The biomechanics of concussion in unhelmeted football players in Australia: a case-control study

Abstract

Objective: 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.

Setting: Professional contact football in Australia.

Participants: Adult male professional Australian rules football players participating in 30 games randomly selected from 103 games. Cases selected based on an observable head impact, no observable symptoms (eg, loss-of-consciousness and convulsions), no on-field medical management and no injury recorded at the time.

Primary and secondary outcome measures: A data set for no-injury head impact cases comprising head impact locations and head impact dynamic parameters estimated through rigid body simulations using the MAthematical DYnamic MOdels (MADYMO) human facet model. This data set was compared to previously reported concussion case data.

Results: Qualitative analysis showed that the head was more 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) were reported for a 50% and 75% likelihood of concussion, respectively. The mean maximum resultant angular accelerations for the concussion and no-injury cases were 7951 rad/s(2) (SD 3562 rad/s(2)) and 4300 rad/s(2) (SD 3657 rad/s(2)), respectively. Linear acceleration is currently used in the assessment of helmets and padded headgear. The 50% and 75% likelihood of concussion values for resultant linear head acceleration in this study were 65.1 and 88.5 g, respectively.

Conclusions: 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.

Keywords: Public Health; Sports Medicine.

Figure 1

Flow chart of concussion and no-injury case selection. The rigid body reconstruction concussion cases comprised 23 Australian football and 4 rugby league cases. Australian football is also referred to in the text as Australian rules football.

Figure 2

Mean peak linear acceleration of the head, for all unique directional components (X, −X, Y, Z, −Z) and resultant (R). Significance levels: *p<0.01, **p<0.001 (two-sample t test for unequal variance). Error bars represent one SD.

Figure 3

Mean peak angular acceleration of the head, for all unique directional components (X, Y, −Y, Z) and resultant (R). Significance levels: *p<0.01, **p<0.001 (two-sample t test for unequal variance). Error bars represent one SD.

Figure 4

Mean peak angular velocity of the head, for all unique directional components (X, Y, −Y, Z) and resultant (R). Significance levels: *p<0.01, **p<0.001 (two-sample t test for unequal variance). Error bars represent one SD.