Fate of the L5-S1 Disc After Thoracolumbar Fusion Ending at L5: A >5-Year Magnetic Resonance Imaging (MRI) Follow-Up Study

Purpose: This retrospective cohort study aimed to evaluate the outcomes of long thoracolumbar fusions ending at L5, focusing on revision rates and the long-term evolution of the L5-S1 disc on magnetic resonance imaging (MRI) at a minimum five-year follow-up.Overview of literature: The decision of whether to stop a long thoracolumbar fusion at L5 or extend it to the sacrum remains highly debated due to concerns regarding adjacent segment degeneration and the subsequent need for revision surgery.Methods: A retrospective review included 12 patients who underwent thoracolumbar fusion ending at L5 between 2007 and 2018.L5-S1 MRI Pfirrmann grades were assessed preoperatively and at the final followup.Oswestry Disability Index (ODI) scores, as well as pre-and postoperative radiographic spinopelvic parameters, were also recorded.Results: Revision surgery with extension of the fusion to the sacrum was required in 41.6% of patients.Among the non-reoperated patients, 57% demonstrated progression of L5-S1 disc degeneration.The need for revision surgery was most frequently associated with preoperative sagittal imbalance.Conclusions: Stopping a long thoracolumbar fusion at L5 may not be appropriate for patients requiring significant sagittal correction, particularly in older individuals.