Trauma & Burns

Ottawa Knee Rule Calculator

Decides whether an adult with an acute knee injury needs a knee X-ray series.

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · From the Reference tab of the app

Turn on JavaScript to use this calculator, or open it in the web app.

Formula

Knee X-ray series if any one of:
Age 55 or older
Tenderness at the head of the fibula
Isolated tenderness of the patella
Unable to flex to 90°
Unable to bear weight for 4 steps both immediately and in the emergency department

How it is used

• Derived in 1,047 adults: any one finding identified all 68 fractures (sensitivity 1.0, specificity 0.54) and would have cut knee radiography by 28% (Stiell 1995).
• Validated prospectively in 1,096 adults: sensitivity 1.0 for 63 clinically important fractures, probability of fracture with a negative rule 0% (95% CI 0–0.4%), 28% fewer radiographs (Stiell 1996).
• Built for adults with acute knee injuries; it was not derived in children.

Key points

• A negative rule rules out a fracture, not a ligament or meniscal injury.

Same formula as the app. Open it in the web app.

Related one-pagers

• Burns
• Trauma: Primary and Secondary Survey

Related calculators

• Burn Fluids (ABA Consensus 2 mL/kg)
• Burn Size (Rule of Nines)
• Canadian CT Head Rule (CCHR)
• NEXUS Cervical Spine Criteria (NEXUS)
• Ottawa Ankle and Foot Rules

For education and exam preparation only. Follow your institution’s protocols. For education and exam preparation only. Verify results independently and follow your institution’s protocols. Not a substitute for clinical judgment.