Abstract: BACKGROUND: Percutaneous lumbar endoscopy is in full swing in China and even in the world. Transforaminal lateral approach is one of the most commonly used approaches in percutaneous lumbar endoscopic surgery, but the biomechanical effects of the relevant segments are rarely reported.  
OBJECTIVE: To investigate the biomechanical effects of different sizes (7.5 mm, 10 mm, 15 mm) of facet arthroplasty on related segments of lumbar spine by three-dimensional finite element simulation.
METHODS:  A three-dimensional finite element model of L3-L5 was established to verify its effectiveness. The arthroplasty of L4/5 lumbar vertebrae in percutaneous endoscopic surgery was simulated. The angle between the needle and the horizontal plane and the coronal plane was taken as the puncture target, and the base of L5 superior articular process was taken as the puncture target. According to the puncture path, the circular saw with the diameter of 7.5 mm, 10 mm and 15 mm was made respectively, so as to obtain three-dimensional finite element model formed at different diameters of the base of L5 superior articular process. The normal model, 7.5 mm, 10 mm and 15 mm diameter forming finite element models were loaded in six directions to calculate the von Mises stress extremum and range of motion of the operating segments (L4/5) and adjacent segments (L3/4) of the three models under six states of flexion, extension, left flexion, right flexion, left rotation and right rotation. Relevant comparative studies were conducted to determine the effect of different sizes of facet arthroplasty on the biomechanical stability of lumbar spine.  
RESULTS AND CONCLUSION: (1) The effect on the operating segment (L4/5): The maximum stress of L4/5 disc with 15 mm diameter of L5 superior articular process was significantly increased under six working conditions of flexion, extension, left-right lateral bending and left-right rotation compared with that of 7.5 mm and 10 mm diameter of L4/5. The maximum stress of L4/5 disc with 15 mm diameter of L5 superior articular process was increased by 110%, 95% and 97% respectively. The range of motion of L4/5 segment of L5 with 15 mm diameter was greater than that of 7.5 mm and 10 mm diameter, which increased by 8.6%, 21.8%, 8.9%, 17.6%, 35.7% and 21.4% respectively. (2) Effect on adjacent segment (L3/4): The maximum stress of adjacent segment L3/4 disc with 15 mm diameter of L5 superior articular process increased compared with 7.5 mm and 10 mm diameter of L5 superior articular process in six working conditions, in which flexion was the most obvious, and the maximum stress of L3/4 disc increased by 29.3% compared with normal model. The range of motion of adjacent segment L3/4 of different sizes (7.5 mm, 10 mm, 15 mm) of zygapoplasty in flexion, extension, left-right lateral bending and left-right rotation was not significantly increased compared with normal model. (3) It is concluded that compared with 7.5 mm and 10 mm in diameter, 15 mm in diameter has a greater mechanical effect on the operating segment, and even has a corresponding effect on the stress of adjacent segments.

Key words:  , lumbar percutaneous endoscopy, foraminoplasty, three-dimensional finite element, biomechanics, stress