DERIVATION OF A DECISION RULE FOR THE USE OF RADIOGRAPHY IN ACUTE KNEE INJURIES

Study objective: To derive a highly sensitive decision rule for the se lective use of radiography in acute knee injuries. Design: Prospective ly administered survey. Setting: Emergency departments of two universi ty hospitals. Participants: Convenience sample of 1,047 adults with ac ute knee injuries. Results: Attending emergency physicians assessed ea ch patient for 23 standardized clinical findings, which were recorded on data collection forms. A total of 127 patients was examined indepen dently by two physicians to determine interobserver agreement. The out come measure was fracture of the knee. Any patients who did not have E D radiography underwent a structured telephone interview to determine the possibility of a missed fracture. Those variables found to be both reliable (highest kappa values) and strongly associated with a fractu re (highest chi(2) values) were further analyzed by a recursive-partit ioning multivariate technique. The derived decision rule included the following variables: (1) age 55 years or older, (2) tenderness at the head of the fibula, (3) isolated tenderness of the patella, (4) inabil ity to flex to 90 degrees, and (5) inability to bear weight both immed iately and in the ED (four steps). The presence of one or more of thes e findings would have identified the 68 fractures in the study populat ion with a sensitivity of 1.0 (95% confidence interval [CI], .95 to 1. 0) and a specificity of .54 (95% CI,.51 to .57). Application of the ru le would have led to a 28.0% relative reduction in the use of radiogra phy from 68.6% to 49.4% in the study population. Conclusion: A practic al, highly sensitive, and reliable decision rule for the use of radiog raphy in acute knee injuries has been derived. Clinical application sh ould await prospective validation of the rule.