# Modeling the Effect of Annulus Fibrosus Stiffness on the Stressed State of a Vertebral L1 Body and Nucleus Pulposus

## TL;DR

This paper studies how the stiffness of spinal discs affects the strength of the L1 vertebra under stress.

## Contribution

A new computational model links annulus fibrosus stiffness to vertebral body stress responses.

## Key findings

- Increased annulus fibrosus stiffness reduces the vertebral body's ability to withstand external loading.
- A degenerative disc led to vertebral yielding at 6 mm displacement, while healthy discs showed 20% higher strength.
- The model can help evaluate disc health and predict spinal system behavior.

## Abstract

The investigation examines the transference of stiffness from intervertebral discs (IVDs) to the lumbar body of the L1 vertebra and the interactions among adjacent tissues. A computational model of the vertebra was developed, considering parameters such as cortical bone thickness, trabecular bone elasticity, and the nonlinear response of the nucleus pulposus to external loading. A nonlinear dynamic analysis was performed, revealing certain trends: a heightened stiffness of the annulus fibrosus correlates with a significant reduction in the vertebral body’s ability to withstand external loading. At a supplied displacement of 6 mm, the vertebra with a degenerative disc reached its yielding point, whereas the vertebrae with a healthy annulus fibrosus exhibited a strength capacity exceeding 20%. The obtained findings and proposed methodology are potentially useful for biomedical engineers and clinical specialists in evaluating the condition of the annulus fibrosus and predicting its influence on the bone components of the spinal system.