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Reliability of the Spinal Deformity Study Group Classification of Lumbosacral Spondylolisthesis

Mac-Thiong, Jean-Marc, MD PhD*,†; Duong, Luc, PhD†,‡; Parent, Stefan, MD, PhD*,†; Hresko, Michael Timothy, MD§; Dimar, John R., MD; Weidenbaum, Mark, MD; Labelle, Hubert, MD*,†

doi: 10.1097/BRS.0b013e3182233969

Study Design. Reliability study of the computer-assisted SDSG (Spinal Deformity Study Group) classification of lumbosacral spondylolisthesis.

Objective. To assess the intra- and interobserver reliability of the computer-assisted SDSG classification of lumbosacral spondylolisthesis.

Summary of Background Data. The SDSG has proposed a new classification of lumbosacral spondylolisthesis based on slip grade, pelvic incidence (PI), and sacro-pelvic and spinal balance. Three types of low-grade spondylolisthesis are described: low PI (type 1), normal PI (type 2), and high PI (type 3). High-grade spondylolisthesis are defined as type 4 (balanced sacro-pelvis), type 5 (retroverted sacro-pelvis with balanced spine), and type 6 (retroverted sacro-pelvis with unbalanced spine).

Methods. Full-length standing lateral radiographs of the spine of 40 subjects with lumbosacral spondylolisthesis were reviewed twice by 7 observers. Custom software was used by the observers to identify 7 anatomical landmarks on each radiograph to determine the SDSG type for all subjects. Percentage of agreement and κ coefficients were used to determine the intra- and interobserver reliability.

Results. All 6 types of spondylolisthesis described in the computer-assisted SDSG classification were identified. Overall intra- and interobserver agreements were 80% (κ: 0.74) and 71% (κ: 0.65), respectively. The intra- and interobserver agreements associated with computerized determination of slip grade were 92% (κ: 0.83) and 88% (κ: 0.78), respectively. As for computerized determination of sacro-pelvic and spinal balance, intra- and interobserver agreements were 86% (κ: 0.76) and 75% (κ: 0.63) for low-grade slips, whereas they were 88% (κ: 0.80) and 83% (κ: 0.75) for high-grade slips.

Conclusion. Substantial intra- and interobserver reliability was found for the computer-assisted SDSG classification, and all 6 types of lumbosacral spondylolisthesis were identified. Refinement of the computer-assisted classification technique is, however, needed to further increase the reliability of the SDSG classification and facilitate its clinical use.

This study evaluates the reliability of the computer-assisted Spinal Deformity Study Group (SDSG) classification of lumbosacral spondylolisthesis on the basis of slip grade, pelvic incidence (PI), and sacropelvic and spinal balance. Substantial intra- and interobserver reliability was found, and all 6 types of spondylolisthesis described in the classification were observed.

*Department of Surgery, University of Montreal, Montreal, Canada

Research Center, CHU Sainte-Justine, Montreal, Canada

Département de genie logiciel et des technologies de l'information, École de Technologie Supérieure, Montreal, Canada

§Department of Orthopaedic Surgery, Children's Hospital Boston, Harvard University, MA

Leatherman Spine Center, KY

Department of Orthopaedic Surgery, Columbia University, New York Presbyterian Hospital, New York, NY.

Address correspondence and reprint requests to Jean-Marc Mac-Thiong, MD, PhD, Division of Orthopaedics, CHU Sainte-Justine, 3175 Côte-Sainte-Catherine, Montréal, Québec, Canada H3T 1C5; E-mail:

Acknowledgment date: March 22, 2010. First revision date: February 27, 2010; Second revision date: March 10, 2011; Third revision date: April 16, 2011. Acceptance date: April 25, 2011.

The manuscript submitted does not contain information about medical device(s)/drug(s).

Corporate/Industry funds were received in support of this work.

One or more of the author(s) has/have received or will receive benefits for personal or professional use from a commercial party related directly or indirectly to the subject of this manuscript: e.g., honoraria, gifts, consultancies, royalties, stocks, stock options, decision-making position.

Supported by the Spinal Deformity Study Group.

Funded by an educational/research grant from Medtronic Sofamor Danek.

© 2012 Lippincott Williams & Wilkins, Inc.