[Biomechanical effects of different bone cement diffusion patterns after vertebroplasty:finite element analysis].

Objective: To investigate the biomechanical effects of different bone cement diffusion patterns in the treatment of osteoporotic vertebral compression fractures.

Methods: One volunteer with L1 osteoporotic vertebral compression fracture was selected, male, aged 68 years old, heighed 172 cm, weighted 60 kg, and healthy before. CT scans were used from T-L, CT data was extracted with Mimics software, and Geomagic wrap and Solidworks were used to model, and the three-dimensional finite element model (T-L) of preoperative osteoporotic vertebral compression fractures in the thoracolumbar segment was established. Similarly, the situations of bone cement dispersion in vertebroplasty were simulated (the situations of bone cement dispersion had the three kinds, including the bone cement not contacts with upper and lower endplates, the bone cement only contacts with upper endplates, and the bone cement contacts with upper and lower endplates). According to different diffusion situations, five types of loads were applied to the model:upright, upright plus forward flexion, upright plus backward extension, upright plus left bending, upright plus right rotation. Meanwhile, the model was compared with the cementless lumbar spine model, and the deformation and stress distribution of each model under load were recorded and compared.

Results: After the establishing the finite element model of osteoporotic vertebral compression fracture in the thoracolumbar segment, it was found that the deformation of three different bone cement distribution models above was not significantly different. In L cancellous bone, the Von Mises stress of the cementless lumbar spine group was significantly higher than that of the cemented group. Among the three groups of different bone cement injection situations, the Von Mises stress in the group of bone cement contacts with upper and lower endplates was the lowest, followed by the group of bone cement only contacts with upper endplates, and the highest Von Mises stress was the group that bone cement contacts neither the upper or lower endplates. In the comparison of bone cement stress, the Von Mises stress in the group of bone cement contacts with upper and lower endplates was significantly higher than the other two groups (upright 12.375 MPa, upright plus forward flexion 16.411 MPa, upright plus backward extension 16.801 MPa, upright plus left bending 13.425 MPa, upright plus right rotation 13.014 MPa), and the Von Mises stress in the group of bone cement does not contact with upper and lower endplates was the lowest.

Conclusion: The bone cement contact with both upper and lower endplates can effectively absorb and transfer the stress level brought by the load, reduce the stress level of cancellous bone, and reduce the possibility of refracture of the operative vertebral body.