title: Derivation of a decision rule for the use of radiography in acute knee injuries.
abstract: OBJECTIVE
  To derive a highly sensitive decision rule for the selective use of radiography in acute knee injuries.
  
  
  METHODS
  Prospectively administered survey.
  
  
  METHODS
  Emergency departments of two university hospitals.
  
  
  METHODS
  Convenience sample of 1,047 adults with acute knee injuries.
  
  
  RESULTS
  Attending emergency physicians assessed each patient for 23 standardized clinical findings, which were recorded on data collection forms. A total of 127 patients was examined independently by two physicians to determine interobserver agreement. The outcome measure was fracture of the knee. Any patients who did not have ED 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 fracture (highest chi 2 values) were further analyzed by a recursive-partitioning 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) inability to flex to 90 degrees, and (5) inability to bear weight both immediately and in the ED (four steps). The presence of one or more of these findings would have identified the 68 fractures in the study population with a sensitivity of 1.0 (95% confidence interval [Cl], .95 to 1.0) and a specificity of .54 (95% Cl, .51 to .57). Application of the rule would have led to a 28.0% relative reduction in the use of radiography from 68.6% to 49.4% in the study population.
  
  
  CONCLUSIONS
  A practical, highly sensitive, and reliable decision rule for the use of radiography in acute knee injuries has been derived. Clinical application should await prospective validation of the rule.
authors.affiliation: Department of Medicine, University of Ottawa, Ontario, Canada.
authors.forename: I G
authors.initials: IG
authors.lastname: Stiell
authors.forename: G H
authors.initials: GH
authors.lastname: Greenberg
authors.forename: G A
authors.initials: GA
authors.lastname: Wells
authors.forename: R D
authors.initials: RD
authors.lastname: McKnight
authors.forename: A A
authors.initials: AA
authors.lastname: Cwinn
authors.forename: T
authors.initials: T
authors.lastname: Cacciotti
authors.forename: I
authors.initials: I
authors.lastname: McDowell
authors.forename: N A
authors.initials: NA
authors.lastname: Smith
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D003661:Decision Support Techniques; D004636:Emergency Service, Hospital; D005260:Female; D050723:Fractures, Bone / Q000000981:diagnostic imaging; D017408:Guidelines as Topic; D006801:Humans; D007718:Knee Injuries / Q000000981:diagnostic imaging*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011859:Radiography; D011795:Surveys and Questionnaires