Tether pre-tension within vertebral body tethering reduces motion of the spine and influences coupled motion: a finite element analysis

Luis Fernando Nicolini; Rafael Carreira Oliveira; Marx Ribeiro; Marcus Stoffel; Bernd Markert; Philipp Kobbe; Frank Hildebrand; Per Trobisch; Marcelo Simoni Simões; Carlos Rodrigo de Mello Roesler; Eduardo Alberto Fancello

doi:10.1016/j.compbiomed.2023.107851

Tether pre-tension within vertebral body tethering reduces motion of the spine and influences coupled motion: a finite element analysis

Comput Biol Med. 2024 Feb:169:107851. doi: 10.1016/j.compbiomed.2023.107851. Epub 2023 Dec 14.

Affiliations

¹ Group of Analysis and Mechanical Design - GRANTE, Dep. of Mechanical Engineering, Federal University of Santa Catarina, Brazil; Mechanical and Aerospace Technology Laboratory (NUMAE), Dep. of Mechanical Engineering, Federal University of Santa Maria, Brazil. Electronic address: nicolini.luis@ufsm.br.
² Group of Analysis and Mechanical Design - GRANTE, Dep. of Mechanical Engineering, Federal University of Santa Catarina, Brazil.
³ Group of Analysis and Mechanical Design - GRANTE, Dep. of Mechanical Engineering, Federal University of Santa Catarina, Brazil; Department of Orthopedics, Trauma and Reconstructive Surgery, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany.
⁴ Institute of General Mechanics (IAM), RWTH Aachen University, Germany.
⁵ Department of Orthopedics, Trauma and Reconstructive Surgery, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany.
⁶ Eifelklinik St. Brigida, Simmerath, Germany.
⁷ Biomechanical Engineering Laboratory - LEBm, Dep. of Mechanical Engineering, Federal University of Santa Catarina, Brazil.
⁸ Group of Analysis and Mechanical Design - GRANTE, Dep. of Mechanical Engineering, Federal University of Santa Catarina, Brazil; Biomechanical Engineering Laboratory - LEBm, Dep. of Mechanical Engineering, Federal University of Santa Catarina, Brazil.

PMID: 38113683
DOI: 10.1016/j.compbiomed.2023.107851

Abstract

Anterior Vertebral Body Tethering (VBT) is a novel fusionless treatment option for selected adolescent idiopathic scoliosis patients which is gaining widespread interest. The primary objective of this study is to investigate the effects of tether pre-tension within VBT on the biomechanics of the spine including sagittal and transverse parameters as well as primary motion, coupled motion, and stresses acting on the L2 superior endplate. For that purpose, we used a calibrated and validated Finite Element model of the L1-L2 spine. The VBT instrumentation was inserted on the left side of the L1-L2 segment with different cord pre-tensions and submitted to an external pure moment of 6 Nm in different directions. The range of motion (ROM) for the instrumented spine was measured from the initial post-VBT position. The magnitudes of the ROM of the native spine and VBT-instrumented with pre-tensions of 100 N, 200 N, and 300 N were, respectively, 3.29°, 2.35°, 1.90° and 1.61° in extension, 3.30°, 3.46°, 2.79°, and 2.17° in flexion, 2.11°, 1.67°, 1.33° and 1.06° in right axial rotation, and 2.10°, 1.88°, 1.48° and 1.16° in left axial rotation. During flexion-extension, an insignificant coupled lateral bending motion was observed in the native spine. However, VBT instrumentation with pre-tensions of 100 N, 200 N, and 300 N generated coupled right lateral bending of 0.85°, 0.81°, and 0.71° during extension and coupled left lateral bending of 0.32°, 0.24°, and 0.19° during flexion, respectively. During lateral bending, a coupled extension motion of 0.33-0.40° is observed in the native spine, but VBT instrumentation with pre-tensions of 100 N, 200 N, and 300 N generates coupled flexion of 0.67°, 0.58°, and 0.42° during left (side of the implant) lateral bending and coupled extension of 1.28°, 1.07°, and 0.87° during right lateral bending, respectively. Therefore, vertebral body tethering generates coupled motion. Tether pre-tension within vertebral body tethering reduces the motion of the spine.

Keywords: Curve correction; Finite element method; Fusionless; Growth modulation; Scoliosis; Spine; Vertebral body tethering.

MeSH terms

Adolescent
Biomechanical Phenomena
Finite Element Analysis
Humans
Lumbar Vertebrae
Range of Motion, Articular
Rotation
Scoliosis*
Spine
Vertebral Body*