Comprehensive analysis of damage evolution in human annulus fibrosus: Numerical exploration of mechanical sensitivity to biological age-dependent alteration

Background and objective

The annulus fibrosus is an essential part of the intervertebral disc, critical for its structural integrity. Mechanical deterioration in this component can lead to complete disc failure, particularly through tears development, with radial tears being the most common. These tears are often the result of both mechanical and biological factors. This study aims to numerically investigate the mechanisms of radial failure in the annulus tissue, taking into account the mechanical and age-dependent biological damage origins. A newly developed microstructure-based model was upgraded to predict damage evolution in the different annulus regions.

Methods

The study employs a computational model to predict mechanical failures in various annulus regions, using experimental data for comparison. The model incorporates age-dependent microstructural changes to evaluate the effects of biological aging on the mechanical behavior. It specifically includes a detailed analysis of the temporal changes in circumferential rigidity and failure strain of the annulus.

Results

The model demonstrated a strong ability to replicate the experimental responses of the different annulus regions to failure. It revealed that age-related microstructural changes significantly impact the rigidity and failure response of the annulus, particularly in the posterior regions and as well the anterior inner side. These changes increase susceptibility to rupture with aging. A correlation was also observed between the composition of collagen fibers, water content, and the annulus transversal response in both radial and axial directions.

Conclusion

The findings challenge previous assumptions, showing that age-dependent microstructural changes have a notable effect on the annulus mechanical properties. The computational model closely aligns with experimental observations, underscoring the determinant role of oriented collagen fibers in radial failure. This study enhances the understanding of annulus failure and provides a foundation for further research on the impact of aging on disc mechanical integrity and failure.