低弹性模量骨水泥对骨质疏松压缩性骨折椎体及邻近椎体应力的影响:三维有限元分析

Effect of bone cement with a low elastic modulus on the fractured and adjacent vertebrae in patients with osteoporotic vertebral compression fractures: a three-dimensional finite analysis

背景:椎体成形及椎体后凸成形可有效修复骨质疏松性椎体压缩性骨折,但注入骨水泥强化后可使骨折椎体及邻近椎体应力改变易导致新发骨折。目的:应用三维有限元法分析不同弹性模量骨水泥注射椎体成形后骨折椎体及邻近椎体的应力变化。方法:选取1个有代表性的健康成年男性志愿者行腰椎CT扫描,将图像处理后导出应用Mimics进行三维重建,应用Geomagic对三维模型进行光滑、打磨、去噪,Ansys Workbench下装配实体模型,赋值后建立L_2-L_4段骨质疏松椎体压缩性骨折模型。设定在L_3椎体注入4 mL弹性模量分别为8 000,4 000,2 000及1 000 MPa的骨水泥,骨水泥在椎体中央呈球形分布。在L_2上表面施加500 N预载荷,附加弯矩为50 N?m,约束L_4下表面自由度。模拟L_2-L_4前屈、后伸、右屈及右侧轴向旋转4种运动状态,比较不同弹性模量骨水泥注射前后骨折椎体及上下邻近椎体的应力变化。结果与结论:骨水泥注射后骨折椎体及邻近椎体应力均较治疗前明显增加,随骨水泥弹性模量的增加骨折椎体应力也随之增大,而邻近椎体应力无明显变化。提示降低骨水泥弹性模量可能是减少椎体成形后因骨折椎体及邻近椎体应力变化而发生骨折的一种方法。

BACKGROUND： Vertebroplasty and kyphoplasty can effectively repair osteoporotic vertebral compression fractures, but bone cement injection can cause the change of stress in the fractured vertebrae and adjacent vertebrae after surgery, leading to new fractures. OBJECTIVE： To analyze the stress changes of the fractured vertebrae and adjacent vertebrae after vertebroplasty with different elastic modulus bone cement by a three-dimensional finite element method. METHODS： One healthy adult male volunteer was selected for lumbar spine CT scan. The acquired images were imported for three-dimensional reconstruction using Mimics. The three-dimensional model was smoothed, polished and denoised by Geomagic software, and then the solid mode was built under Workbench Ansys. An osteoporotic vertebral compression fracture model in L_（2-4） segments was established after assignment. Bone cement（4 m L） with different elastic moduli（8 000, 4 000, 2 000 and 1 000 MPa） injected into the L_3 segment distributed in the middle of the vertebrae as spherical shape. 500 N pre-load was applied on the L_2 surface with an additional bending moment of 50 N·m. The lower surface free degree of L_4 was restrained. The L_2-_4 forward flexion, posterior extension, right flexion and axial rotation on the right side were stimulated. The stress changes of the fractured vertebrae and the upper and lower adjacent vertebrae before and after bone cement injection with different elastic moduli were compared. RESULTS AND CONCLUSION： The stress of the fractured vertebrae and adjacent vertebrae were significantly increased compared with that before operation. With the increase of elastic modulus, the stress of the fractured vertebrae increased, but there were no changes in the stress of adjacent vertebrae. These findings indicate that the elastic modulus of bone cement may be a method to reduce new fractures of the fractured and adjacent vertebrae after bone cement injection.