Development of a Computer-Aided Design and Finite Element Analysis Combined Method for Affordable Spine Surgical Navigation With 3D-Printed Customized Template

Peter Endre Eltes; Marton Bartos; Benjamin Hajnal; Agoston Jakab Pokorni; Laszlo Kiss; Damien Lacroix; Peter Pal Varga; Aron Lazary

doi:10.3389/fsurg.2020.583386

Development of a Computer-Aided Design and Finite Element Analysis Combined Method for Affordable Spine Surgical Navigation With 3D-Printed Customized Template

Front Surg. 2021 Jan 25:7:583386. doi: 10.3389/fsurg.2020.583386. eCollection 2020.

Authors

Peter Endre Eltes^{1

2

3}, Marton Bartos⁴, Benjamin Hajnal², Agoston Jakab Pokorni², Laszlo Kiss^{1

2

3}, Damien Lacroix⁵, Peter Pal Varga¹, Aron Lazary^{1

6}

Affiliations

¹ National Center for Spinal Disorders, Buda Health Center, Budapest, Hungary.
² In Silico Biomechanics Laboratory, National Center for Spinal Disorders, Buda Health Center, Budapest, Hungary.
³ School of Ph.D. Studies, Semmelweis University, Budapest, Hungary.
⁴ Do3D Innovations Ltd., Budapest, Hungary.
⁵ Department of Mechanical Engineering, INSIGNEO Institute for In Silico Medicine, The University of Sheffield, Sheffield, United Kingdom.
⁶ Department of Spinal Surgery, Semmelweis University, Budapest, Hungary.

Abstract

Introduction: Revision surgery of a previous lumbosacral non-union is highly challenging, especially in case of complications, such as a broken screw at the first sacral level (S1). Here, we propose the implementation of a new method based on the CT scan of a clinical case using 3D reconstruction, combined with finite element analysis (FEA), computer-assisted design (CAD), and 3D-printing technology to provide accurate surgical navigation to aid the surgeon in performing the optimal surgical technique by inserting a pedicle screw at the S1 level. Materials and Methods: A step-by-step approach was developed and performed as follows: (1) Quantitative CT based patient-specific FE model of the sacrum was created. (2) The CAD model of the pedicle screw was inserted into the sacrum model in a bicortical convergent and a monocortical divergent position, by overcoming the geometrical difficulty caused by the broken screw. (3) Static FEAs (Abaqus, Dassault Systemes) were performed using 500 N tensile load applied to the screw head. (4) A template with two screw guiding structures for the sacrum was designed and manufactured using CAD design and 3D-printing technologies, and investment casting. (5) The proposed surgical technique was performed on the patient-specific physical model created with the FDM printing technology. The patient-specific model was CT scanned and a comparison with the virtual plan was performed to evaluate the template accuracy Results: FEA results proved that the modified bicortical convergent insertion is stiffer (6,617.23 N/mm) compared to monocortical divergent placement (2,989.07 N/mm). The final template was created via investment casting from cobalt-chrome. The template design concept was shown to be accurate (grade A, Gertzbein-Robbins scale) based on the comparison of the simulated surgery using the patient-specific physical model and the 3D virtual surgical plan. Conclusion: Compared to the conventional surgical navigation techniques, the presented method allows the consideration of the patient-specific biomechanical parameters; is more affordable, and the intraoperative X-ray exposure can be reduced. This new patient- and condition-specific approach may be widely used in revision spine surgeries or in challenging primary cases after its further clinical validation.

Keywords: 3D printing; computed tomography; finite element simulation; navigation; spine surgery; surgical guidance/navigation.