title: Reliability and development of a new classification of lumbosacral spondylolisthesis.
abstract: BACKGROUND
  A classification of lumbosacral spondylolisthesis has been proposed recently. This classification describes eight distinct types of spondylolisthesis based on the slip grade, the degree of dysplasia, and the sagittal sacro-pelvic balance. The objectives of this study are to assess the reliability of this classification and to propose a new and refined classification.
  
  
  METHODS
  Standing posteroanterior and lateral radiographs of the spine and pelvis of 40 subjects (22 low-grade, 18 high-grade) with lumbosacral spondylolisthesis were reviewed twice by six spine surgeons. Each radiograph was classified based on the slip grade, the degree of dysplasia, and the sagittal sacro-pelvic balance. No measurements from the radiographs were allowed. Intra- and inter-observer reliability was assessed using kappa coefficients. A refined classification is proposed based on the reliability study.
  
  
  RESULTS
  All eight types of spondylolisthesis described in the original classification were identified. Overall intra- and inter-observer agreement was respectively 76.7% (kappa: 0.72) and 57.0% (kappa: 0.49). The specific intra-observer agreement was 97.1% (kappa: 0.94), 85.0% (kappa: 0.69) and 88.8% (kappa: 0.85) with respect to the slip grade, the degree of dysplasia, and the sacro-pelvic balance, respectively. The specific inter-observer agreement was 95.2% (kappa: 0.90), 72.2% (kappa: 0.43) and 77.2% (kappa: 0.69) with respect to the slip grade, the degree of dysplasia, and the sacro-pelvic balance, respectively.
  
  
  CONCLUSIONS
  This study confirmed that surgeons can classify radiographic findings into all eight types of spondylolisthesis. The intra-observer reliability was substantial, while the inter-observer reliability was moderate mainly due to the difficulty in distinguishing between low- and high-dysplasia. A refined classification excluding the assessment of dysplasia, while incorporating the assessment of the slip grade, sacro-pelvic balance and global spino-pelvic balance is proposed, and now includes five types of lumbosacral spondylolisthesis.
authors.affiliation: Department of Surgery, University of Montreal, Montreal, Canada.|Division of Orthopedic Surgery, Hôpital du Sacré-Coeur, Montreal, Canada.|Division of Orthopedic Surgery, CHU Sainte-Justine, Montreal, Canada.
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Mac-Thiong
authors.affiliation: Department of Surgery, University of Montreal, Montreal, Canada.|Division of Orthopedic Surgery, CHU Sainte-Justine, Montreal, Canada.
authors.forename: Hubert
authors.initials: H
authors.lastname: Labelle
authors.affiliation: Department of Surgery, University of Montreal, Montreal, Canada.|Division of Orthopedic Surgery, Hôpital du Sacré-Coeur, Montreal, Canada.|Division of Orthopedic Surgery, CHU Sainte-Justine, Montreal, Canada.
authors.forename: Stefan
authors.initials: S
authors.lastname: Parent
authors.affiliation: Department of Orthopaedic Surgery, Boston Children Hospital, Harvard University, USA.
authors.forename: Michael Timothy
authors.initials: MT
authors.lastname: Hresko
authors.affiliation: Department of Orthopaedic Surgery, San Francisco General Hospital, UCSF, SF, USA.
authors.forename: Vedat
authors.initials: V
authors.lastname: Deviren
authors.affiliation: Department of Orthopaedic Surgery, Columbia University, New York Presbyterian Hospital, NY, USA.
authors.forename: Mark
authors.initials: M
authors.lastname: Weidenbaum