Summary: This study evaluates the reliability of the Spinal Deformity Study Group (SDSG) classification of lumbosacral spondylolisthesis based on slip grade, pelvic incidence, sacro‐pelvic and spinal balance. Substantial intra‐ and inter‐observer reliability was found, and all six types of spondylolisthesis described in the classification were observed. The reliability of the SDSG classification compares favorably with the reliability of other spinal classification systems.
Introduction: The SDSG has proposed a new classification of lumbosacral spondylolisthesis based on slip grade, pelvic incidence (PI), sacropelvic and spinal balance (Figure).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). This study evaluates the reliability of the SDSG classification of lumbosacral spondylolisthesis.
Methods: Full length standing lateral radiographs of the spine of 40 subjects with lumbosacral spondylolisthesis were reviewed twice by seven observers. Custom software was used by the observers to identify 7 anatomical landmarks on each radiograph, in order to determine the SDSG type for all subjects. Percentage of agreement and kappa coefficients were used to determine the intra‐ and inter‐observer reliability.
Results: All six types of spondylolisthesis described in the classification were identified. Overall intra‐ and inter‐observer agreements were 80% (kappa: 0.74) and 71% (kappa: 0.65), respectively. Intra‐ and inter‐observer agreements associated with determination of slip grade were 92% (kappa: 0.83) and 88% (kappa: 0.78), respectively. As for sacro‐pelvic and spinal balance, intra‐ and inter‐observer agreements were 86% (kappa: 0.76) and 75% (kappa: 0.63) for low‐grade slips, while they were 88% (kappa: 0.80) and 83% (kappa: 0.75) for high‐grade slips.
Conclusion: Substantial intra‐ and inter‐observer reliability was found for the SDSG classification, and all six types of spondylolisthesis were identified. Refinement of the computer‐assisted technique is expected to further increase the reliability of the classification and facilitate its clinical use.
Significance: There is a need for a reliable classification of spondylolisthesis since past classifications are inadequate for guiding treatment, resulting in significant variations in treatment plans. The SDSG classification is reliable and is designed to facilitate clinical evaluation of spondylolisthesis and therefore hopefully allow more comprehensive investigation of future progression and treatment of this pathology.