K15 - The potential effects of youth hockey helmet shell add-ons

Introduction: : Hockey reports the second-highest concussion incidence rate among youth sports, with an estimated rate of 1.20 concussions per 1000 athletic exposures occurring in the sport. Most hockey helmets are designed to meet adult certification requirements that do not represent youth impact conditions. Youth hockey players are more susceptible to concussions than adults because their brains are still developing, their head-body proportion is increased, and their neck musculature is weaker, limiting their ability to reduce head accelerations resulting from collisions or falls. Inspired by helmet shell add-ons that are being adopted in football to lower concussion risk, this study’s objective was to evaluate whether adding padding to the outside of a youth hockey helmet improves overall performance by reducing linear and rotational head accelerations under youth-specific impact conditions.

Materials and

Methods: : Six helmets were selected to represent varying levels of performance (high, medium, low) of youth hockey helmets based on a previously developed youth hockey helmet testing protocol. Each helmet was tested at four locations (front, back, side, rear boss), three speeds (2.3, 3.4, 4.9 m/s), and four shell add-ons (control, one-inch VN600 pad, one-inch D3O pad, Guardian Cap) (Figure 1). A rigid impacting face was chosen to simulate hard surfaces in hockey and to isolate helmet performance. The pendulum impacted a small NOCSAE helmeted headform weighing 4.9 kg with a 5th percentile female Hybrid III neck mounted to an 8 kg sliding torso mass. The NOCSAE headform was instrumented with three linear accelerometers and a triaxial angular rate sensor (ARS) at its center of gravity. Data were sampled at 20 kHz and filtered using a 4-pole Butterworth low-pass filter with a cutoff frequency of 1650 Hz for accelerometers and 300 Hz for the ARS. Once testing was completed, a youth-specific risk function was used to estimate concussion risk from peak linear acceleration (PLA) and peak rotational acceleration (PRA). We used R (Version 3.3.0, RStudio; Boston, Massachusetts, USA) to evaluate PLA, PRA, and concussion risk using linear mixed-effect regression (LMER) (lmerTest Package), with a significance level α < 0.05. Separate LMER models for each dependent variable compared location, speed, and helmet shell add-on, including helmet type as a random effect.

Results, Conclusions, and Discussions:: Impact speed, impact location, and externally mounted padding affected PLA, PRA, and concussion risk (all p< 0.001). Each add-on configuration was compared to the control helmet. VN600 padding yielded a 33.2 g reduction in PLA (Confidence interval [CI] 26.0-40.3 g, p< 0.001) and a 1657 rad/sec² reduction in PRA (CI 1048-2266 rad/sec², p< 0.001), which combined to reduce overall concussion risk by 23.7% (CI 16.9%-30.4%, p< 0.001). D3O padding yielded a 31.0 g reduction in PLA (CI 24.0-38.0 g, p< 0.001) and a 1569 rad/sec² reduction in PRA (975-2162 rad/sec², p< 0.001), leading to an overall 22.7% reduction of concussion risk (16.1%-29.3%, p< 0.001). The guardian cap yielded an 11.1 g reduction in PLA (4.3-18.0 g, p=0.004) and a 612 rad/sec² reduction in PRA (CI 33.5-1190 rad/sec², p=0.050), which reduced overall concussion risk by 7.0% (CI 0.5-13.4%, p=0.047).
Adding external padding improves helmet performance, as VN600 padding and D3O padding reduced concussion risk compared to the control helmet (p < 0.001). The Guardian Caps also reduced concussion risk (p < 0.047), but not to the extent of the D3O and VN600 foams. This is due to the thickness of the VN600 and D3O foams, which were one inch thick, while the Guardian Cap pad was only half an inch thick. Most youth hockey helmets are smaller versions of varsity hockey helmets and are not optimized for youth impact-specific speeds. The substantial improvement in performance associated with the add-ons suggests there is further room to optimize youth hockey helmet design. Thus, when designing youth hockey helmets and external padding technologies, manufacturers should focus on both the thickness and composition of foam materials to account for a range of impact scenarios.

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