Mathematical modeling of variants of thoracolumbar junction transpedicular fixation after resection of Th12 vertebra under compressive load

Abstract

Background. The area of the thoracolumbar junction is characterized by a significant load that dictates increased requirements to stabilization, which should not only provide a reliable and rigid fixation, but also ensure the maximum uniform distribution of the load on all elements of both the metal structure and the bone tissue to exclude the failure of fixation in the long run. Purpose of the study is to investigate the influence of the transpedicular screw length and the presence of crosslinks on the load distribution during surgical resection of one vertebra from the thoracolumbar junction under the influence of axial compressive load. Materials and methods. We analyzed mathematical finite-element model of the part of thoracolumbar spine (Th9-L5), where the Th12 vertebra was removed and replaced by an interbody implant with additional fixation by a transpedicular system. Four variants of transpedicular fixation were modeled using short and long screws, as well as with and without two crosslinks. The stress-strain state of the models was studied under the influence of a vertical compressive distributed load of 350 N. Results. When using short screws and in the absence of crosslinks, the maximum stresses in the Th10, Th11, L1, and L2 vertebrae are 7.2, 5.3, 4.2, and 14.3 MPa, respectively, when using long screws without crosslinks — 6.5, 4.6, 3.8 and 13.5 MPa. The model with short screws and crosslinks shows 7.1, 4.4, 3.9 and 14.0 MPa, while the application of long screws with crosslinks is 6.3, 4.5, 3.5 and 13.2 MPa, respectively. Conclusions. With a compressive load, the use of long screws allows to reduce the level of stress in the bone elements of the models, the use of crosslinks provides greater rigidity to the posterior support of the transpedicular structure, which leads to an increase in stress on the fixing screws but allows to reduce the level of stress in the bone tissue.