Annals of Biomedical Engineering, Vol. 46, No. 7, July 2018 (Ó 2018) pp. 986–1000 https://doi.org/10.1007/s10439-018-2017-7 Comparison of Ice Hockey Goaltender Helmets for Concussion Type Impacts 1,2 2 2,3 2 J. MICHIO CLARK, KAREN TAYLOR, ANDREW POST, T. BLAINE HOSHIZAKI, 1,2 and MICHAEL D. GILCHRIST 1School of Mechanical & Materials Engineering, University College Dublin, Belfield, Dublin 4, Ireland; 2School of Human Kinetics, University of Ottawa, 200 Lees Ave., Room A106, Ottawa, ON K1N 6N5, Canada; and 3Division of Neurosurgery, St. Michael’s Hospital, 30 Bond St, Toronto, ON M5B 1W8, Canada (Received 29 November 2017; accepted 24 March 2018; published online 29 March 2018) Associate Editor Joel D. Stitzel oversaw the review of this article. Abstract—Concussions are among the most common injuries INTRODUCTION sustained by ice hockey goaltenders and can result from collisions, falls and puck impacts. However, ice hockey Goaltender masks were introduced into ice hockey goaltender helmet certification standards solely involve drop to reduce the risk of facial fracture.17 As technology tests to a rigid surface. This study examined how the design advanced, the goaltender mask evolved into a helmet/ characteristics of different ice hockey goaltender helmets affect head kinematics and brain strain for the three most cage combination, rather than a single piece full common impact events associated with concussion for fiberglass mask. Today, ice hockey goaltender helmets goaltenders. A NOCSAE headform was impacted under are typically made with a cage of carbon, steel, or conditions representing falls, puck impacts and shoulder titanium, a helmet shell of carbon and Kevlar com- collisions while wearing three different types of ice hockey posite, fiberglass, or polycarbonate and an energy ab- goaltender helmet models. Resulting linear and rotational acceleration as well as maximum principal strain were sorbing liner consisting of vinyl nitrile (VN) foam. Ice measured for each impact condition. The results indicate hockey goaltender helmet designs have progressed to that a thick liner and stiff shell material are desirable design the point where traumatic brain injuries (TBI) have characteristics for falls and puck impacts to reduce head become infrequent in the sport of ice hockey, however kinematic and brain tissue responses. However for collisions, concussions remain a common injury.21,30,63 In the the shoulder being more compliant than the materials of the helmet causes insufficient compression of the helmet mate- National Collegiate Athletic Association (NCAA) rials and minimizing any potential performance differences. concussions have been reported to be the second most This suggests that current ice hockey goaltender helmets can common injury sustained by ice hockey goaltenders be optimized for protection against falls and puck impacts. with an incidence of 1.7 per year.30 The performance of However, given collisions are the leading cause of concussion ice hockey goaltender helmets has been evaluated using for ice hockey goaltenders and the tested helmets provided little to no protection, a clear opportunity exists to design certification standards that primarily involve drop tests new goaltender helmets which can better protect ice hockey using measures of peak linear acceleration to establish goaltenders from collisions. impact attenuation properties.1,6,7,22 This has resulted in ice hockey goaltender helmets using materials which Keywords—Brain injury, Ice hockey, Helmet, Impact biome- are designed to protect against falls. In addition to chanics, Finite element modeling. falls, ice hockey goaltenders can face pucks exceeding 100 mph (161 km/h) and collisions with players trav- eling at speeds up to 30 mph (48 km/h), which pose a high risk of injury.60 As a result, it is important that ice hockey goaltender helmets use materials that are not only designed to protect against falls but also against puck impacts and collisions. Ice hockey goaltenders can suffer concussions from Address correspondence to J. Michio Clark, School of Mechan- falls, puck impacts and collisions, of which collisions ical & Materials Engineering, University College Dublin, Belfield, 30 Dublin 4, Ireland. Electronic mail: [email protected] are the leading cause of concussion. Falls, puck im- 986 0090-6964/18/0700-0986/0 Ó 2018 Biomedical Engineering Society Comparison of Ice Hockey Goaltender Helmets 987 pacts, and collisions in ice hockey create unique load- the inbound impactor (Fig. 1b). The error associated ing conditions which are applied to the head and with this method was estimated between 5 and 18% for brain.18,23–25,37,38,53,58 Differences in impact loading velocity and 10° for impact orientation.44,53 The error conditions have been shown to affect the protective was determined by measuring skating velocity capabilities of helmets.2,5,10 It is important to gain an obtained from Kinovea compared to high speed understanding of how different materials used in hel- video.44 The velocities selected for the event specific mets perform under multiple events associated with impact protocol were taken from the cases which were concussion in order to improve helmet design. Ice determined to have the lowest and highest velocity for hockey goaltender helmets have been compared for each impact event. The mean velocity for each impact their protection from puck impacts as measured by event was also selected. These velocities were selected head kinematics,37 however it is currently unknown for the event specific impact protocol to represent the how different designs and materials used ice hockey energy levels associated with each impact event. These goaltender helmets affect head kinematics and brain velocities are presented in Table 1.3 Impact locations response for other impact events associated with con- for each case was determined according to the refer- cussion. Research in ice hockey helmets has shown that ence presented in Fig. 2.2,53 The locations selected for design characteristics such as external shell geometry, the impact protocol were those which represented the shell and liner material, and liner thickness can influ- best coverage of possible impact for each event and are ence kinematic and brain tissue response.19,38,43,56,59 shown in Fig. 3.3 Similar research for goaltender helmets is lacking, and Nine helmets of each model were impacted under if performed would provide useful information for the test conditions; a new helmet was used for each future design considerations to improve protection. As impact event and velocity. Overall, 243 impacts were a result, the purpose of this study was to examine how conducted, in which three trials were performed for liner thickness and shell material of ice hockey goal- each impact condition. The peak linear and rotational tender helmets would affect the head kinematics and acceleration of the headform were obtained for each brain strain for the three most common impact events impact. The linear and rotational acceleration curves associated with concussion in ice hockey. were transformed using a rotation matrix prior to in- putting the kinematic response into a finite element brain trauma model. Within the NOCSAE headform, MATERIALS AND METHODS the accelerometer blocks are orientated at 25° with respect to the y-axis about the centre of gravity. To Procedure align the kinematic response of the NOCSAE head- The ice hockey goaltender helmets were impacted form with the coordinate system used by the finite under conditions representing falls, puck impacts and brain trauma model the following rotational matrix collisions. The impact protocol used in this study was curve was applied to the linear and rotational accel- based on video analysis of 12 real world ice hockey eration curves at the centre of gravity of the headform: 2,3 2 3 goaltender concussions. The videos used for this cosðhÞ 0 sinðhÞ protocol were those in which the event was of sufficient 4 5 RyðÞ¼h 010 ð1Þ quality to identify impact parameters and the goal- À sinðhÞ 0 cosðhÞ tender was diagnosed with a concussion by a medical doctor. These concussive events were the result of a where, h is the angle between the frame of reference fall, puck, or collision. Video analysis was performed used by the NOCSAE headform and the finite element using Kinovea 0.8.2 video analysis software (Ki- brain trauma model. The rotation matrix described in novea.org), as described by Post et al.,43 Rousseau53 Eq. (1) when applied to acceleration-time histories and Clark et al.3 to determine impact parameters such from an accelerometer block orientated at 25° resulted as velocity, orientation and location. A perspective in mean linear and rotational acceleration-time histo- grid based on known points and distances on the ice ries which were within the 95% confidence interval of was applied to determine impact velocities and orien- acceleration-time histories from a 0° accelerometer tations for each concussive case. The perspective grid block orientation with minor periods in which the allowed for the measurement of distances and angles acceleration-time histories differed.4 The differences on the playing surface. Velocity was determined by were within ± 7 g and ± 700 rad/s2 and as a result measuring the distance between the struck player’s rotated linear and rotational curves were considered to head and the impacting surface five frames prior to be similar. As the rotated linear and rotational curves impact (Fig. 1a). Impact orientation was measured by were similar, the curves could be input into a finite the angle between the struck player’s head position and element brain trauma model for use in head impact 988 CLARK et al. FIGURE 1. Examples of a perspective grid calibration used in ice hockey to determine: (a) velocity and (b) orientation. TABLE 1. Impact velocities used in event specific impact test protocol for ice hockey goaltender helmets determined from video analysis of real world ice hockey goaltender concussion.3 Velocities (m/s) Impact event Lower Mean Upper Fall 3.5 4.2 5.0 Puck 29.3 35.8 42.3 Collisions 5.2 7.3 9.1 biomechanics research.4 The rotated kinematic radius 68.0 mm and height 21.5 mm.