Background Concussion is a prominent injury risk in sport, but the mechanisms that cause concussion are unclear. An important debate centres on the roles of angular and linear head acceleration in the mechanism of concussion. Resolving this debate is a prerequisite for developing injury prevention methods.

Objective To estimate the brain loading patterns in a case series of concussive and no-injury head impacts. To assess the relative affects of linear and angular acceleration on brain loading and injury.

Design Biomechanical analysis of head impacts using the validated KTH human head finite element model to analyse brain loading patterns in reconstructed head impacts.

Setting Professional male unhelmeted contact football.

Participants Biomechanical data from a previous case series study of 40 male football players (concussed and no-injury).

Main outcome measurements Maximum principle strain, a predictor of injury, was measured in discrete brain locations.

Results The highest maximum principle strains were recorded in both the white and grey matter of the cerebrum. Strains in all brain regions were similar across all three grades of concussion (Cantu Revised Concussion Grading Guidelines), but lower (33–47%) for no-injury cases. Concussion was most correlated with strains in the brainstem and thalamus. Angular, rather than linear, resultant accelerations correlated higher to strains in all regions of the brain. Angular accelerations in the coronal plane and linear accelerations directed inferiorly had the greatest correlation to concussion and loss of consciousness. For linear accelerations, those directed laterally and inferiorly were most correlated with strain. Angular accelerations in the coronal plane correlated highly with strains in the brainstem, thalamus, and midbrain. Angular accelerations in the transverse plane correlated highly with strains in the cerebrum and corpus callosum.

Conclusion Brain loading differences were observed between concussion and no-injury cases. Angular acceleration may play a more important role in the mechanism of concussion than linear acceleration.