title: The Subaxial Cervical Spine Injury Classification System: an external agreement validation study.
abstract: BACKGROUND
  In 2007, the Subaxial Cervical Spine Injury Classification (SLIC) system was introduced demonstrating moderate reliability in an internal validation study.
  
  
  OBJECTIVE
  To assess the agreement on the SLIC system using clinical data from a spinal trauma population and whether the SLIC treatment algorithm outcome improved agreement on treatment decisions among surgeons.
  
  
  METHODS
  An external classification validation study.
  
  
  METHODS
  Twelve spinal surgeons (five consultants and seven fellows) assessed 51 randomly selected cases.
  
  
  METHODS
  Raw agreement, Fleiss kappa, and intraclass correlation coefficient statistics were used for reliability analysis. Majority rules and latent class modeling were used for accuracy analysis.
  
  
  METHODS
  Fifty-one randomly selected cases with significant injuries of the cervical spine from a prospective consecutive series of trauma patients were assessed using the SLIC system. Neurologic details, plain radiographs, and computed tomography scans were available for all cases as well as magnetic resonance imaging in 21 cases (41%). No funds were received in support of this study. The authors have no conflict of interest in the subject of this article.
  
  
  RESULTS
  The inter-rater agreement on the most severely affected level of injury was strong (κ=0.76). The agreement on the morphologic injury characteristics was poor (κ=0.29) and agreement on the integrity of the discoligamentous complex was average (κ=0.46). The inter-rater agreement on the treatment verdict after the total SLIC injury severity score was slightly lower than the surgeons' agreement on personal treatment preference (κ=0.55 vs. κ=0.63). Latent class analysis was not converging and did not present accurate estimations of the true classification categories. Based on these findings, no second survey for testing intrarater agreement was performed.
  
  
  CONCLUSIONS
  We found poor agreement on the morphologic injury characteristics of the SLIC system, and its treatment algorithm showed no improved agreement on treatment decisions among surgeons. The authors discuss that the reproducibility of the SLIC system is likely to improve when unambiguous true morphologic injury characteristics are being implemented.
authors.affiliation: Stoke Mandeville Spinal Foundation, National Spinal Injuries Centre, Stoke Mandeville Hospital, Aylesbury, UK; Harris Manchester College, University of Oxford, Oxford, UK; Spine Unit, Department of Orthopaedics, Radboud University Nijmegen Medical Center, Nijmegen, The Netherlands. Electronic address: jvanmiddendorp@gmail.com.
authors.forename: Joost J
authors.initials: JJ
authors.lastname: van Middendorp
authors.forename: Laurent
authors.initials: L
authors.lastname: Audigé
authors.forename: Ronald H
authors.initials: RH
authors.lastname: Bartels
authors.forename: Ciaran
authors.initials: C
authors.lastname: Bolger
authors.forename: Hamish
authors.initials: H
authors.lastname: Deverall
authors.forename: Priyesh
authors.initials: P
authors.lastname: Dhoke
authors.forename: Carel H
authors.initials: CH
authors.lastname: Diekerhof
authors.forename: Geertje A M
authors.initials: GA
authors.lastname: Govaert
authors.forename: Vicente
authors.initials: V
authors.lastname: Guimerá
authors.forename: Heiko
authors.initials: H
authors.lastname: Koller
authors.forename: Stephen A C
authors.initials: SA
authors.lastname: Morris
authors.forename: Tony
authors.initials: T
authors.lastname: Setiobudi
authors.forename: Allard J F
authors.initials: AJ
authors.lastname: Hosman
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D002574:Cervical Vertebrae / Q000293:injuries*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013119:Spinal Cord Injuries / Q000209:etiology; D013124:Spinal Injuries / Q000145:classification* / Q000150:complications; D055815:Young Adult
keywords: Classification system; SLIC system; Spinal trauma; Subaxial cervical spine; Validation study