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Scoliosis Research Society—Schwab Adult Spinal Deformity Classification: A Validation Study

Schwab, Frank, MD*; Ungar, Benjamin, BA*; Blondel, Benjamin, MD*; Buchowski, Jacob, MD; Coe, Jeffrey, MD; Deinlein, Donald, MD§; DeWald, Christopher, MD; Mehdian, Hossein, MD; Shaffrey, Christopher, MD; Tribus, Clifford, MD**; Lafage, Virginie, PhD*

doi: 10.1097/BRS.0b013e31823e15e2
Health Services Research

Study Design. Inter- and intra-rater variability study.

Objective. On the basis of a Scoliosis Research Society effort, this study seeks to determine whether the new adult spinal deformity (ASD) classification system is clear and reliable.

Summary of Background Data. A classification of adult ASD can serve several purposes, including consistent characterization of a clinical entity, a basis for comparing different treatments, and recommended treatments. Although pediatric scoliosis classifications are well established, an ASD classification is still being developed. A previous classification developed by Schwab et al has met with clinical relevance but did not include pelvic parameters, which have shown substantial correlation with health-related quality of life measures in recent studies.

Methods. Initiated by the Scoliosis Research Society Adult Deformity Committee, this study revised a previously published classification to include pelvic parameters. Modifier cutoffs were determined using health-related quality of life analysis from a multicenter database of adult deformity patients. Nine readers graded 21 premarked cases twice each, approximately 1 week apart. Inter- and intra-rater variability and agreement were determined for curve type and each modifier separately. Fleiss' kappa was used for reliability measures, with values of 0.00 to 0.20 considered slight, 0.21 to 0.40 fair, 0.41 to 0.60 moderate, 0.61 to 0.80 substantial, and 0.81 to 1.00 almost perfect agreement.

Results. Inter-rater kappa for curve type was 0.80 and 0.87 for the 2 readings, respectively, with modifier kappas of 0.75 and 0.86, 0.97 and 0.98, and 0.96 and 0.96 for pelvic incidence minus lumbar lordosis (PI-LL), pelvic tilt (PT), and sagittal vertical axis (SVA), respectively. By the second reading, curve type was identified by all readers consistently in 66.7%, PI-LL in 71.4%, PT in 95.2%, and SVA in 90.5% of cases. Intra-rater kappa averaged 0.94 for curve type, 0.88 for PI-LL, 0.97 for PT, and 0.97 for SVA across all readers.

Conclusion. Data from this study show that there is excellent inter- and intra-rater reliability and inter-rater agreement for curve type and each modifier. The high degree of reliability demonstrates that applying the classification system is easy and consistent.

There is a need for a comprehensive, clinically relevant adult spinal deformity classification. A previous classification has been revised to include pelvic parameters, which have shown marked correlation with health-related quality of life measures in recent studies. This study demonstrates that the proposed Scoliosis Research Society–Schwab classification is clear, with excellent intra- and inter-rater reliability.

*NYU Hospital for Joint Diseases, New York, NY;

Washington University in St. Louis, St. Louis, MO;

Silicon Valley Spine Institute, Campbell, CA;

§The University of Alabama at Birmingham, Birmingham, AL;

Rush University Medical Center, Chicago, IL;

Queens Medical Centre, Nottingham, United Kingdom;

University of Virginia, Charlottesville, VA; and

**University of Wisconsin-Madison, Madison, WI.

Address correspondence and reprint requests to Virginie Lafage, PhD, NYU Hospital for Joint Diseases, 306 E. 15th St., Ste. 1F, New York, NY 10003; E-mail:

Acknowledgment date: July 15, 2011. First revision date: September 21, 2011. Acceptance date: October 12, 2011.

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

No funds were received in support of this work.

No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript.

© 2012 Lippincott Williams & Wilkins, Inc.