Study of the Stress-Strain State of the "Spine-Implant" System in Different Types of Tumor Lesions

Lesions resulting from the oncological process disrupt the structural stability of the spine and lead to pathological fractures and compression of the spinal cord structures. Surgical interventions used for spinal neoplasms can be both palliative and radical. Any of these surgical procedures significantly changes the biomechanical conditions of the spine functioning, and the wrong choice of surgical tactics can lead to fatal errors. The purpose of the study was to investigate the stress-strain state of the spine and the "spine-implant" system in various types of tumor lesions before and after stabilization surgical interventions. Material and methods. The model was built in the SolidWorks software. The calculations based on the finite element method and the analysis of the results were carried out in the ANSYS Workbench program. In the course of the study, a comparison was made between the character of stress-strain state distribution in the intact model and in models where the following changes were modeled: lesion of the T12 vertebral body by a tumor process by 30% of its volume (model 1) and cement augmentation of the created defect (model 2), and also lesions of the vertebral body by 60% with concomitant local kyphosis L5 (model 3) and stabilization with a transpedicular construction T10-L2 (model 4). Results and discussion. Based on the results of the calculations, it was determined that the presence of a T12 vertebral body defect by up to 30% leads to an increase in the absolute values of stresses in the vertebral body and the posterior supporting complex, while cement augmentation leads to the restoration of stress values close to the intact spine. Consequently, the presence of a pathological lesion in the vertebral body, occupying up to 60% of its volume, leads to disturbances in the supporting function of not only the affected segment, but also the segments adjacent to it. Placement of a transpedicular implant and restoration of the support of the anterior column of the affected vertebra makes it possible to bring the state of load distribution of the affected area of the spine closer to normal values. Conclusion. The study of the stress-strain state of the "spine-implant" system in the presence of a pathological lesion occupying 30% of the volume of the vertebral body leads to a violation of the supporting function of the affected vertebra, and an increase in the defect to 60% of the volume of the vertebral body and the presence of local kyphotic deformity of the spine negatively affects the distribution stresses in the segments that are adjacent to it. The use of cement augmentation and transpedicular construction allows the support function of the spine to be restored in accordance with normal parameters of load distribution. Indications for the use of cement vertebroplasty is the presence of a defect up to 30% of the volume of the vertebral body. In the case of the volume increase of the vertebra defect up to 60% and the occurrence of kyphotic deformity, it is necessary to supplement the cement vertebroplasty with transpedicular fixation of the spine