Effect of Neck Muscle Strength and Passive Cervical Viscoelasticity on Regional Brain and Axonal Tissue Response

Abstract

This study evaluated how neck muscle strength and passive cervical viscoelasticity influence global brain motion, intracranial pressure, and regional predicted axonal strain during rapid head loading. An MRI-derived human head-neck finite element model with 5000 diffusion-derived axonal tracts represented by 90,692 embedded beam elements was evaluated using a 4 by 4 factorial design, with four levels each of muscle strength and passive ligament/disc viscoelasticity. The 16 cervical configurations were simulated under a 15 g acceleration-driven inertial load and a 7000 N frontal impact, resulting in 32 simulations. Increasing muscle strength from S25 to S95 at the reference passive-viscoelasticity level reduced mean regional 95th-percentile predicted axonal strain by 22% under inertial loading and 18% under frontal loading, with regional reductions ranging from 10% to 58% and 7% to 31%, respectively. Increasing passive cervical viscoelasticity from D25 to D95 at the reference strength level produced larger reductions in mean regional axonal strain of 35% and 33%, with regional reductions ranging from 14% to 70% and 16% to 56%. Passive viscoelasticity also reduced brain center-of-mass angular acceleration by 16% and 13%, compared with reductions of only 1% and 2% with increased muscle strength. Regional intracranial pressure decreased by 9%~21% under inertial loading and 5%~12% under frontal loading with increased passive viscoelasticity, whereas greater muscle strength reduced axonal strain without a corresponding reduction in pressure. The effects of the two cervical factors also depended on one another: under inertial loading, the mean axonal-strain reduction from increasing strength increased from 21% at D25 to 28% at D95, while the corresponding passive-viscoelasticity effect increased from 32% at S25 to 38% at S95. These findings show that cervical mechanical properties can substantially alter regional brain and axonal response, with passive cervical viscoelasticity producing larger effects than muscle strength across the ranges evaluated.