Evaluation of Indirect Decompression Effect After Extreme Lateral Lumbar Interbody Fusion Using Three‐Dimensional Volumetric Measurements—A Retrospective Study

ABSTRACT Background Two‐dimensional (2D) radiographic methods are suggested for evaluating radiographic outcomes following indirect decompression via extreme lateral interbody fusion (XLIF). Nonetheless, assessing neural decompression in a single imaging plane could potentially lead to an underestimation of the effects on central canal and foraminal volumes. Objective This study aims to evaluate the radiographic changes associated with XLIF procedures using three‐dimensional (3D) volumetric measurements and to investigate the effect of indirect decompression achieved through this procedure. Methods The retrospective clinical and radiological data of 44 patients between June 2019 and June 2022 who underwent single‐ or multilevel XLIF were analyzed. Preoperative and postoperative computed tomography (CT) scans facilitated 3D reconstructions. The effect of indirect decompression, manifesting as the elevation of the cranial vertebra, was quantified by measuring the volumetric change in the spinal canal, calculated through the subtraction of the spinal canal's geometry from a cylinder predefined both preoperatively and postoperatively. The relationship between these volumetric changes and clinical outcomes was then determined. Correlations between changes in volumetric measurements and clinical outcomes were assessed using Pearson's or Spearman's correlation coefficients, depending on the data distribution. Results Change in the spinal canal volume (Δ V ) due to the XLIF proved to be significant (mean Δ V  = 1629.28 ± 775.43 mm 3 , n  = 44, p  < 0.05). A significant, positive correlation was found between ΔV significant association between pain intensity (low back and leg pain) and the magnitude of the volumetric increase of the spinal canal was shown ( p  < 0.05 for LP and ODI, p  = 0.06 for LBP). Conclusion The developed method demonstrates accuracy, reproducibility, and applicability for analyzing XLIF, with significant potential for application in other spinal surgical methods. The volumetric changes exhibit predictive capability regarding the extent of indirect spinal canal decompression. A larger Δ V correlates with greater clinical benefits observed in XLIF surgery.