An investigation into axial impacts of the cervical spine using digital image correlation

Background Context: High-energy impacts are commonly encountered during sports such as Rugby Union. Whilst catastrophic injuries resulting from such impacts are rare, the consequences can be devastating for all those involved. A greater level of understanding of cervical spine injury mechanisms is required, with the ultimate aim of minimizing such injuries.
Purpose: The present study aimed to provide a greater understanding of cervical spine injury mechanisms, by subjecting porcine spinal specimens to impact conditions based on those measured in vivo. The impacts were investigated using high-speed digital image correlation (DIC), a method not previously adopted for spinal impact research.
Study Design: In-vitro biomechanical study
Methods: The study was funded through an institutional grant from the Rugby Football Union Injured Players Foundation. Eight porcine specimens were impacted using a custom-made rig. The cranial and caudal axial loads were measured at 1 MHz. Video data were captured with two cameras at 4 kHz, providing measurements of the 3D deformation and surface strain field of the specimens using DIC.
Results: The injuries induced on the specimens were similar to those observed clinically. The mean (±SD) peak caudal load was 6.0 (±2.1) kN, which occurred 5.6 (±1.1) ms after impact. Damage observable with the video data occurred in six specimens, 5.4 (±1.1) ms after impact, and the peak surface strain at fracture initiation was 4.6 (±0.5) %.
Conclusions: This study has provided an unprecedented insight into the injury mechanisms of the cervical spine during impact loading. The posture represents a key factor in injury initiation, with lordosis of the spine increasing the likelihood of injury.