Ottawa Knee Rule

What is the Ottawa Knee Rule?

The Ottawa Knee Rule is a clinical decision rule developed to help clinicians determine which patients with acute knee injuries require radiographic evaluation (X-rays). It was developed by Dr. Ian Stiell and colleagues at the University of Ottawa to reduce unnecessary radiography without missing clinically significant fractures.

This evidence-based tool has been extensively validated and has demonstrated high sensitivity (98-100%) for detecting clinically significant knee fractures while potentially reducing the number of unnecessary X-rays by 20-30%.

Clinical Application

The Ottawa Knee Rule applies to patients with:

• Acute knee injury (within 7 days)
• Age 18 years or older (though some studies have validated its use in pediatric populations)

According to the rule, a knee X-ray is only required if any of the following criteria are present:

• Age 55 years or older
• Isolated tenderness of the patella (no bone tenderness of the knee other than the patella)
• Tenderness at the head of the fibula
• Inability to flex the knee to 90 degrees
• Inability to bear weight both immediately after the injury and in the emergency department (four steps; unable to transfer weight twice onto each lower limb regardless of limping)

Benefits and Impact

Implementation of the Ottawa Knee Rule offers several benefits:

• Reduction in unnecessary radiography by approximately 20-30%
• Decreased emergency department wait times
• Reduced healthcare costs
• Decreased radiation exposure for patients
• Standardized approach to knee injury assessment

Studies have shown that proper implementation of the Ottawa Knee Rule can lead to significant cost savings without compromising patient care or missing clinically important fractures.

Limitations and Considerations

While the Ottawa Knee Rule is a valuable tool, it has several limitations:

• It is not applicable to patients with:
  • Isolated skin injuries
  • Injuries more than 7 days old
  • Repeat presentations for the same injury
  • Pregnancy
  • Paraplegia or multiple injuries
• It does not assess for ligamentous or meniscal injuries, which may require different diagnostic approaches
• Clinical judgment should always be used alongside the rule
• The rule has high sensitivity but lower specificity, meaning it will identify most fractures but may still lead to some unnecessary X-rays

Proper Examination Technique

To properly apply the Ottawa Knee Rule, clinicians should:

1. Determine the patient's age
2. Assess for isolated patellar tenderness by palpating the patella directly
3. Palpate the head of the fibula for tenderness
4. Assess knee flexion, asking the patient to bend the knee to 90 degrees
5. Assess weight-bearing ability by asking the patient to take four steps (two on each leg), even if limping

It's important to note that the rule is designed to be applied sequentially. If any criterion is positive, an X-ray is indicated, and the remaining criteria do not need to be assessed.

References

1. Stiell IG, Greenberg GH, Wells GA, et al. Derivation of a decision rule for the use of radiography in acute knee injuries. Ann Emerg Med. 1995;26(4):405-413.
2. 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;278(23):2075-2079.
3. Bachmann LM, Haberzeth S, Steurer J, ter Riet G. The accuracy of the Ottawa knee rule to rule out knee fractures: a systematic review. Ann Intern Med. 2004;140(2):121-124.
4. Bulloch B, Neto G, Plint A, et al. Validation of the Ottawa Knee Rule in children: a multicenter study. Ann Emerg Med. 2003;42(1):48-55.
5. Beutel BG, Trehan SK, Shalvoy RM, Mello MJ. The Ottawa knee rule: examining use in an academic emergency department. West J Emerg Med. 2012;13(4):366-372.