Three-dimensional finite element analysis of the influence of three subtypes of bone cement distribution on the postoperative stress of thoracolumbar vertebral body

English Keywords:Bone Cement  Diffusion Type  Vertebroplasty  Finite Element

English Abstract:

  【Abstract】 Objectives: Using finite element method to analyze the distribution changes of stress under different loads in three subtypes of diffuse-type bone cements after thoracolumbar vertebroplasty. Methods: To establish the finite element models of T11-L2-vertebral-function-unit compression fracture and three subtypes of diffuse-type bone cement based on the CT source data of bone cement of 1 patient with L1 spinal compression fracture and 3 patients undergone L1 vertebroplasty, presenting diffuse subtype, bulk subtype and mixed subtype respectively, and computed by Mimics 19.0, Geomagic Studio 2013, and Solid Works 2017 software. Using the method of finite element analysis, to simulate the weight of the upper half of a normal person after limited every activity of all the nodes under the L2 vertebral surface, and applied evenly 400N surface load on the T11 vertebra, with vertically downward pressure. At the same time, 10N·m torque was applied on the surface of the T11 vertebra with different directions, to simulate 6 movement conditions, namely anterior flexion, posterior extension, right-side bending, left-side bending, left lateral rotation and right lateral rotation. Also, pressure of 0.3MPa(lying flat), 1MPa(standing), and 4MPa(loading) were applied respectively on the T11 surface to simulate daily-life activities. The stress distribution of the 4 models under different load conditions was observed. Results: After the injection of bone cement, under different levels of pressures, the distribution, regarding the operated vertebra, of the bulk subtype bone cement was significantly higher than that of the diffuse subtype and mixed subtype. The stress of the operated vertebra showed a positive correlation to the increase of the pressure in 4 types of models. For 6 movement conditions, the distribution, regarding the operated vertebra, of the bulk subtype bone cement was significantly higher than that of the diffuse subtype and mixed subtype, and the stress of the operated vertebra of the mixed subtype was relatively lower. After applications of 0.3, 1, and 4MPa pressure, the operated vertebra with anterior flexion encountered the maximum stress, and the stress of the bulk subtype was the highest, which were 63.295MPa, 84.419MPa and 174.96MPa respectively, while that of the diffuse subtype were 62.348MPa, 80.974MPa and 160.95MPa, and that of the mixed subtype was 47.667MPa, 62.171MPa and 124.35MPa. Conclusions: The stress of the post-vertebroplasty vertebra is correlated to the pressure and the load directions. Bulk subtype bone cement is an important factor leading to the increase in stress of the operated vertebra. Bone cement with mixed subtype distribution is possibly a more ideal diffuse type.