Estimating the difference in concussion risk reduction between youth hockey helmets

Introduction: Hockey reports the second-highest concussion incidence rate among youth sports, with one study reporting 1.20 concussions per 1000 athletic exposures. Most hockey helmets are designed to meet adult certification requirements which do not represent youth impact conditions. Youth hockey players are more susceptible to concussions than adults due to their brains still developing, increased head-body proportion, and weaker neck musculature that limits their ability to reduce resultant head accelerations due to collisions or falls. Previous work has evaluated the differences in design between youth and varsity hockey helmets but has not compared the performance changes between the two. Overall, this study’s objective was to evaluate youth hockey helmet performance by measuring linear and rotational head accelerations at youth-specific impact conditions and evaluate how helmet characteristics, such as shell construction and liner thickness, impacted performance.

Materials and

Methods: Twenty-four helmets were chosen to represent available brands and helmets on the market. Each helmet was tested at three pendulum impact speeds (2.3, 3.4, 4.9 m/s) and four impact locations (front, back, side, rearboss) (Figure 1). A rigid impacting face was chosen to simulate the rigid surfaces in hockey and to eliminate any differences between helmets in comparative testing due to impactor compliance. The pendulum impacted a helmeted small NOCSAE headform weighing 4.9 kg, which is modified to fit a 5th percentile female Hybrid III neck. This configuration has been shown to represent a 10- to 12-year-old boy. The head and neck were mounted to a 5-degree-of-freedom slide table with an 8 kg sliding mass. The NOCSAE headform was instrumented with three linear accelerometers and a triaxial angular rate sensor (ARS) at its center of gravity to measure linear and rotational impact kinematics. Once testing was completed, a youth-specific risk function was used to estimate concussion risk and rank helmets by combining peak linear acceleration (PLA) and peak rotational acceleration (PRA) across each of the four locations and three speeds tested. Characterization of youth helmet decoupling technologies and liner thickness was completed. Helmets were characterized as having one-piece or multiple-piece shell constructions. Helmet liner thickness was measured at each impact location. A linear mixed model was used with helmet model as a random effect to quantify the effects of location, speed, shell construction, and liner thickness on PLA, PRA, and concussion risk.

Results, Conclusions, and Discussions: After comparing medium and high-energy impacts, we found there were large differences in concussion risk differences between helmets. Helmet performance varied, with the Warrior Covert RS PRO being the best overall performer as it yielded a 7.5% medium impact concussion risk value (Confidence Interval (CI 5.4%-9.5%)) and 49.8% high impact concussion risk value (CI 43.0%-56.7%). The Warrior Alpha One Pro was the worst performer as it yielded a 32.4% medium impact concussion risk value (CI 24.3%-40.4%) and 83.2% high impact concussion risk value (CI 76.9%-89.4%). Impact speed and impact location affected PLA, PRA, and concussion risk (p < 0.001). Neither shell construction (p = 0.876) nor liner thickness (p = 0.194) influenced the PLA. We also saw no effect of liner thickness on PRA (p = 0.142). However, two-piece shells were associated with an average reduction in PRA by 776 rad/s^2 (p = .004). Correspondingly, concussion risk was not affected by liner thickness (p = 0.811) but was affected by shell construction (p = 0.005), as helmets with two shell pieces reduced concussion risk by 7.7%. The reduction in PRA and concussion risk found with helmets that included two shell pieces is thought to be due to the decoupling occurring between the shell pieces during an impact. Most youth helmets were simply smaller versions of varsity helmets. Instead of decreasing a varsity helmet's size and liner thickness, companies should integrate padding specific to the head impacts youth players experience. The development of a youth-specific hockey helmet test standard would be a good first-step to encourage hockey helmet manufacturers to develop youth-specific helmets.

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