The Ottawa knee rule was developed to provide guidelines for the radiographic assessment of acute knee injuries (see the accompanying table). Implementation of the Ottawa knee rule has been shown to have the potential of decreasing the use of knee radiographs by 28 percent. Stiell and colleagues conducted a controlled clinical trial to assess the application of the Ottawa knee rule in clinical settings and its impact on the evaluation of acute knee injuries.

The study included over 3,000 adults who underwent treatment for acute knee injury at one of four hospitals. At two of the hospitals, physicians received a brief lecture about the Ottawa knee rule and a pocket guide for reference. In addition, posters of the Ottawa knee rule were displayed in the emergency department. Physicians were encouraged to use the Ottawa knee rule when deciding whether to order radiographs in patients with acute knee injuries. The other two hospitals served as control sites, and physicians at these hospitals did not receive instructions on the Ottawa knee rule.

After the Ottawa knee rule was emphasized in the two intervention hospitals, there was a relative reduction of 26.4 percent in the proportion of patients referred for knee radiographs, compared with a 1.3 percent relative reduction at the two control sites. The Ottawa knee rule was interpreted accurately by the physicians 97.7 percent of the time at the intervention hospitals.

In 3.5 percent of cases, radiographs were ordered even though adherence to the knee rule would not have led to a decision to obtain radiographs. None of these patients had fractures. Reasons for not following the Ottawa knee rule in these patients included the physician's disagreement with the rule, the patient's or orthopedic consultant's insistence on radiographs and unreliable physical examination because the patient was intoxicated.

The Ottawa knee rule was found to have a sensitivity of 1.0 and a negative predictive value of 1.0 by correctly identifying all 58 of the clinically important fractures in the study population. Nearly all of the patients (98.7 percent of those undergoing radiography and 95.7 percent of those who did not have radiographic examinations) were satisfied with the care they received for their knee injuries. Patients who were discharged without undergoing radiography had shorter stays in the emergency department (85.7 minutes versus 118.8 minutes) and incurred lower costs ($80 versus $183).

The authors conclude that the Ottawa knee rule can reduce the use of knee radiographs without compromising patient satisfaction and patient care.