The Influence of Neck Stiffness, Impact Location, and Angle on Peak Linear Acceleration, Shear Force, and Energy Loading Measures of Hockey Helmet Impacts

Abstract

Head and brain injuries like concussion affect many hockey players throughout their playing careers. Hockey helmets remain to be the best form of head protection available as they function well to reduce the occurrence of skull fracture by minimizing linear accelerations and force transfer to the head. Currently, among helmet testing protocols and the literature, there is a large focus on peak linear acceleration reduction and the comparison of injury risk across impact conditions relative to linear accelerations felt by the brain. Additionally, gaps exist analyzing how certain impact characteristics like impact angle and neck stiffness influence injury risk. The purpose of this study was to examine the influence that impact angle, neck stiffness, and impact location have on commonly analyzed variables such as peak linear acceleration and Severity Index, while also analyzing differences in shear force and energy loaded onto the head and neck. The study served to create a model to compute the amount of energy loaded into the system composed of head, neck and helmet and to determine the strength of the relationship between the amounts of energy loaded into the system and the risk of injury estimated by Severity Index values. The study involved an analysis of 18 impacts at different velocities per helmet impact locations using a combination of three neck stiffness and two impact angles. In total, 540 impacts were conducted and analyzed. The findings were analyzed and an interaction effect with a medium effect size was observed between impact angle and impact location when measuring peak linear acceleration, F(8, 510)= 16.174, p< .005, η2= .113. Also, interaction effects with small effect sizes were determined between impact angle and impact location, F(4, 510)= 11.977, p< .005, η2= .086, as well as between neck torque and impact angle when measuring the amount of energy loaded onto the system, F(2, 510)=3.700, p= .025, η2= .014. An interaction effect with a medium effect size was also observed between impact angle and impact location when measuring Severity Index, F(4, 510)= 12.795, p<0.005, η2= .091. Finally, a three-way interaction with a small effect size was observed between the variables when measuring shear force applied to the headform, F(8, 510)= 5.550, p< .005, η2= .080. A model to predict energy loaded was also created using impact location, angle of impact, peak linear acceleration, and peak shear force as predictors, F(5, 535)= 54.190, p< .005. In addition to these findings, a moderate correlation between Severity Index and the amount of energy loaded onto the system was determined, r= .340, p< .05. This study served to build on previous research analyzing helmeted impacts in an attempt to improve understanding of injury mechanisms.