J, ter Riet G. The accuracy of the Ottawa knee rule to rule out knee fractures: a systematic review. Annals of Internal Medicine. 2004.PMID 15096333
Editorial status
This page has not yet been signed off by a named clinical reviewer. The scoring logic is stated in full above so it can be independently verified, and every threshold is traceable to its source. See our editorial methodology.