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. 2022 Jan 17;5(1):172-182.
doi: 10.1021/acsabm.1c01027. Epub 2021 Dec 14.

Finite Element Analysis of a Bionate Ring-Shaped Customized Lumbar Disc Nucleus Prosthesis

Amparo Vanaclocha-Saiz  1 , Vicente Vanaclocha  2 , Carlos M Atienza  3   4 , Pablo Clavel  5 , Pablo Jorda-Gomez  6 , Carlos Barrios  7 , Leyre Vanaclocha  8
Affiliations

Finite Element Analysis of a Bionate Ring-Shaped Customized Lumbar Disc Nucleus Prosthesis

Amparo Vanaclocha-Saiz et al. ACS Appl Bio Mater. .

Abstract

Study design: Biomechanical study of a nucleus replacement with a finite element model. Objective: To validate a Bionate 80A ring-shaped nucleus replacement. Methods: The ANSYS lumbar spine model made from lumbar spine X-rays and magnetic resonance images obtained from cadaveric spine specimens were used. All materials were assumed homogeneous, isotropic, and linearly elastic. We studied three options: intact spine, nucleotomy, and nucleus implant. Two loading conditions were evaluated at L3-L4, L4-L5, and L5-S1 discs: a 1000 N axial compression load and this load after the addition of 8 Nm flexion moment in the sagittal plane plus 8 Nm axial rotation torque. Results: Maximum nucleus implant axial compression stresses in the range of 16-34 MPa and tensile stress in the range of 5-16 MPa, below Bionate 80A resistance were obtained. Therefore, there is little risk of permanent implant deformation or severe damage under normal loading conditions. Nucleotomy increased segment mobility, zygapophyseal joint and end plate pressures, and annulus stresses and strains. All these parameters were restored satisfactorily by nucleus replacement but never reached the intact status. In addition, annulus stresses and strains were lower with the nucleus implant than in the intact spine under axial compression and higher under complex loading conditions. Conclusions: Under normal loading conditions, there is a negligible risk of nucleus replacement, permanent deformation or severe damage. Nucleotomy increased segmental mobility, zygapophyseal joint pressures, and annulus stresses and strains. Nucleus replacement restored segmental mobility and zygapophyseal joint pressures close to the intact spine. End plate pressures were similar for the intact and nucleus implant conditions under both loading modes. Manufacturing customized nucleus implants is considered feasible, as satisfactory biomechanical performance is confirmed.

Keywords: degenerative disc disease; disc hernia; finite element model; motion preservation; nucleus disc replacement; polycarbonate urethane.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Above, the process for customization and generation of lumbar spine FEM. Below, different disc model configurations were obtained with the CAD software (SolidWorks).
Figure 2
Figure 2
Finite element model process.
Figure 3
Figure 3
Annulus inner stresses and strains in the L3-L4 disc after nucleus replacement.
Figure 4
Figure 4
L3-L4 facet joint and end plate pressures and upper vertebra vertical displacement.
Figure 5
Figure 5
Annulus inner stresses and strains in the L4-L5 disc after nucleus replacement.
Figure 6
Figure 6
L4-L5 facet joint and end plate pressures and upper vertebra vertical displacement.
Figure 7
Figure 7
Annulus inner stresses and strains in the L5-S1 disc after nucleus replacement.
Figure 8
Figure 8
L5-S1 facet joint and end plate pressures and upper vertebra vertical displacement.
See this image and copyright information in PMC

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