Ottawa Knee Rules

The Ottawa Knee Rule is a validated clinical decision tool developed by Dr. Ian Stiell and colleagues to determine which patients with acute knee injuries require radiographic imaging. First published in 1995 and subsequently validated in multiple large multicenter studies, the rule has become a standard of care in emergency departments worldwide.

Knee injuries are the second most common extremity injury seen in emergency departments after ankle injuries. Before the Ottawa Knee Rule was introduced, approximately 70-80% of patients with knee injuries received radiographs, yet only about 6-7% of these X-rays revealed clinically significant fractures. This represented substantial overuse of radiographic imaging, with associated costs, patient inconvenience, and radiation exposure.

The Ottawa Knee Rule uses five simple clinical criteria that can be assessed rapidly at the bedside: age 55 or older, isolated patellar tenderness, fibular head tenderness, inability to flex the knee to 90 degrees, and inability to bear weight for four steps. If none of these criteria are present, knee radiography is not recommended. Implementation of this rule reduces X-ray utilization by approximately 28-32% without missing clinically significant fractures.

The rule demonstrates excellent diagnostic performance with a sensitivity of 97-100% for clinically significant knee fractures. The specificity is approximately 49%, meaning some patients without fractures will still undergo imaging. However, the high sensitivity ensures patient safety, and the reduction in imaging compared to universal radiography is substantial and cost-effective.

The Ottawa Knee Rule should be applied only to patients over age 18 with acute knee injury. It should not be used in patients with altered mental status, intoxication, distracting injuries, diminished sensation, obvious deformity suggesting fracture or dislocation, or injuries more than 7 days old. Pediatric patients require separate assessment criteria.

The rule has been endorsed by the American College of Emergency Physicians, the Canadian Association of Emergency Physicians, and numerous orthopedic societies. Studies have shown that consistent application of the Ottawa Knee Rule saves healthcare systems millions of dollars annually while maintaining excellent patient outcomes and satisfaction.