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Abstract
Study Design
Finite element models of the thoracolumbar spine with various techniques used in spinal fractures were developed to investigate the effects of fixation techniques on spinal stiffness.
Objectives
To develop finite element models of the thoracolumbar spine with various fixation techniques to compare their spinal stiffness characteristics.
Summary of Literature Review
Various anterior and posterior instrumentation options have been applied to stabilize unstable burst fractures of the thoracolumbar spines. The biomechanical effects of different instrumentation options on spinal stability are still unknown.
Materials and Methods
The 3-D finite element model of the human thoracolumbar spine (T12-L2) was reconstructed from CT images. Various anterior and posterior instrumentation techniques, 1-rod and 2-rod anterior fixations, anterior fixations with posterior fixation, and posterior fixation only, were virtually performed in the developed model with a long cage after corpectomy. Five loading cases, axial compression, flexion, extension, lateral bending, and torsion, were applied up to 1000 N and 10 Nm, respectively. The axial displacement and the rotations of T12 with respect to L2 were measured to analyze the stiffness of the spinal segments.
Results
The posterior fixation technique increased the stiffness of the spine the most. The addition of an anterior rod from 1 to 2 increased the stiffness significantly without posterior fixation, but little effect was found with posterior fixation. Among all fixation techniques, the inter-segmental stiffnesses were similar to those of the intact model in torsion cases. In the other loading cases, the inter-segmental stiffnesses were much greater than those of the intact models.
Conclusions
Finite element models of the thoracolumbar spine were developed with various fixation methods. The intact models were validated with in-vitro experimental tests. The posterior fixation technique had a more significant effect on spine stability than did anterior fixation. And anteroposterior fixation techniques provided increased spinal stiffness
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Fig. 1.
The finite element models of thoracolumbar spine segments with different anteroposterior fixation techniques were developed. (A) One-rod anterior fixation with posterior fixation (1R-M-P). (B) Two-rod anterior fixation with posteri-or fixation(2R-M-P). (C) Posterior fixation(0R-M-P).
Fig. 2.
The stiffness of 1 level intact model (Intact-1L) and 2 level intact mode l(Intact-2L) for flexion, extension, lateral bending, and torsion were validated with previous in-vitro experimental studies12-17).
Table 1.
The finite element analysis results showed that the stiffness with various fixation instrumentations were changed in flexion, extension, and lateral bending cased compared with those in the intact model (Nm/)
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