What are the criteria for applying the Ottawa knee rule to determine if a patient with a knee injury requires an X-ray?

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 after the injury, or inability to walk four steps in the emergency room. 1

Detailed Criteria Explanation

The Ottawa Knee Rule consists of six specific criteria that require knee radiography when any one is present:

1. Age ≥ 55 years

   • Radiographs indicated regardless of other findings due to higher fracture risk in older adults

2. Palpable tenderness over the head of the fibula

   • Specific palpation of the fibular head that elicits pain

3. Isolated patellar tenderness

   • Pain specifically localized to the patella during examination

4. Inability to flex the knee to 90 degrees

   • Patient cannot bend the knee to a right angle during examination

5. Inability to bear weight immediately after injury

   • Patient could not stand on the affected leg right after the injury occurred

6. Inability to walk four steps in the emergency room

   • Patient cannot take four consecutive steps (both bearing weight and transferring weight) during evaluation

Clinical Application and Effectiveness

The Ottawa Knee Rule has been extensively validated with:

• 100% sensitivity for detecting knee fractures in multiple studies 2
• Potential to reduce radiography use by 26-49% 3, 2
• High interobserver reliability (kappa = 0.91) 3

Important Exceptions and Limitations

The Ottawa Knee Rule should NOT be applied in patients with:

• Gross deformity
• Palpable mass
• Penetrating injury
• Prosthetic hardware
• Unreliable clinical history due to multiple injuries
• Altered mental status (head injury, drug/alcohol use, dementia)
• Neuropathy (paraplegia, diabetes)
• History suggesting increased fracture risk 1

Age Considerations

• The Ottawa Knee Rule applies to patients ≥18 years
• For patients <18 years, some studies suggest the rule may be applicable, but it was not originally validated in this population 4
• For patients between 5-12 years, radiographs may be beneficial despite lack of clinical symptoms as they fall outside both the Ottawa and Pittsburgh rule criteria 1

Alternative: Pittsburgh Decision Rule

The Pittsburgh Decision Rule is an alternative that recommends radiographs for:

• Patients <12 years old or >50 years old
• Patients who cannot take four weight-bearing steps in the emergency department 1

Clinical Impact

Implementation of the Ottawa Knee Rule has been shown to:

• Reduce emergency department wait times (85.7 vs 118.8 minutes)
• Lower healthcare costs ($80 vs $183 per patient)
• Maintain patient safety with no missed fractures 3

By applying these criteria systematically, clinicians can effectively determine which patients with knee injuries require radiographic evaluation while avoiding unnecessary imaging.