Pan Cheng-Tang, Lin Che-Hsin, Huang Ya-Kang, Jang Jason S C, Lin Hsuan-Kai, Kuo Che-Nan, Lin De-Yao, Huang Jacob C
Department of Mechanical and Electro-Mechanical Engineering, National Sun Yat-Sen University, Kaohsiung City 80424, Taiwan.
Institute of Precision Medicine, National Sun Yat-Sen University, Kaohsiung City 80424, Taiwan.
Micromachines (Basel). 2021 Mar 15;12(3):307. doi: 10.3390/mi12030307.
Intervertebral fusion surgery for spinal trauma, degeneration, and deformity correction is a major vertebral reconstruction operation. For most cages, the stiffness of the cage is high enough to cause stress concentration, leading to a stress shielding effect between the vertebral bones and the cages. The stress shielding effect affects the outcome after the reconstruction surgery, easily causing damage and leading to a higher risk of reoperation. A porous structure for the spinal fusion cage can effectively reduce the stiffness to obtain more comparative strength for the surrounding tissue. In this study, an intervertebral cage with a porous gradation structure was designed for Ti64ELI alloy powders bonded by the selective laser melting (SLM) process. The medical imaging software InVesalius and 3D surface reconstruction software Geomagic Studio 12 (Raindrop Geomagic Inc., Morrisville, NC, USA) were utilized to establish the vertebra model, and ANSYS Workbench 16 (Ansys Inc., Canonsburg, PA, USA) simulation software was used to simulate the stress and strain of the motions including vertical body-weighted compression, flexion, extension, lateral bending, and rotation. The intervertebral cage with a hollow cylinder had porosity values of 80-70-60-70-80% (from center to both top side and bottom side) and had porosity values of 60-70-80 (from outside to inside). In addition, according to the contact areas between the vertebras and cages, the shape of the cages can be custom-designed. The cages underwent fatigue tests by following ASTM F2077-17. Then, mechanical property simulations of the cages were conducted for a comparison with the commercially available cages from three companies: Zimmer (Zimmer Biomet Holdings, Inc., Warsaw, IN, USA), Ulrich (Germany), and B. Braun (Germany). The results show that the stress and strain distribution of the cages are consistent with the ones of human bone, and show a uniform stress distribution, which can reduce stress concentration.
用于脊柱创伤、退变及畸形矫正的椎间融合手术是一项主要的椎体重建手术。对于大多数椎间融合器而言，其刚度足够高，会导致应力集中，进而在椎体骨与椎间融合器之间产生应力遮挡效应。应力遮挡效应会影响重建手术后的效果，容易造成损伤并导致再次手术的风险更高。具有多孔结构的脊柱融合器可以有效降低刚度，从而为周围组织获取更大的相对强度。在本研究中，针对通过选择性激光熔化（SLM）工艺粘结的Ti64ELI合金粉末设计了一种具有多孔渐变结构的椎间融合器。利用医学成像软件InVesalius和3D表面重建软件Geomagic Studio 12（美国北卡罗来纳州莫里斯维尔市Raindrop Geomagic公司）建立椎体模型，并使用ANSYS Workbench 16（美国宾夕法尼亚州卡农斯堡市Ansys公司）模拟软件来模拟包括垂直体重压缩、前屈、后伸、侧弯和旋转等运动的应力和应变。具有空心圆柱体结构的椎间融合器（从中心到顶部和底部两侧）的孔隙率值为80 - 70 - 60 - 70 - 80%，（从外部到内部）孔隙率值为60 - 70 - 80。此外，根据椎体与椎间融合器之间的接触面积，可以定制设计椎间融合器的形状。这些椎间融合器按照ASTM F2077 - 17标准进行疲劳测试。然后，对椎间融合器进行力学性能模拟，并与来自三家公司（美国印第安纳州华沙市的捷迈邦美公司、德国的乌尔里希公司和德国的贝朗公司）的市售椎间融合器进行比较。结果表明，椎间融合器的应力和应变分布与人体骨骼的应力和应变分布一致，且应力分布均匀，可降低应力集中。
