The Biomechanics of Concussion in Unhelmeted Australian Football Players

Background: Concussion is a prevalent brain injury in sport and the wider community. Despite this, little research has been conducted investigating the dynamics of impacts to the unprotected human head and injury causation in vivo, in particular the roles of linear and angular head acceleration. Methods: The dynamics of no-injury head impact cases from elite Australian football were estimated using quantitative video measurement methods and rigid body simulations using pedestrian human facet models. The 13 no-injury head impact cases were collated with 27 previously analysed concussion cases. Logistic regression analyses were conducted to investigate associations between head impact kinematics and concussion. Results: Qualitative analysis showed that the head was vulnerable to lateral impacts. Logistic regression analyses of head acceleration and velocity components revealed that angular acceleration of the head in the coronal plane had the strongest association with concussion. Tentative tolerance levels of 1747 rad·s-2 and 2296 rad·s-2 47 were reported for a 50% and 75% likelihood of concussion, respectively. Conclusion: As hypothesised by Holbourn over 70 years ago, angular acceleration plays an important role in the pathomechanics of concussion, which has major ramifications in terms of helmet design and other efforts to prevent and manage concussion