# Experimental evaluation and constitutive modelling of cervical spine ligaments under low and high strain rates

## TL;DR

This study examines how four cervical spine ligaments behave under different strain rates and finds that stiffness and strength increase with age and high strain rates.

## Contribution

A new visco-hyperelastic model is proposed to capture ligament behavior under varying strain rates and age-related changes.

## Key findings

- PLL, LF, and CL show increased stiffness and elastic modulus under high-strain rates.
- Failure force increases only for PLL and LF at high strain rates.
- Age negatively affects mechanical parameters, highlighting the need for age-matched data.

## Abstract

In the paper the mechanical behavior under low (0.5 s⁻¹) and high-strain rate (50 s⁻¹) of four human cervical spine ligaments, anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL), ligamentum flava (LF), and capsular ligament (CL), harvested from elderly donors (70–90 years) is investigated. Results highlight that the PLL, LF, and CL exhibit statistically significant increases in stiffness and elastic modulus under high-strain loading. An increase in the failure force was observed only for the PLL and LF at 50 s⁻¹. Meta-regression analyses revealed that age exerts a negative influence on certain mechanical parameters, emphasizing the need for age-matched biomechanical data in both clinical and computational studies. A visco-hyperelastic constitutive model was fitted to the experimental stress-stretch curves, capturing both low-strain and high-strain rate responses with high goodness-of-fit metrics. Presented results advance understanding of ligament mechanics in older populations and offer valuable data for improving mathematical models aimed at injury prediction, particularly for high-impact events.