Introduction: Segmental instability, or mobile spondylolisthesis, and non-mobile spondylolisthesis require different treatments due a differing load response. The most common measure assessed is dynamic translation (mm) on upright imaging with the most common cutoff being 3 mm. Often patients present without translational change on upright dynamic imaging but reduce on supine studies. In this study, translational slippage was compared in patients without segmental instability on X-ray and MRI to identify a subset of patients traditionally classified as stable that have instability better visualized during supine studies.
Methods: Institutional (IRB) approval was obtained for this prospective experimental study. Retrospective analysis of our Institutional imaging database was performed. The database was queried for patient lumbar flexion and extension radiograph reports from December 2018 through July 2024. 483 studies were identified. Patients with prior surgery, scoliosis, DISH, ankylosing spondylitis, and spondylolysis were excluded. Translational slippage was measured on X-ray and MRI, patient demographics were recorded.
Results: 114 patients with a net total of 185 levels of spondylolisthesis were included. The mean difference (delta) between x-ray and MRI across all levels was 1.9 mm. There was a significant difference between measurement on x-ray and MRI across all levels (P < 0.001). Multivariable regression modeling demonstrated a significant positive correlation between measurement of spondylolisthesis on x-ray and the Delta value regardless of level. There was a significantly increased mean translational slippage on x-ray in the surgical group compared to the non-surgical group with mean values of 5.01 mm and 4.09 mm respectively with a cutpoint delta value of 2.6mm (P < 0.001).
Conclusion : There is a significant reduction in lumbar spondylolisthesis during supine imaging even in patients without translation on dynamic upright imaging. Patients with a higher degree (mm) of listhesis reduce more on supine imaging with a value 2.6mm reduction being significant for a higher likelihood for progression to surgery.
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