Iliocava junction to L4-L5 disc anatomical relationship in L5-S1 isthmic spondylolisthesis

Background: Anterior lumbar interbody fusion finds a place in L5-S1 isthmic spondylolisthesis (ISPL) treatment. Extension of this arthrodesis at L4-L5 level is sometimes required. Anterior approach of the L4L5 disc is considered difficult due to the anatomical relationship between the iliocava junction (ICJ) and the spine. Hypothesis: Does the lumbosacral deformation induced by ISPL allows anterior approach of L4-L5 disc between the iliac? Study design: Retrospective radiographic analysis of consecutive patients. Methods: This retrospective imaging study of a continuous series of 97 patients treated for an L5-S1 ISPL involved radiological parameters specific to ISPL and pelvic-sagittal balance. The distance between the ICJ and the L4 lower endplate was measured in millimeters. The factors influencing this distance were sought in order to identify a predictive model of high ICJ. Results: The ICJ took a cranial position with respect to the L4-L5 disc with an average distance of 1.8 mm +/- 16.4. This distance was statistically higher in the case of high-grade ISPL (p < 0.01). The high ICJ position was correlated with a high Taillard index (r=0.39; CI95% [0.13; 0.61]; p < .001) and a low lumbar-sacral angle (LSA) (r = -0.33; CI95% [ -0.56; -0.06]; p < 0.01). Among the parameters specific to spino-pelvic statics, pelvic incidence, pelvic tilt and lumbar lordosis had similar correlations (r> 0.30). Conclusion: ISPL induces a geometric deformation of the lumbosacral hinge which modifies its anatomical relations with the ICJ. The anterior approach technique of L4-L5 disc in the presence of an L5-S1 ISPL is possible between the iliac veins for the large displacement and low LSA forms. (C) 2020 Elsevier Masson SAS. All rights reserved.