Ottawa Knee Rule Criteria for Radiography in Acute Knee Injury
According to the Ottawa Knee Rule, palpable tenderness over the head of the fibula is one of the key factors that warrants radiography in a patient with an acute knee injury. 1
Ottawa Knee Rule Criteria
The Ottawa Knee Rule states that patients 18 years of age or older with acute knee pain should have knee radiographs if they meet ANY of the following criteria:
- Age 55 years or older
- Palpable tenderness over the head of the fibula
- Isolated patellar tenderness
- Inability to flex the knee to 90°
- Inability to bear weight immediately following the injury
- Inability to walk in the emergency room (after taking 4 steps)
Evidence Supporting the Ottawa Knee Rule
The Ottawa Knee Rule has been extensively validated and demonstrates excellent sensitivity for detecting knee fractures:
- Multiple studies confirm nearly 100% sensitivity for fracture detection 1, 2, 3
- A 2020 study found 100% sensitivity with 39% specificity 2
- A 2001 multicenter study demonstrated 100% sensitivity (95% CI 96-100%) 3
- Implementation can reduce unnecessary radiographs by approximately 35-49% 1, 3
Clinical Application
When examining a patient with acute knee injury:
- Assess for all six Ottawa Knee Rule criteria
- Order knee radiographs if ANY single criterion is present
- If no criteria are present, radiographs can safely be avoided
Potential Pitfalls and Caveats
- The rule applies specifically to patients 18 years and older 1
- For patients under 18, different criteria may apply (Pittsburgh Decision Rule covers ages 3-18) 1
- The rule should not be applied in cases with gross deformity, palpable mass, or penetrating injury 1
- While highly sensitive, the rule has relatively low specificity (19-44%) 2, 4, 5
- One study reported a fracture missed by the Ottawa Rule, but it was only detectable by MRI 1
Comparative Decision Rules
The Pittsburgh Decision Rule is an alternative approach that focuses on:
- Age (<12 or >50 years)
- Inability to take four weight-bearing steps in the emergency department
Some studies suggest the Pittsburgh rule may be more specific without losing sensitivity 6, but the Ottawa Knee Rule remains more widely implemented and validated.