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

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.