The Ottawa Knee Rule is a simple guideline developed to aid emergency physicians in deciding when to use radiography for patients with injuries to the knee. Prospective validation of the Ottawa Knee Rule has shown this decision rule to be 100% sensitive for identifying fractures of the knee, to be reliable and acceptable, and to have the potential to allow physicians to reduce the use of radiography in patients with acute knee injury.

A knee x-ray is only required for knee injury patients with any of these findings:

• age 55 or over
• 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 to 90 degrees
• inability to weight bear both immediately and in the casualty department (4 steps - unable to transfer weight twice onto each lower limb regardless of limping).

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