Abstract: BACKGROUND: Upper lumbar spinal stenosis is a multifactorial degenerative disorder of the spine. For narrowing of the spinal canal in the upper lumbar region (L1-L4), surgical decision-making is particularly complex. Existing minimally invasive surgeries each have their own advantages and limitations. Currently, there are few reports on biomechanical comparison and finite element analysis of different surgical methods for the treatment of high lumbar spinal stenosis. 
OBJECTIVE: To analyze the biomechanical impact of endoscopic unilateral laminotomy for bilateral decompression, transforaminal endoscopic lumbar decompression, and cross-overtop decompression in the treatment of upper lumbar spinal stenosis using endoscopy, and to verify the reliability and effectiveness of these three surgical techniques in treating upper lumbar spinal stenosis, providing a biomechanical basis for clinical decision-making.
METHODS: The CT images of the lumbar spine of a healthy volunteer were selected, and the finite element model M0 of the normal lumbar L1-L5 segments was established using Mimics, Geomagic, Solid works, and Ansys software. The L2-L3 segment, representing upper lumbar characteristics, was chosen. Based on this model, the surgical models for endoscopic unilateral laminotomy for bilateral decompression (M1), transforaminal endoscopic lumbar decompression (M2), and cross-overtop decompression (M3) were established. Using software, the changes in the range of motion of the entire lumbar segment and the maximum Von Mises stress of the intervertebral discs were simulated and evaluated for each group of models under six loading conditions: flexion, extension, left lateral bending, right lateral bending, left rotation, and right rotation.
RESULTS AND CONCLUSION: (1) Compared with model M0, the range of motion in M1, M2, and M3 increased under all six conditions, with M1 showing a greater increase. (2) M1 and M2 demonstrated significant increases in range of motion under forward bending, extension, and right rotation, while the increase under other conditions remained below 7%. (3) Compared with model M3, model M1 exhibited slightly increased overall joint range of motion during extension and left bending, while no significant changes were observed in other aspects, and the L1-L5 lumbar segments did not reach an unstable state. (4) In model M1, the maximum Von Mises stress of the intervertebral discs increased most significantly under flexion and extension loading conditions. However, under left lateral bending, right lateral bending, left rotation, and right rotation loading conditions, the increase did not exceed 5%. (5) These findings suggest that due to the sagittal anatomical characteristics of the facet joints, the unilateral laminotomy for bilateral decompression technique, while decompressing, involves resection of more facet joints, which impacts overall segmental stability. The transforaminal endoscopic lumbar decompression technique is suitable for patients with foraminal stenosis but cannot achieve complete decompression for those with severe ventral central stenosis. The Cross-Overtop technique effectively enlarges the volume of the central canal and lateral recess, optimizing decompression, and shows unique advantages in treating upper lumbar spinal stenosis.

Key words: upper lumbar spinal stenosis, spinal endoscopy, decompression surgery, biomechanics, finite element analysis