Aims
Subaxial cervical facet dislocation (CFD), a serious consequence of head-first impacts (HFI), often results in tetraplegia1. The mechanisms underlying CFD remain unclear, and replication in computational and experimental settings has proven challenging. Prior studies suggest that a non-neutral head-forward posture with a horizontal Frankfort plane (FP) may elevate CFD risk2. This study tested that hypothesis using parametric finite element (FE) simulations and cadaveric validation experiments.
Methods
Eleven HFI simulations were performed using a detailed FE model of the human head and neck, replicating previous inverted drop cadaver experiments. The model was repositioned to represent head-forward eccentricity conditions (0, 5, ..., 50 mm; horizontal FP), then subjected to vertical impact at 2 m/s. Kinematic and kinetic data were recorded at 100 kHz.
Four human cadaveric head–neck specimens underwent matched inverted drop tests at 2 m/s using 30 mm head eccentricity. Impact forces (50 kHz) and cervical kinematics (10 kHz) were recorded, and post-impact injuries were documented.
Results
Simulations reproduced the characteristic “S-shaped” cervical deformation observed in prior studies. Increasing head eccentricity led to progressively higher anterior shear forces at the lower cervical spine, with eccentricities above 15 mm exceeding physiological thresholds. Although limitations in soft-tissue failure modelling prevented CFD in simulations, 3 of 4 cadaver tests resulted in complete C7/T1 facet dislocation.
Conclusion
Pre-impact head-forward posture increases the risk of lower cervical dislocation by amplifying intervertebral shear forces during HFI. These findings support the importance of neutral head alignment in at-risk scenarios and demonstrate the value of integrating computational and experimental models to better understand and prevent spinal injury.