Traumatic instabilities of the cervical spine caused by high-speed axial compression in a human model - An in vitro biomechanical study

Study Design. Traumatic injury of the cervical spine was produced on human cadavers and evaluated with instability tests and radiographs. Objective. To relate traumatic injuries of the cervical spine to instabilit y and patterns of traumatic injury to different levels of impact energy. Summary of Background Data. Data from young human cadavers are rare in trau matic models of the cervical spine, and instabilities caused by axial compr ession with different impacts remain unknown. Methods. Fourteen cervical spine specimens (C2-C4) obtained from fresh huma n cadavers were divided evenly into two groups and subjected to axial compr essive impact with 30 J and 50 J impact energy, respectively. Pure moments in flexion-extension, left/right lateral bending, and left/right axial rota tion were applied to each specimen before and after trauma. The maximum mom ent was 2.0 Nm in each case. Ranges of motion and neutral zones were measur ed using stereophotogrammetry. Results. Ranges of motion and neutral zones for both groups increased after trauma. No bony injury was observed on the radiographs after trauma with 3 0 J, but motions increased significantly in flexion, extension, and axial r otation. All specimens showed bony injuries after trauma with 50 J, whereas motions continued to increase significantly in all directions. The relativ e neutral zone values were larger than the corresponding range of motion va lues, except in flexion-extension after trauma with 50 J. Conclusions. The injury patterns of the cervical spine were associated with impact energy, and a high level of impact energy could produce either thre e-column injury or anterior middle-column injury. Instabilities of the cerv ical spine caused by compressive trauma increased with the level of impact energy. The neutral zone was more sensitive than the range of motion in rep resenting spinal instability, whereas instability testing was more sensitiv e than radiographs in evaluating traumatic injury of cervical spine.