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Comparative Study
. 2013 Oct 2:14:281.
doi: 10.1186/1471-2474-14-281.

Biomechanical comparison of three stand-alone lumbar cages--a three-dimensional finite element analysis

Shih-Hao Chen  1 , Ming-Chieh Chiang, Jin-Fu Lin, Shang-Chih Lin, Ching-Hua Hung
Affiliations
Comparative Study

Biomechanical comparison of three stand-alone lumbar cages--a three-dimensional finite element analysis

Shih-Hao Chen et al. BMC Musculoskelet Disord. .

Abstract

Background: For anterior lumbar interbody fusion (ALIF), stand-alone cages can be supplemented with vertebral plate, locking screws, or threaded cylinder to avoid the use of posterior fixation. Intuitively, the plate, screw, and cylinder aim to be embedded into the vertebral bodies to effectively immobilize the cage itself. The kinematic and mechanical effects of these integrated components on the lumbar construct have not been extensively studied. A nonlinearly lumbar finite-element model was developed and validated to investigate the biomechanical differences between three stand-alone (Latero, SynFix, and Stabilis) and SynCage-Open plus transpedicular fixation. All four cages were instrumented at the L3-4 level.

Methods: The lumbar models were subjected to the follower load along the lumbar column and the moment at the lumbar top to produce flexion (FL), extension (EX), left/right lateral bending (LLB, RLB), and left/right axial rotation (LAR, RAR). A 10 Nm moment was applied to obtain the six physiological motions in all models. The comparison indices included disc range of motion (ROM), facet contact force, and stresses of the annulus and implants.

Results: At the surgical level, the SynCage-open model supplemented with transpedicular fixation decreased ROM (>76%) greatly; while the SynFix model decreased ROM 56-72%, the Latero model decreased ROM 36-91%, in all motions as compared with the INT model. However, the Stabilis model decreased ROM slightly in extension (11%), lateral bending (21%), and axial rotation (34%). At the adjacent levels, there were no obvious differences in ROM and annulus stress among all instrumented models.

Conclusions: ALIF instrumentation with the Latero or SynFix cage provides an acceptable stability for clinical use without the requirement of additional posterior fixation. However, the Stabilis cage is not favored in extension and lateral bending because of insufficient stabilization.

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Figures

Figure 1
Figure 1
Front and side views of the four ALIF cages were used in this study. (A) Latero. (B) SynFix. (C) Stabilis. (D) SynCage-Open.
Figure 2
Figure 2
The lumbar finite-element model used in this study. (A) Intact model from L1 to L5 levels. (B) Instrumented model at the L3-4 level. (C) Four ALIF cages instrumented at the L3-4 level.
Figure 3
Figure 3
Comparison of the normalized intersegmental ROM among all models under six motions. (A) Surgical level.(B-C) Adjacent levels.
Figure 4
Figure 4
Stress comparison of the normalized stress among all models under six motions. (A) Annulus stress. (B) Implant stress.
Figure 5
Figure 5
Stress distribution of the ground substance at the surgical level for all models. (A) Extension (B) Left lateral bending. (C) Right lateral bending.
Figure 6
Figure 6
Comparison of facet contact force among all models. (A) Extension. (B) Left axial rotation. (C) Right axial rotation. Middle bars are the surgical level (L3-4); left and right bars are the adjacent levels (L2-3 and L4-5).
Figure 7
Figure 7
Distribution of implant stress for the Latero, SynFix, and Stabilis models. (A) Extension. (B) Left lateral bending.(C) Right lateral bending.
Figure 8
Figure 8
Distribution of endplate stress on the upper surface of the L4 vertebra for all models. (A) Flexion. (B) Extension. (C) Left lateral bending. (D) Left axial rotation.
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