Abstract: BACKGROUND: Endoscopic treatment of lumbar disc herniation has obvious advantages over traditional open surgery. Endoscopic surgery involves the implantation of a working cannula, which requires only partial bone removal, and there are no studies on the effects of two types of intraoperative foraminoplasty and laminoplasty on the mechanical properties of the local structure of the lumbar spine.  
OBJECTIVE: To compare the effect of foraminoplasty and laminoplasty on the biomechanical properties of disc and isthmus of the responsible segment.
METHODS: The lumbosacral CT images of a healthy male volunteer were taken, and a finite element model M0 of the L3 to sacral vertebrae was established, on which the primary and secondary foraminoplasty models M1 and M2 of the L5/S1 and the laminoplasty model M3 were built. The same load was applied to compare the intervertebral motion range, disc Von Mises stress and equivalent stress characteristics of L5 vertebral isthmus with each model.  
RESULTS AND CONCLUSION: (1) Compared with M0, M1 and M2 motion range in L5/S1 segment did not change significantly in all directions; M2 overall motion range increased by 8.60% in flexion; M3 increased by 8.23% and 8.26% in L5/S1 right bending and right torsion, and 5.39% and 5.67% in overall motion range in flexion and right bending, with no significant changes in motion range in the rest of working conditions. (2) Compared with M0, M1 showed no significant change in the extremes of Von Mises stress at L5/S1 disc; M2 increased 11.06%, 12.50%, 18.32%, and 15.48% in flexion, extension, left torsion, and right torsion; M3 increased 12.22%, 19.54%, 10.05%, and 9.97% in flexion, extension, left torsion, and right torsion, and the rest working conditions and L4/5 disc maximum Von Mises stress did not change significantly. (3) Compared to M0, the maximum Von Mises stress in the left isthmus of L5 of M1 increased by 12.43% in left bending, 18.38%, 13.29%, 13.62%, and 40.00% in the right isthmus in extension, right bending, left torsion, and right torsion. The maximum Von Mises stress in the left isthmus of L5 of M2 increased by 38.87%, 42.63%, 16.95%, and 19.35%, and that in the right isthmus increased by 12.58%, 33.70%, 12.92%, and 17.42% in flexion, extension, left bending, and left torsion. The maximum Von Mises stress in the left isthmus of L5 of M3 increased 67.07%, 78.14%, 32.33%, 62.94%, and 89.99% in flexion, extension, left and right bending, and right torsion. (4) The results suggest that foraminoplasty and laminoplasty have a small effect on spinal motion range; there is a mild increase in the extreme values of disc Von Mises stress in the segments operated by interbody laminoplasty and secondary foraminoplasty; there is no significant change in the extreme values of disc Von Mises stress in adjacent segments, and there is a significant increase in the Von Mises stress in the ipsilateral isthmus operated by the interbody laminoplasty model.

Key words: spinal endoscopy, lumbar disc herniation, foraminoplasty, laminoplasty, biomechanics, finite element analysis