How Does the Slump Sitting Radiograph Increase Proportion of Segmental Instability and Kyphotic Alignment of Lumbar Degenerative Spondylolisthesis?

Objective: Clinical and radiographic degenerative spondylolisthesis (CARDS) classification was proposed to differentiate homogenous lumbar degenerative spondylolisthesis (LDS) subgroups. The sitting radiograph exhibited lumbar malalignment with maximum lumbar kyphosis, intervertebral kyphosis, and spondylolisthesis.This study aimed to assess the sitting radiograph for distribution of clinical and radiographic degenerative spondylolisthesis classification, and to elucidate its significance for exhibiting kyphotic alignment (CARDS type D) and segmental instability.Methods: A cohort of 101 patients with symptomatic lumbar degenerative spondylolisthesis (LDS) between September 2018 and December 2020 were recruited. The distribution and relibility of CARDS classification with or without sitting radiograph was assessed. The translational and angular range of motion and segmental instability was also evaluated. Univariate analysis of variance was used for multiple groups, and the least significant difference for two groups. Kappa consistency test of intrarater and interrater was evaluated for CARDS classification with or without sitting radiograph. Chi-square test was used to compare paried categorical data.Results: Utility of sitting radiographs for CARDS classification revealed higher percentage of type D than that without the sitting radiograph (p < 0.001). The sitting radiograph revealed a larger slip distance than the flexion radiograph (p = 0.003), as well as a lower slip angle than flexion radiograph (p < 0.001). The sitting-supine modality demonstrated the largest translational range of motion compared to the sitting-extension (p < 0.001) and flexion-extension modalities (p < 0.001). The sitting-supine modality showed larger angular range of motion than the flexion-extension modality (p < 0.001). The percentage of flexion, extension, upright, supine, and sitting radiograph to identify translational instability was higher than that without sitting radiograph (p < 0.001), as well as taking angular motion >= 10 degrees as an additional criterion for segmental instability (p < 0.001).Conclusion: The CARDS classification was reliable for LDS. The sitting radiograph showed maximal slip distance and kyphotic slip angle. Application of the sitting radiograph was necessary for evaluating segmental instability and kyphotic alignment of LDS.