Bone density optimized pedicle screw insertion

Christos Tsagkaris; Anna-Katharina Calek; Marie-Rosa Fasser; José Miguel Spirig; Sebastiano Caprara; Mazda Farshad; Jonas Widmer

doi:10.3389/fbioe.2023.1270522

Bone density optimized pedicle screw insertion

Front Bioeng Biotechnol. 2023 Oct 26:11:1270522. doi: 10.3389/fbioe.2023.1270522. eCollection 2023.

Authors

Christos Tsagkaris¹, Anna-Katharina Calek^{1

2}, Marie-Rosa Fasser^{2

3}, José Miguel Spirig⁴, Sebastiano Caprara^{2

3}, Mazda Farshad^{1

4}, Jonas Widmer^{2

3}

Affiliations

¹ Department of Orthopedics, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.
² Spine Biomechanics, Department of Orthopedic Surgery, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.
³ Institute for Biomechanics, ETH Zurich, Zurich, Switzerland.
⁴ University Spine Center Zurich, Balgrist University Hospital, University of Zurich, Zurich, Switzerland.

Abstract

Background: Spinal fusion is the most common surgical treatment for the management of degenerative spinal disease. However, complications such as screw loosening lead to painful pseudoarthrosis, and are a common reason for revision. Optimization of screw trajectories to increase implant resistance to mechanical loading is essential. A recent optimization method has shown potential for determining optimal screw position and size based on areas of high bone elastic modulus (E-modulus). Aim: The aim of this biomechanical study was to verify the optimization algorithm for pedicle screw placement in a cadaveric study and to quantify the effect of optimization. The pull-out strength of pedicle screws with an optimized trajectory was compared to that of a traditional trajectory. Methods: Twenty-five lumbar vertebrae were instrumented with pedicle screws (on one side, the pedicle screws were inserted in the traditional way, on the other side, the screws were inserted using an optimized trajectory). Results: An improvement in pull-out strength and pull-out strain energy of the optimized screw trajectory compared to the traditional screw trajectory was only observed for E-modulus values greater than 3500 MPa cm³. For values of 3500 MPa cm³ or less, optimization showed no clear benefit. The median screw length of the optimized pedicle screws was significantly smaller than the median screw length of the traditionally inserted pedicle screws, p < 0.001. Discussion: Optimization of the pedicle screw trajectory is feasible, but seems to apply only to vertebrae with very high E-modulus values. This is likely because screw trajectory optimization resulted in a reduction in screw length and therefore a reduction in the implant-bone interface. Future efforts to predict the optimal pedicle screw trajectory should include screw length as a critical component of potential stability.

Keywords: pedicle screw; spine; spine biomechanics; surgical planning; trajectory.

Grants and funding

The author(s) declare financial support was received for the research, authorship, and/or publication of this article. The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article. This work was supported by the Olga Mayenfisch Stiftung, Zurich.