Differential Fusion Techniques in Uninstrumented Posterolateral Lumbar Fusion: A Retrospective Self-Control Study, Technical Notes and Radiological Outcomes

Objective: To compare two surgical techniques, the “bread and jam” and “reverse sandwich,” for uninstrumented posterolateral lumbar fusion in treating degenerative lumbar spine disease, focusing on their impact on fusion outcomes. Materials and Methods: This retrospective study at Siriraj Hospital analyzed data from patients undergoing uninstrumented posterolateral lumbar fusion between January 2002 and December 2016. Procedures were performed by a senior spine surgeon using posterior midline approaches with iliac bone grafting customized to each patient. Radiographic assessments at 3, 6, 9, 12, and 24 months postoperatively evaluated fusion mass sizes, assessed independently for reliability. Results: Sixty patients (50 women, mean age 63.17 years) were included, predominantly diagnosed with spinal stenosis with spondylolisthesis (79.66%). The main symptoms were radiculopathy (47.46%) and neurogenic claudication (40.68%). Most surgeries targeted one spinal level (71.19%). Fusion mass size differed significantly between the right and left sides at 3, 9, and 24 months, with the right side consistently larger. However, no significant differences were noted at 6 and 12 months. Conclusion: The “reverse sandwich” technique, incorporating cancellous bone on both sides of the graft, potentially enhances fusion outcomes compared to the “bread and jam” technique, which uses cancellous bone on one side. This dual-sided approach in the “reverse sandwich” technique, may improve vascularization and foster a more favorable biological environment for fusion without apparent biomechanical differences observed in this study. Further research is needed to corroborate these findings and elucidate their biological mechanisms.