title: A CT-based classification of prior ACL femoral tunnel location for planning revision ACL surgery.
abstract: OBJECTIVE
  The purposes of this study are to describe an ACL femoral tunnel classification system for use in planning revision ACL reconstruction based on 3-D computed tomography (CT) reconstructions and to evaluate its inter- and intra-rater reliability.
  
  
  METHODS
  A femoral tunnel classification system was developed based on the location of the femoral tunnel relative to the lateral intercondylar ridge. The femoral tunnel was classified as Type I if it was located entirely below and posterior to the ridge as viewed from distally, Type II if it was slightly malpositioned (either vertically, anteriorly, or both), and Type III if it was significantly malpositioned. To evaluate the reproducibility of the classification system, CT scans of 27 knees were obtained from patients scheduled for revision ACL reconstruction, and 3-D reconstructions were created. Four views of the 3-D reconstruction of each femur were then obtained, and inter- and intra-observer reliability was determined following classification of the tunnels by eight observers.
  
  
  RESULTS
  Twenty-five tunnels were classified as Type I (5 tunnels), Type II (9 tunnels), or type III (11 tunnels) by at least 5 of 8 observers, while insufficient agreement was noted to classify two tunnels. The interobserver reliability of tunnel classification as type I, II, or III yielded a κ coefficient of 0.57, while intra-observer reliability yielded a κ coefficient of 0.67. Subclassification of type II femoral tunnels into the subgroups anterior, vertical, and both was possible in four of the nine type II patients. The interobserver reliability of the complete classification system yielded a κ coefficient of 0.50, while the intra-observer reliability yielded a κ coefficient of 0.54.
  
  
  CONCLUSIONS
  Classification of the location of ACL femoral tunnels utilizing 3-D reconstructions of CT data yields moderate to substantial inter- and intra-observer reliability.
  
  
  METHODS
  Diagnostic Level III.
authors.affiliation: Department of Orthopaedic Surgery, The Ohio State University School of Medicine, 2050 Kenny Road, Columbus, OH 45631, USA. robert.magnussen@gmail.com
authors.forename: Robert A
authors.initials: RA
authors.lastname: Magnussen
authors.forename: Pedro
authors.initials: P
authors.lastname: Debieux
authors.forename: Biju
authors.initials: B
authors.lastname: Benjamin
authors.forename: Sébastien
authors.initials: S
authors.lastname: Lustig
authors.forename: Guillaume
authors.initials: G
authors.lastname: Demey
authors.forename: Elvire
authors.initials: E
authors.lastname: Servien
authors.forename: Philippe
authors.initials: P
authors.lastname: Neyret
mesh_terms: D016118:Anterior Cruciate Ligament / Q000000981:diagnostic imaging* / Q000601:surgery*; D059549:Anterior Cruciate Ligament Reconstruction / Q000379:methods*; D005269:Femur / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional; D007719:Knee Joint / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D012086:Reoperation; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed