DOI: https://doi.org/10.22141/1608-1706.2.20.2019.168024

Investigation of the design of posterior spondylodesis in the loss of support ability of the anterior complex of the thoracic and lumbar spine

V.O. Kutsenko, I.B. Timchenko, A.I. Popov, M.O. Korzh, V.O. Radchenko, Ya.M. Garaschenko, M.V. Lisak

Abstract


Background. The main causes of instability of the spinal column in patients with spinal tumors are pathological fractures and intervertebral defects after tumor resection. In this case, surgical stabilization is recommended by the authors, if the spine collapse exceeds 50 % of its height, if more than 50 % of the spine is affected, if there is a resorption of the pedicle of vertebral arch or an involvement of all the rear elements. The use of transpedicular devices ensures stable fixation and stability of the spine segments even with the destruction of all three columns. The purpose of the study: based on the mathematical modeling, to determine the optimal variants of posterior spondylodesis in the loss of the support ability of the anterior spine. Materials and methods. Mathematical modeling using finite element method of the variants of posterior spondylodesis design in case of the loss of the support ability of the anterior spine additionally includes tomograms, allocation of tissues of given density, creation of a triangulation model using the software package 3D Slicer. The problem of processing point clouds and obtaining a solid state model are covered. Results. The calculation of strength for various variants of attaching the spine fixation system during resection of L1, L2, and Th12 vertebras has been made, and the analysis of the calculation results has been carried out. Calculations have shown that the maximum tension in the tilt back position occurs in the complete resection of the three vertebrae with attachment to one adjacent body and accounts for 415 MPa, which significantly exceeds the strength of both cortical bone and the titanium. Minimum values of internal stresses by von Mises are observed in complete resection of one vertebra and fixing in three adjacent vertebrae. The stress did not exceed 24 MPa, which provides more than 10-fold safety factor. Conclusions. Results of the calculations showed that during resection of one vertebrae it is enough to fix one body, if two vertebrae are resected, fixation in three bodies is desirable, but it is possible to fix in two vertebrae with a threefold safety factor. In vertebrectomy of three vertebrae it is possible to fix only in three or more adjacent bodies. Physical models of human vertebras allow a surgeon to pre-make structures under the individual form of the patient’s vertebra, to plan their actions before surgery, which greatly reduces the time of surgery and blood loss. It also reduces the time required for the training of young surgeons, decreases the likelihood of errors during operations, and, accordingly, reduces the number of unsuccessful surgeries. This is especially important in the unique cases of the disease.

Keywords


spine; spondylodesis; pathological fracture; mathematical modeling

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