Análise da distribuição de cimento ósseo à base de PMMA em vértebras através de parafusos pediculares: modelagem e simulação.

Abstract

As the population's life expectancy increases, there are more and more health complications related to ageing, such as osteoporosis. Among the complications of osteoporosis are spinal fractures. In some cases, pedicle screws are used to stabilise the spine. However, when screws are inserted into bone that has been weakened by osteoporosis, the screw may not hold properly. In order to reduce this problem, a procedure called vertebroplasty is used. It consists of injecting bone cement into the vertebral body as a way of ensuring a better stabilisation of the screws. One of the main complications of this procedure is related to the cement leaking out of the vertebral body, causing various health problems. A literature survey revealed a lack of studies on the distribution of PMMA through pedicle screws in vertebrae using Computational Fluid Dynamics (CFD). In addition, the risks of cement leakage could be reduced and the vertebroplasty process optimised by using CFD to analyse the distribution of bone cement in the vertebra. Therefore, the purpose of this study is to evaluate, using CFD, the fluid-dynamic behaviour of PMMA-based bone cement injected into vertebrae via pedicle screws. The simulations performed considered laminar and incompressible flow regimes, constant physical chemical properties of the fluids and isotropic conditions for the porosity distribution and the permeability of the vertebra (porous medium). The commercial software Ansys FLUENT 2021 R2 was used to study the flow of cement inside the vertebra. The equations for the conservation of mass and linear momentum in the transient regime were solved using the Eulerian-Eulerian approach together with the Volume of Fluid (VOF) model. Different numerical meshes were generated and the Mesh Convergence Index (ICM) was used to assess the quality and independence of the results in relation to the computational mesh used. The factors influencing the distribution of bone cement were evaluated and compared with results reported in the literature, showing good agreement with each other. The numerical results indicate that the use of fenestrated pedicle screws can improve the stability of screw fixation and reduce the risk of bone cement leakage.