Forces during head-to-chest impact in American football
Much of the existing concussion research focuses on the direct impact to the head, but it is also known that forces that go through the body following a chest impact can result in a concussion.
This study aimed to determine the forces going through the chest during a head-to-chest collision in American football. Forces were measured both with and without a helmet.
On top of that, a finite element study was conducted using a Global Human Body Model Consortium (GHBMC) to investigate the forces through the cervical spine upon impact.
In a simulated model, the following forces and motions were registered: upper neck tensile forces, and strain. The tensile forces were recorded as neural strain vs. cervical spine rotation. Average strains were 0.21% strain/ degree of cervical spine rotation and 4.6% strain/ 1000N of tensile load. The maximum strain in the vertebral column was predicted to occur in the upper cervical spine (C1–C2).
The findings of head-to-chest impacts both with and without a helmet were used to estimate strain along the spinal cord and brainstem. The estimated strain was 13.0%–18.6% in helmet to chest contact and 8.7%–12.2% in case of no helmet to chest contact due to combined tension and forward flexion. This range represents the estimated average strain (low) to the maximum strain (high). Remarkably, even the lowest ends of this strain exceeded the level known to have a functional change on the neural tissue.
The authors of this study also reference a study by Breig, in which it was found that under tension and flexion forces through the upper cervical spine, the medulla oblongata (which helps regulate breathing and heart rate function) was stretched most. This is interesting, and consistent with those who have been concussed by impact resulting in cervical tension and flexion.
The results of this study highlight that the added weight and force behind a helmet can impact overall forces through the cervical spine.
This is information which can be helpful for helmet manufacturers, but from a clinical perspective also for understanding the forces going through the cervical spine: even when the head and neck are not directly contacted, these forces can still have a very significant impact on the cervical spine.
Expert opinion by Jessica Povall
Very little research exists involving the forces going through the cervical spine, and especially evaluating the neural tissue tensile forces during an impact such as in American football.
This article highlights that the neural stretch and impact on the brain stem and spinal cord should be taken into serious consideration. Often in concussion, the focus is on the cervical vertebrae and the brain itself, but forces through the lower brainstem and how these can play a role in concussion are also important to consider.
Accentuating the potential for tissue stretch in the medulla oblongata during this type of injury allows health care professionals to be aware of the impacts on consciousness during this type of injury, as well as the overall need to consider the brainstem and safety of the cervical spine during impacts such as these.
> From: Jadischke et al., BMJ Open Sport Exerc Med 4 (2018) e000362. All rights reserved to The Author(s). Click here for the online summary.