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Biomechanical Investigation Between Rigid and Semirigid Posterolateral Fixation During Daily Activities: Geometrically Parametric Poroelastic Finite Element Analyses


doi: 10.3389/fbioe.2021.646079.


eCollection 2021.

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Mohammad Nikkhoo et al.


Front Bioeng Biotechnol.


.

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Abstract

While spinal fusion using rigid rods remains the gold standard treatment modality for various lumbar degenerative conditions, its adverse effects, including accelerated adjacent segment disease (ASD), are well known. In order to better understand the performance of semirigid constructs using polyetheretherketone (PEEK) in fixation surgeries, the objective of this study was to analyze the biomechanical performance of PEEK versus Ti rods using a geometrically patient-specific poroelastic finite element (FE) analyses. Ten subject-specific preoperative models were developed, and the validity of the models was evaluated with previous studies. Furthermore, FE models of those lumbar spines were regenerated based on postoperation images for posterolateral fixation at the L4-L5 level. Biomechanical responses for instrumented and adjacent intervertebral discs (IVDs) were analyzed and compared subjected to static and cyclic loading. The preoperative model results were well comparable with previous FE studies. The PEEK construct demonstrated a slightly increased range of motion (ROM) at the instrumented level, but decreased ROM at adjacent levels, as compared with the Ti. However, no significant changes were detected during axial rotation. During cyclic loading, disc height loss, fluid loss, axial stress, and collagen fiber strain in the adjacent IVDs were higher for the Ti construct when compared with the intact and PEEK models. Increased ROM, experienced stress in AF, and fiber strain at adjacent levels were observed for the Ti rod group compared with the intact and PEEK rod group, which can indicate the risk of ASD for rigid fixation. Similar to the aforementioned pattern, disc height loss and fluid loss were significantly higher at adjacent levels in the Ti rod group after cycling loading which alter the fluid-solid interaction of the adjacent IVDs. This phenomenon debilitates the damping quality, which results in disc disability in absorbing stress. Such finding may suggest the advantage of using a semirigid fixation system to decrease the chance of ASD.


Keywords:

PEEK; finite element analysis; personalized modeling; poroelastic; posterolateral fixation; spinal biomechanics; titanium.

Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures


FIGURE 1



FIGURE 1

(A) Procedure of personalized poroelastic finite element (FE) modeling of the lumbosacral spine and (B) preoperative (intact) and postoperative (posterolateral fixation) FE models.


FIGURE 2



FIGURE 2

Stress–strain properties of the ligaments for finite element modeling. ISL, interspinous ligament; ALL, anterior longitudinal ligament; PLL, posterior longitudinal ligament; SSL, supraspinous ligament; ITL, intertransverse ligament; LF, ligamentum flavum; CL, capsular ligament.


FIGURE 3



FIGURE 3

Loading scenario of the compressive force (flexion, extension, lateral bending, and axial rotation moments of 10 N m were applied at points 1 and 2).


FIGURE 4



FIGURE 4

Intersegmental range of motions (ROMs) for preoperative FE models compared with the numerical studies (Dreischarf et al., 2014) in (A) flexion, (B) extension, (C) lateral bending, and (D) axial rotation. The reported ROMs in lateral bending and axial rotation are the average in the left and right directions. The error bars indicate the ranges of the results.


FIGURE 5



FIGURE 5

Intradiscal pressure (IDP) for preoperative FE models compared with the numerical studies (Dreischarf et al., 2014) in (A) flexion, (B) extension, (C) lateral bending, and (D) axial rotation. The reported IDPs in lateral bending and axial rotation are the average in the left and right directions. The error bars indicate the ranges of the results.


FIGURE 6



FIGURE 6

Facet joint forces (FJF) for preoperative FE models compared with the numerical studies (Dreischarf et al., 2014) in (A) extension, (B) lateral bending, and (C) axial rotation. The reported FJFs in lateral bending and axial rotation are the average in the left and right directions. The error bars indicate the ranges of the results.


FIGURE 7



FIGURE 7

Intersegmental range of motions (ROMs) for postoperative FE models in the (A) instrumented level (L4–L5), (B) upper adjacent level (L3–L4), and (C) lower adjacent level (L5–S1). The error bars indicate the standard deviations, and “∗” shows that p values < 0.05.


FIGURE 8



FIGURE 8

Percentage of disc height loss and fluid loss for postoperative FE models in the (A) upper adjacent level (L3–L4) and (B) lower adjacent level (L5–S1). The error bars indicate the standard deviations, and “∗” shows that p values < 0.05.


FIGURE 9



FIGURE 9

Increased axial stress in annulus fibrosus (AF) for postoperative FE models in the (A) upper adjacent level (L3–L4) and (B) lower adjacent level (L5–S1) in different directions. The reported results in lateral bending and axial rotation are the average in left and right directions. The error bars indicate the standard deviations, and “∗” shows that p values < 0.05.


FIGURE 10



FIGURE 10

Increased fiber strain in annulus fibrosus (AF) for postoperative FE models in the (A) upper adjacent level (L3–L4) and (B) lower adjacent level (L5–S1) in different directions. The reported results in lateral bending and axial rotation are the average in the left and right directions. The error bars indicate the standard deviations, and “∗” shows that p values < 0.05.

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