Validation and Reliability Analysis of the New SRS-Schwab Classification for Adult Spinal Deformity

STUDY DESIGN: An inter- and intra-observer reliability study. OBJECTIVE: To determine the inter- and intra-observer reliabilities of the new SRS-Schwab system for classifying adult spinal deformity (ASD) using nonpremarked cases. SUMMARY OF BACKGROUND DATA: Schwab et al reported excellent inter- and intra-observer reliability and interobserver agreement for classification based on curve type and 3 modifiers. METHODS: A total of 102 patients with ASD were included in this study, which was conducted from February 2009 to January 2012. Long-cassette standing posterior-anterior and lateral radiographs of the spine and the pelvis were obtained from patients with ASD in the fist-on-clavicle position. All 102 cases were classified according to the new SRS-Schwab classification by 4 observers. After a 2-week interval, the same classification was independently repeated by each observer with the cases in a different randomly assigned order. The Fless κ coefficient was calculated to test the inter- and intra-observer reliabilities of the new SRS-Schwab classification. RESULTS: With the new SRS-Schwab classification system, 12 patients were classified as having a type T curve, 30 cases as having a type L, 45 cases as having a type D, and 15 cases as having a type S. For overall classification, the mean κ value was 0.73 for interobserver reliability and 0.83 for intraobserver reliability. Disagreements occurred most often when differentiating type T curves from type L curves and when determining the pelvic incidence minus lumbar lordosis modifier. CONCLUSION: With the nonpremarked cases, this new SRS-Schwab system for patients with ASD could achieve good to excellent intra- and inter-observer reliability, but the definition of thoracic or lumbar curves was still predisposed to confusion. Overall, the SRS-Schwab system is a simple and clear classification system with incorporated spinopelvic parameters, which significantly increase its value for practical usage.