Is the Ottawa Knee Rule (OKR) valid for use in pediatric patients?

Validity of the Ottawa Knee Rule in Children

The Ottawa Knee Rule (OKR) is valid and effective for children over 5 years of age, with high sensitivity (99%) for detecting knee fractures, though it should not be used in children under 5 years of age. 1

What is the Ottawa Knee Rule?

The Ottawa Knee Rule recommends knee radiographs for patients with acute knee injury if any of the following criteria are present:

• Age 55 years or older
• Isolated tenderness of the patella
• Tenderness at the head of the fibula
• Inability to flex the knee to 90 degrees
• Inability to bear weight for four steps both immediately after the injury and in the emergency department

Evidence for OKR in Children

Sensitivity and Specificity

• A systematic review and meta-analysis found the OKR has a pooled sensitivity of 99% (CI 94.4% to 99.8%) and specificity of 46% (CI 43.0% to 49.1%) in children over 5 years of age 1
• A multicenter validation study of 750 children (ages 2-16) showed 100% sensitivity (95% CI 94.9% to 100%) with a specificity of 42.8% (95% CI 39.1% to 46.5%) 2

Potential for Reducing Radiographs

• Application of the OKR could reduce radiography by 30-40% in pediatric populations 1
• One study demonstrated a potential 31.2% absolute reduction in radiographs if the OKR had been strictly applied 2

Important Considerations and Limitations

Age Restrictions

• The OKR should only be applied to children over 5 years of age 3, 1
• There is insufficient evidence to support using the OKR in children under 5 years 1

Exclusionary Criteria

Similar to the Ottawa Ankle Rules, the OKR should not be used or should be used with caution in the following scenarios 3:

• Penetrating trauma
• Pregnancy
• Skin wounds
• Patients transferred with radiographs already taken
• Injuries >10 days old
• Return visits for continued traumatic pain
• Polytrauma
• Altered sensorium
• Neurologic abnormalities affecting the extremity
• Underlying bone disease

Missed Fractures

• One study reported a missed non-displaced proximal tibial fracture in an 8-year-old when applying the OKR (sensitivity 92%) 4
• This highlights the importance of clinical judgment even when applying validated decision rules

Clinical Application

1. Assess for exclusionary criteria first to determine if the OKR can be safely applied
2. Verify the child's age is over 5 years
3. Apply the OKR criteria systematically
4. Order radiographs if any criteria are positive
5. Consider radiographs regardless of OKR results if clinical suspicion remains high

Common Pitfalls to Avoid

• Applying the rule to children under 5 years - evidence doesn't support this practice
• Using the rule when exclusionary criteria are present - this may lead to missed fractures
• Relying solely on the rule without clinical judgment - the rule is a tool to aid decision-making, not replace it
• Failing to recognize growth plate injuries - children have unique fracture patterns that may be subtle

The OKR remains a valuable clinical decision tool that, when properly applied to the appropriate pediatric population, can effectively reduce unnecessary radiographs while maintaining high sensitivity for detecting clinically significant fractures.