Applies to adults (generally ≥18 years) presenting within about 7 days of blunt knee trauma in emergency, urgent care or general practice. It is designed to identify which patients need knee radiographs to exclude clinically important fractures.

Evidence and performance

Study	Population / setting	Key findings
Derivation (Stiell 1995)	1,047 adults with acute knee injuries in two Ottawa emergency departments	Five clinical criteria (age ≥55 years, isolated patellar tenderness, fibular head tenderness, inability to flex to 90°, inability to bear weight for 4 steps) identified all 68 knee fractures with 100% sensitivity and 54% specificity, and would have reduced radiography use by 28% (from 68.6% to 49.4%).
Systematic review (Bachmann 2004)	Six adult studies, 4,249 patients	Pooled sensitivity 98.5%, specificity 48.6% and negative likelihood ratio 0.05, implying a very low (<~1–2%) probability of fracture after a negative rule in typical emergency populations.
Meta-analysis (Sims 2020)	Eight adult studies, 7,385 patients	Sensitivity 0.99 and specificity 0.49 with negative likelihood ratio 0.07, supporting use of the rule to safely reduce knee radiographs, waiting times and imaging costs.

Paediatric validation studies show mixed results and higher residual fracture risk after a negative rule, so most authors advise against using it in patients under 18 years.

The rule should not be applied when examination is unreliable (eg reduced consciousness, intoxication, communication barriers), in multiple trauma, open fractures, gross deformity or isolated superficial soft-tissue injuries. It targets clinically important fractures only. it does not exclude ligament, meniscal or other internal derangements, so persistent mechanical symptoms still warrant review and further imaging if indicated.

Implementation and guideline reviews, including Australian primary care work, suggest that appropriate use can substantially reduce knee radiography without increasing missed clinically important fractures, provided patients have clear follow-up and return advice.

Ottawa Knee Rule