The Effect of the TiO2 Anodization Layer in Pedicle Screw Conductivity: An Analytical, Numerical, and Experimental Approach
Bioengineering, 2024
The Effect of the TiO2 Anodization Layer in Pedicle Screw Conductivity: An Analytical, Numerical, and Experimental Approach
Pedro Fonseca 1,2,3,* , Márcio Fagundes Goethel 1,3 , João Paulo Vilas-Boas 1,3,4 , Manuel Gutierres 1,5 and Miguel Velhote Correia 1,2,6
1 Porto Biomechanics Laboratory, Faculty of Sports, University of Porto, 4200-450 Porto, Portugal
2 Faculty of Engineering, University of Porto, 4200-465 Porto, Portugal
3 Faculty of Sports, University of Porto, 4200-450 Porto, Portugal
4 Centre of Research, Education, Innovation and Intervention in Sport, Faculty of Sport, University of Porto, 4200-450 Porto, Portugal
5 Faculty of Medicine, University of Porto, 4200-319 Porto, Portugal
6 Institute for Systems and Computer Engineering, Technology and Science, 4200-465 Porto, Portugal
* Correspondence: pedro.labiomep@fade.up.pt
Abstract:
The electrical stimulation of pedicle screws is a technique used to ensure its correct placement within the vertebrae pedicle. Several authors have studied these screws’ electrical properties with the objective of understanding if they are a potential source of false negatives. As titanium screws are anodized with different thicknesses of a high electrical resistance oxide (TiO2), this study investigated, using analytical, numerical, and experimental methods, how its thickness may affect pedicle screw’s resistance and conductivity. Analytical results have demonstrated that the thickness of the TiO2 layer does result in a significant radial resistance increase (44.21 mΩ/nm, for Ø 4.5 mm), and a decrease of conductivity with layers thicker than 150 nm. The numerical approach denotes that the geometry of the screw further results in a decrease in the pedicle screw conductivity, especially after 125 nm. Additionally, the experimental results demonstrate that there is indeed an effective decrease in conductivity with an increase in the TiO2 layer thickness, which is also reflected in the screw’s total resistance. While the magnitude of the resistance associated with each TiO2 layer thickness may not be enough to compromise the ability to use anodized pedicle screws with a high-voltage electrical stimulator, pedicle screws should be the subject of more frequent electrical characterisation studies.
The electrical stimulation of pedicle screws is a technique used to ensure its correct placement within the vertebrae pedicle. Several authors have studied these screws’ electrical properties with the objective of understanding if they are a potential source of false negatives. As titanium screws are anodized with different thicknesses of a high electrical resistance oxide (TiO2), this study investigated, using analytical, numerical, and experimental methods, how its thickness may affect pedicle screw’s resistance and conductivity. Analytical results have demonstrated that the thickness of the TiO2 layer does result in a significant radial resistance increase (44.21 mΩ/nm, for Ø 4.5 mm), and a decrease of conductivity with layers thicker than 150 nm. The numerical approach denotes that the geometry of the screw further results in a decrease in the pedicle screw conductivity, especially after 125 nm. Additionally, the experimental results demonstrate that there is indeed an effective decrease in conductivity with an increase in the TiO2 layer thickness, which is also reflected in the screw’s total resistance. While the magnitude of the resistance associated with each TiO2 layer thickness may not be enough to compromise the ability to use anodized pedicle screws with a high-voltage electrical stimulator, pedicle screws should be the subject of more frequent electrical characterisation studies.
Keywords:
neuromonitoring; pedicle screw; electrical resistance; conductivity; oxide layer
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