Diagnostic efficacy of nerve root sedimentation sign in post-lumbar interbody fusion patients: an imaging evaluation and modification.

Background: The sedimentation sign offers an efficient method for evaluating lumbar spinal stenosis. However, limited research exists regarding its applicability to post-operative MRI scans. This study aims to assess the viability of utilizing the nerve root sedimentation sign (NRSS) and Schizas classification (SC) in the evaluation of post-operative lumbar stenosis.

Methods: Patients were classified into seven groups using SC: A1, A2, A3, A4, B, C and D. The dural sac cross-sectional area (DSCA), anterior-posterior dural sac diameter (AP), and the Oswestry disability index (ODI) of each group were compared. The difference in DSCA between direct and indirect decompression surgery was also compared to confirm whether the deformation of the spinal canal will affect the results.

Results: 232 postoperative patients were evaluated. The variance of analysis showed that DCSA, AP and ODI had significant differences among the SC groups and NRSS groups postoperatively (P < 0.01). Comparison of DSCA results between direct and indirect decompression postoperative patients showed significant differences between groups A1 and A2, A2 and A3. AP comparison results showed significant differences between groups A1 and A2. ODI comparison results showed significant differences between groups A2 and A3. Among OLIF patients, groups A1 and A2 had mean DSCA values greater than 100mm, while in the T/PLIF group, groups A1-4 had mean DSCA values greater than 100mm.

Conclusion: Both sedimentation signs are applicable for the evaluation of postoperative lumbar spinal stenosis. We recommend updating the definition of negative nerve root sedimentation sign to nerve root sedimentation on the dorsal side of the dural sac, with an occupying area less than half, and greater than half considered positive sign. Sedimentation sign is mainly formed by the interaction of gravity, extradural pressure, and nerve root tension.