Background This study was designed to determine the accuracy of the Ottawa Knee Rule (OKR) when applied to patients with acute knee injury in the Iranian population of the Imam Hospital Emergency Department (ED) at.

Methods This prospective cohort validation study included a convenience sample of all patients with a blunt knee injury sustained in the preceding 7 days presenting to the ED of a tertiary care teaching hospital during the study period. Patients were assessed for the five variables comprising the OKR, and a standardised data form was completed for each patient. Standard knee radiographs were ordered on all patients irrespective of the determination of the rule. The rules were interpreted by the primary investigator on the basis of the data sheet and the final orthopaedist radiograph reading. Outcome measures of this study were: sensitivity, specificity, positive predictive value and negative predictive value of the OKR.

Results A total of 283 patients were enrolled in the study. 22 fractures (7.77%) were detected. The decision rule had a sensitivity of 0.95 (95% CI 0.77 to 0.99), and a specificity of 0.44 (95% CI 0.37 to 0.50). The potential reduction in use of radiography was estimated to be 41%. The OKR missed only one fracture.

Conclusion Prospective validation has shown that the OKR is a highly sensitive tool for detecting knee fractures and has the potential to reduce the number of radiographs in patients with acute knee injuries.