Use of computer techniques in the development of vertebral implants for posterior spinal fusion of the thoracic spine
Background. Surgery of the spine requires a regular re-interpretation of approaches to the selection of new materials used in surgical interventions. In case of vertebrectomy, mainly titanium implants are used, both for posterior spine fusion and for interbody fusion. Oncological control is performed not only by laboratory methods, but also by CT, MRI. Therefore, implants, in addition to the durability and biocompatibility characteristics, must meet the above requirements in MRI and CT study. The method of vertebrectomy “en blok” by Tomita allows the use of transpedicular fixation and interbody spinal alignment with posterior access. But according to the literature data, migration or prolongation of the titanium intercostal implant in adjacent vertebral bodies occurs in 9.5 % of cases. The purpose was to solve the problem of migration of an intercostal implant in thoracic vertebrectomy with posterior access using new structural solutions. Materials and methods. A model of the human pectoral pillar was created, which takes into account all the forces that they cause and places of application of these forces. The total number of photos of the spine of the 1st patient is 260, divided into 12 groups, each of which has an average of 35–40 photos. Particular attention was paid to the places of contact between the vertebrae and the transition of the vertebral body to its posterior part. Correct mutual arrangement of the vertebrae was provided by the imaging tomography, which were divided into groups according to the specific vertebrae. Results. The best adhesion of the implant to the surface of the adjacent vertebrae is provided by riveting. The connection of the carbon cylinder and rod was carried out with the help of a titanium rod of variable shape, such construction allowed provide the minimum stresses and evenly distribute them throughout the structure. In order to prevent the unscrewing of the nut, it is proposed to make a thread with a tension, which in the future concentrates the maximum stresses in this place, but is available not exceeding 10 % of the strength of the specified material. Application of such construction allowed minimize the use of titanium in these operations and partially replace it with CCC (carbon-carbon composite). For titanium alloys, used in the developed constructions, permissible load is at average 600 MPa, the highest voltage value is 163 MPa. The maximum operating voltages are 20.318 MPa for metal structures and 1.1288 MPa
for HVC elements. Three kits of implants with minimum, average and maximum diameters and relative “dependent” sizes were crea-ted. Conclusions. The results of mathematical modeling demonstra-ted that it is possible and grounded to use carbon-based materials, namely CCC. This article presents a sample of the implant construction made from the specified material, as well as a design solution that allows solving the problem of fixing the implant in the spine, that makes it easier to perform the operation. Simulated technology for obtaining a component with the most complex design in the deve-loped assembly — the chapter “Endoprosthesis”.
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