Case-specific non-linear finite element models to predict failure behavior in two functional spinal units | JoVE Visualize

Area of Science:

Biomechanics and Computational Modeling
Spinal Fusion and Degeneration Research
Orthopaedic Surgery and Biomaterials

Background:

Current finite element (FE) models for predicting spinal failure typically focus on single vertebrae, omitting crucial posterior elements and intervertebral discs.
This limitation hinders the clinical relevance and accuracy of existing biomechanical models for spinal injury and treatment planning.

Purpose of the Study:

To develop and validate a case-specific, non-linear finite element (FE) model of two functional spinal units (FSUs) to predict spinal failure behavior.
To assess the model's ability to predict the failing vertebra, specimen deformation, stiffness, and load to failure.
To investigate the influence of different bone density-mechanical properties relationships (material models) on failure prediction accuracy.

Main Methods:

Twelve FSUs (T6-T8, T9-T11, T12-L2, L3-L5) with and without artificial metastases were subjected to destructive axial compression testing.
CT-based, case-specific non-linear FE models were created to simulate the experimental conditions.
Four commonly used material models were implemented to assign bone mechanical properties, and their impact on predictions was analyzed.

Main Results:

The FE model successfully identified the failing vertebra in 10 out of 11 specimens, demonstrating good predictive capability for fracture location.
Predictions of three-dimensional specimen deformations were less accurate.
While the model accurately predicted construct stiffness (R² = 0.637-0.688, p < 0.01), correlations between predicted and experimental load to failure were weak (R² = 0.219-0.247, p > 0.05).
The choice of material model significantly impacted stiffness predictions but had a minimal effect on fracture load predictions.

Conclusions:

The developed FE models show promise in identifying the weakest vertebra within a functional spinal unit, aiding in understanding failure mechanisms.
Significant advancements are necessary to improve the accuracy of predicting in vivo failure loads using current FE modeling techniques.
Further research should focus on refining material models and incorporating additional anatomical features to enhance the predictive power of FE models for spinal failure.