A Parametric Analysis of Embedded Tissue Marker Properties and Their Effect on the Accuracy of Displacement Measurements.

Datasets obtained from cadaveric experimentation are broadly used in validating finite element models of head injury. Due to the complexity of such measurements in soft tissues, experimentalists have relied on tissue-embedded radiographic or sonomicrometry tracking markers to resolve tissue motion caused by impulsive loads. Dynamic coupling of markers with the surrounding tissue has been a previous concern, yet a thorough sensitivity investigation of marker influences on tissue deformation has not been broadly discussed. Technological improvements to measurement precision have bolstered confidence in acquired data; however, precision is often conflated with accuracy; the inclusion of markers in the tissue may alter its natural response, resulting in a loss of accuracy associated with an altered displacement field. To gain an understanding of how marker properties may influence the measured response to impact, we prepared a set of nine marker designs using a Taguchi L9 array to investigate marker design choice sensitivity. Each of these designs was cast into a block of tissue simulant and subjected to repeated drop tests. Vertical displacement was measured and compared to the response of the neat material, which contained massless tracking markers. Medium density and medium stiffness markers yielded the least deviation from the neat material response. The results provide some design guidelines indicating the importance of maintaining marker matrix density ratio below 1.75 and marker stiffness below 1.0 MPa. These properties may minimize marker interference in tissue deformation. Overall, embedded marker properties must be considered when measuring the dynamic response of tissue.

The Influence of Neck Stiffness on Head Kinematics and Maximum Principal Strain Associated With Youth American Football Collisions.

Understanding the relationship between head mass and neck stiffness during direct head impacts is especially concerning in youth sports where athletes have higher proportional head mass to neck strength. This study compared 2 neck stiffness conditions for peak linear and rotational acceleration and brain tissue deformations across 3 impact velocities, 3 impact locations, and 2 striking masses. A pendulum fitted with a nylon cap was used to impact a fifth percentile hybrid III headform equipped with 9 accelerometers and fitted with a youth American football helmet. The 2 neck stiffness conditions consisted of a neckform with and without resistance in 3 planes, representing the upper trapezius, the splenius capitis, and the sternocleidomastoid muscles. Increased neck stiffness resulted in significant changes in head kinematics and maximum principal strain specific to impact velocity, impact location, and striking mass.

Biomechanical Comparison of Real World Concussive Impacts in Children, Adolescents, and Adults.

Accidental falls occur to people of all ages, with some resulting in concussive injury. At present, it is unknown whether children and adolescents are at a comparable risk of sustaining a concussion compared to adults. This study reconstructed the impact kinematics of concussive falls for children, adolescents, and adults and simulated the associated brain tissue deformations. Patients included in this study were diagnosed with a concussion as defined by the Zurich Consensus guidelines. Eleven child, 10 adolescent, and 11 adult falls were simulated using mathematical dynamic models(MADYMO), with three ellipsoid pedestrian models sized to each age group. Laboratory impact reconstruction was conducted using Hybrid III head forms, with finite element model simulations of the brain tissue response using recorded impact kinematics from the reconstructions. The results of the child group showed lower responses than the adolescent group for impact variables of impact velocity, peak linear acceleration, and peak rotational acceleration but no statistical differences existed for any other groups. Finite element model simulations showed the child group to have lower strain values than both the adolescent and adult groups. There were no statistical differences between the adolescent and adult groups for any variables examined in this study. With the cases included in this study, young children sustained concussive injuries at lower modeled brain strains than adolescents and adults, supporting the theory that children may be more susceptible to concussive impacts than adolescents or adults.

Distribution of Brain Strain in the Cerebrum for Ice Hockey Goaltender Impacts.

Concussions are among the most common injuries sustained by goaltenders. Concussive injuries are characterized by impairment to neurological function which can affect many different brain regions. Understanding how different impact loading conditions (event type and impact site) affect the brain tissue response may help identify what kind of impacts create a high risk of injury to specific brain regions. The purpose of this study was to examine the influence of different impact conditions on the distribution of brain strain for ice hockey goaltender impacts. An instrumented headform was fitted with an ice hockey goaltender mask and impacted under a protocol which was developed using video analysis of real world ice hockey goaltender concussions for three different impact events (collision, puck, and fall). The resulting kinematic response served as input into the University College Dublin Brain Trauma Model, which calculated maximum principal strain in the cerebrum. Strain subsets were then determined and analyzed. Resulting peak strains (0.124 - 0.328) were found to be within the range for concussion reported in the literature. The results demonstrated that falls and collisions produced larger strain subsets in the cerebrum than puck impacts which is likely a reflection of longer impact duration for falls and collisions than puck impacts. For each impact event, impact site was also found to produce strain subsets of varying size and configuration. The results of this study suggest that the location and number of brain regions which can be damaged depend on the loading conditions of the impact.

Ice Hockey Summit II: zero tolerance for head hits and fighting.

OBJECTIVE: To present currently known basic science and on-ice influences of sport-related concussion (SRC) in hockey, building on the Ice Hockey Summit I action plan (2011) to reduce SRC. METHODS: The prior summit proceedings included an action plan intended to reduce SRC. As such, the proceedings from Summit I served as a point of departure, for the science and discussion held during Summit II (Mayo Clinic, Rochester MN, October 2013). Summit II focused on (1) Basic Science of Concussions in Ice Hockey: Taking Science Forward; (2) Acute and Chronic Concussion Care: Making a Difference; (3) Preventing Concussions via Behavior, Rules, Education and Measuring Effectiveness; (4) Updates in Equipment: their Relationship to Industry Standards; and (5) Policies and Plans at State, National and Federal Levels to reduce SRC. Action strategies derived from the presentations and discussion described in these sectors were subsequently voted on for purposes of prioritization. The following proceedings include knowledge and research shared by invited faculty, many of whom are health care providers and clinical investigators. RESULTS: The Summit II evidence-based action plan emphasizes the rapidly evolving scientific content of hockey SRC. It includes the most highly prioritized strategies voted on for implementation to decrease concussion. CONCLUSIONS: The highest priority action items identified from the Summit includes the following: (1) eliminate head hits from all levels of ice hockey, (2) change body-checking policies, and (3) eliminate fighting in all amateur and professional hockey.

Ice Hockey Summit II: zero tolerance for head hits and fighting.

This study aimed to present currently known basic science and on-ice influences of sport-related concussion (SRC) in hockey, building upon the Ice Hockey Summit I action plan (2011) to reduce SRC. The prior summit proceedings included an action plan intended to reduce SRC. As such, the proceedings from Summit I served as a point of departure for the science and discussion held during Summit II (Mayo Clinic, Rochester, MN, October 2013). Summit II focused on (1) Basic Science of Concussions in Ice Hockey: Taking Science Forward, (2) Acute and Chronic Concussion Care: Making a Difference, (3) Preventing Concussions via Behavior, Rules, Education, and Measuring Effectiveness, (4) Updates in Equipment: Their Relationship to Industry Standards, and (5) Policies and Plans at State, National, and Federal Levels To Reduce SRC. Action strategies derived from the presentations and discussion described in these sectors were voted on subsequently for purposes of prioritization. The following proceedings include the knowledge and research shared by invited faculty, many of whom are health care providers and clinical investigators. The Summit II evidence-based action plan emphasizes the rapidly evolving scientific content of hockey SRC. It includes the most highly prioritized strategies voted on for implementation to decrease concussion. The highest-priority action items identified from the Summit include the following: (1) eliminate head hits from all levels of ice hockey, (2) change body checking policies, and (3) eliminate fighting in all amateur and professional hockey.

A comparison of frequency and magnitude of head impacts between Pee Wee And Bantam youth ice hockey.

The purpose of this research was to compare the frequency and magnitude of head impact events between Pee Wee and Bantam ice hockey players. Videos of Pee Wee and Bantam boys' ice hockey were analysed to determine the frequency and type of head impact events. The head impact events were then reconstructed in the laboratory using physical and finite element models to determine the magnitude of strain in the brain tissues. The results showed that Pee Wee boys experienced more head impacts from elbows and boards, while Bantam players had more head impacts to the glass. Pee Wee and Bantam players experienced similar frequency and magnitudes of very low, low, and medium and above (med+) levels of strain to the brain. This research suggests to ice hockey leagues and coaches that to reduce the incidence of these levels of brain trauma, consideration must be given to either reducing the level of contact along the boards or the removal of body checking. In addition, companies who innovate in ice hockey should develop protective devices and equipment strategies that aim to reduce the risk of head injury from shoulder and glass impacts for Bantam players.

A video analysis examination of the frequency and type of head impacts for player positions in youth ice hockey and FE estimation of their impact severity.

This research employed head impact frequency and frequency of estimated strain to analyse the influence of player position on brain trauma in U15 and U18 youth ice hockey. The methods involved a video analysis of 30 U15 and 30 U18 games where frequency, type of head impact event, and player position during impact was recorded. These impacts were then simulated in the laboratory using physical reconstructions and finite element modelling to determine the brain strains for each impact category. U15 forwards experienced significantly higher head impact frequencies (139) when compared to defenceman (50), with goalies showing the lowest frequency (6) (p < 0.05). U18 forwards experienced significantly higher head impact frequencies (220) when compared to defenceman (92), with goalies having the least frequent head impacts (4) (p < 0.05). The U15 forwards had a significantly higher frequency of head impacts at the very low and med strains and the U18s had higher frequency of head impacts for the very low and low level strains (p < 0.05). Game rule changes and equipment innovation may be considered to mitigate the increased risk faced by forwards compared to other positions in U15 and U18 youth ice hockey.

Head trauma analysis of laboratory reconstructed headers using 1966 Slazenger Challenge and 2018 Telstar 18 soccer balls.

Retired soccer players are presenting with early onset neurodegenerative diseases, potentially from heading the ball. It has been proposed that the older composition of soccer balls places higher strains on brain tissues. The purpose of this research was to compare the dynamic head response and brain tissue strain of laboratory reconstructed headers using replicas of the 1966 Slazenger Challenge and 2018 Telstar 18 World Cup soccer balls. Head-to-ball impacts were physically conducted in the laboratory by impacting a Hybrid III head form at three locations and four velocities using dry and wet soccer ball conditions, and computational simulation was used to measure the resulting brain tissue strain. This research showed that few significant differences were found in head dynamic response and maximum principal strain between the dry 1966 and 2018 balls during reconstructed soccer headers. Headers using the wet 1966 soccer ball resulted in higher head form responses at low-velocity headers and lower head responses as velocities increased. This study demonstrates that under dry conditions, soccer ball construction does not have a significant effect on head and brain response during headers reconstructed in the laboratory. Although ball construction didn't show a notable effect, this study revealed that heading the ball, comparable to goalkeeper kicks and punts at 22 m/s, led to maximum principal strains exceeding the 50% likelihood of injury risk threshold. This has implications for the potential risks associated with repetitive heading in soccer for current athletes.

Evaluation of two rotational helmet technologies to decrease peak rotational acceleration in cycling helmets.

The risk of brain trauma has been associated with the rotational kinematics leading to the development of helmets with a variety rotational management technologies. The purpose of this paper was to employ a rotation specific test protocol to evaluate the effectiveness of two of these technologies. Dynamic response of the head was measured to assess the performance of each technology. Three cycling helmets with identical construction were included in this study. One helmet with no rotational technology, an established, commercial technology and a novel helmet rotational technology designed and assembled by the authors were tested. A drop test onto a 45° anvil was used to measure the ability of each helmet to manage the dynamic response of the head form during a series of impacts. The results revealed both rotational helmet technologies resulted in lower peak rotational acceleration and brain strain, however each technology demonstrated unique performance characteristics depending on the impact condition.

Comparison of head impact frequency and magnitude in youth tackle football and ice hockey.

Repetitive head impacts are a growing concern for youth and adolescent contact sport athletes as they have been linked to long term negative brain health outcomes. Of all contact sports, tackle football and ice hockey have been reported to have the highest incidence of head or brain injury however, each sporting environment is unique with distinct rules and regulations regarding contact and collisions. The purpose of this research was to measure and compare the head impact frequency and estimated magnitude of brain tissue strain, amongst youth tackle football and ice hockey players during game play. Head impact frequency was documented by video analysis of youth tackle football and ice hockey game play. Impact magnitude was determined through physical laboratory reconstructions and finite element modelling to estimate brain tissue strains. Tackle football demonstrated significantly higher impact frequency (P < 0.01) and magnitude of estimated brain tissue strains (P < 0.01) compared to ice hockey. A significantly higher number of higher strain head impacts were documented in tackle football when compared to ice hockey (P < 0.01). These differences suggest that youth football players may experience increased frequency and magnitude of estimated brain tissue strains in comparison to youth hockey.

Influence of play type on the magnitude and number of head impacts sustained in youth American football.

The magnitude and number of head impacts experienced by young American football players are associated with negative brain health outcomes and may be affected by play-type strategies. The purpose of this research was to examine how play type affects the magnitude and number of head impacts in youth American tackle football. Head impacts were recorded for 30 games in the 5-9 age category and 30 games in the 9-14 age category. Impacts using physical and finite element models were conducted to determine the brain strain. Run plays had a higher head impact frequency in both age groups (p < 0.05). This increase in head impacts was consistent for all positions (p < 0.05), except wide receiver, and offensive line and defensive back in the 9-14 age group (p > 0.05). Both age groups experienced significantly different magnitude proportions with higher numbers of very low and low strain magnitude impacts during run plays (p < 0.05), and a higher proportion of moderate magnitude impacts in the 5-9 age category (p < 0.05). This data can be used to inform and educate teams and coaches and influence decisions around the use of runs and passing plays that may lead to a decrease in head impacts.

Biomechanical comparison of concussions with and without a loss of consciousness in elite American football: implications for prevention.

Loss of consciousness (LOC) associated with concussion is no longer considered an indicator of severity of injury in concussion management protocols. Studies investigating the association between LOC and recovery time or neurophysiological performance have reported ambiguous findings and resulted in a limited understanding of the severity of LOC-inducing head impacts. Concussive injuries with and without LOC from helmet-to-helmet and shoulder collisions and falls in elite American football were reconstructed in laboratory using a hybrid III headform and finite element model to obtain peak linear and rotational acceleration and brain tissue deformation metrics in the cerebral cortex, the cerebral white matter, the corpus callosum, the thalamus and the brainstem. Impact velocity, peak linear and rotational acceleration were significantly greater in the LOC group than the no LOC group. The brain tissue deformation metrics were greater in the LOC group than the no LOC group. The best overall predictor for LOC was impact velocity. Concussions with LOC are characterised by greater magnitudes of brain tissue deformation. This was mainly the result of higher impact velocities in the LOC group providing league decision-makers with an understanding of the importance of managing impact velocity through athlete education and rule enforcement or change.

The influence of impact surface on head kinematics and brain tissue response during impacts with equestrian helmets.

Current equestrian standards employ a drop test to a rigid steel anvil. However, falls in equestrian sports often result in impacts with soft ground. The purpose of this study was to compare head kinematics and brain tissue response associated with surfaces impacted during equestrian accidents and corresponding helmet certification tests. A helmeted Hybrid III headform was dropped freely onto three different anvils (steel, turf and sand) at three impact locations. Peak linear acceleration, rotational acceleration and impact duration of the headform were measured. Resulting accelerations served as input into a three-dimensional finite element head model, which calculated Maximum principal strain (MPS) and von Mises stress (VMS) in the cerebrum. The results indicated that impacts to a steel anvil produced peak head kinematics and brain tissue responses that were two to three times greater than impacts against both turf and sand. Steel impacts were less than half the duration of turf and sand impacts. The observed response magnitudes obtained in this study suggest that equestrian helmet design should be improved, not only for impacts to rigid surfaces but also to compliant surfaces as response magnitudes for impacts to soft surfaces were still within the reported range for concussion in the literature.

Comparison of frequency and magnitude of head impacts experienced by Peewee boys and girls in games of youth ice hockey.

In youth ice hockey, girls are reported to suffer more concussions than boys, peaking around 13-14 years old, which may be related to differences in the level of brain trauma experienced by the players. The purpose of this research was to describe the differences in brain trauma characteristics, specifically the magnitude and frequency of head impacts between Peewee boys and girls from playing ice hockey. Thirty games of Peewee boys and Peewee girl's ice hockey were recorded to document the head impact events. These events were reconstructed using physical and computational techniques to estimate the strain to the brain tissue. The results found that Peewee boys experienced more head impacts than girls, specifically from the shoulder, ice, boards, and fist/punches (p < 0.05). The boys also experienced more medium strain category impacts (p < 0.05). These results identify that Peewee boys and girls engage in ice hockey differently, which affects the risk of brain trauma likely to be encountered while during game play, suggesting that the increased rate of concussion for girls may not be related to impact magnitudes within the sport but increased reporting of symptoms of concussion or gender differences in brain tissue response to an impact.

Exposure to brain trauma in six age divisions of minor ice hockey.

Acute and chronic neurological risks associated with brain trauma sustained in professional ice hockey has generated concern for youth participants. Minor hockey is a different game when compared to elite players presenting distinctive risk factors for each age division. Objective measures of brain trauma exposure were documented for six divisions in minor ice hockey; U7, U9, U11, U13, U15, U18. Game video analysis, physical reconstruction and computational modelling was employed to capture the event conditions, frequency of impacts, frequency of high strain magnitude (>0.17) impacts, and cumulative trauma. The results showed proportional differences in the event conditions; event type, closing velocity, and head impact location, informing the improvement of age appropriate protection, testing protocols, and safety standards. Frequency of events were highest for U7 when players were learning to skate, and again in U18 as game physicality increases. No significant difference was observed in frequency of high magnitude impacts across age divisions. A peak in high magnitude impacts was empirically observed at both U7 and U15 where skill development in skating and body checking, respectively, were most prominent. Finally, a cumulative trauma metric incorporating frequency and magnitude of impacts provided a detailed analysis of trauma exposure provides for a targeted approach to managing injury risk specific to age division. Objective measures of brain trauma exposure identified in the current study are important to inform strategy, guide legislation and initiate policy for safe play in minor ice hockey.

Intracranial Displacement Measurements Within Targeted Anatomical Regions of a Postmortem Human Surrogate Brain Subjected to Impact.

The dynamic response of the human brain subjected to impulsive loading conditions is of fundamental importance to the understanding of traumatic brain injuries. Due to the complexity of such measurements, the existing experimental datasets available to researchers are sparse. However, these measurements are used extensively in the validation of complex finite element models used in the design of protective equipment and the development of injury mitigation strategies. The primary objective of this study was to develop a comprehensive methodology to measure displacement in specific anatomical regions of the brain. A state-of-the-art high-speed cineradiography system was used to capture brain motion in post-mortem human surrogate specimens at a rate of 7500 fps. This paper describes the methodology used to capture these data and presents measurements from these tests. Two-dimensional displacement fields are presented and analyzed based on anatomical regions of the brain. These data demonstrated a multi-modal displacement response in several regions of the brain. The full response of the brain consisted of an elastic superposition of a series of bulk rotations of the brain about its centre of gravity. The displacement field could be linked directly to specific anatomical regions. The methods presented mark an improvement in temporal and spatial resolution of data collection, which has implications for our developing understanding of brain trauma.

Event-specific impact test protocol for ice hockey goaltender masks.

Goaltenders in the sport of ice hockey are at high risk for concussions from falls to the ice, player collisions and puck impacts. However, current methods used to certify helmets only consider head accelerations for drop tests which may not describe all common injury mechanisms relating to concussion. The purpose of this study was to describe the characteristics of 3 events associated with concussions for ice hockey goaltenders. A helmeted medium National Operating Committee on Standards for Athletic Equipment (NOCSAE) headform was impacted under conditions representing 3 injury events. Three impact locations' velocities were selected for each event based on video analysis of real-world concussive events. Peak resultant linear acceleration, rotational acceleration and rotational velocity of the headform were measured. The University College Dublin Brain Trauma Model (UCDBTM) was used to calculate maximum principal strain (MPS) and von Mises stress in the cerebrum. Each impact event produced a unique dynamic response and brain stress and strain values. This demonstrates that a single impact event (i.e. falls) cannot adequately describe all impact events. As a result, impact protocols which assess multiple impact events such as the protocol described in this study should be used to evaluate ice hockey goaltender masks.

Equestrian Helmet Standards: Do They Represent Real-World Accident Conditions?

The use of helmets in equestrian sports has reduced the occurrence of traumatic brain injuries although, despite improvements to helmets, concussion remains a common injury. Currently, equestrian helmets are designed to pass certification standards involving a linear drop test to a rigid surface, while most concussions in equestrian sports result from oblique impacts to a compliant surface. The purpose of this study was to: (1) Compare the head kinematics and brain tissue response of the current equestrian helmet standard (EN1) and proposed standard EN13087-11 (EN2) to those associated with reconstructions of real-world equestrian concussion accidents. (2) Design a test protocol that would reflect the real-world conditions associated with concussion in equestrian sports. (3) To assess the protective capacity of an equestrian helmet using the flat turf and 45° turf proposed test protocols. Results for reconstructions of real-world concussions were obtained from a previous study (Clark et al. in J. Sci. Med. Sport 23:222-236, 2020). Using one jockey helmet model, impact tests were conducted according to the EN1 and EN2 protocols. Additionally, helmeted and unhelmeted tests were conducted at 5.9 and 6.0 m/s on to flat turf and 45° turf anvils for front, front-boss and rear-boss impact locations. The results demonstrated EN1 and EN2 both had higher magnitude accelerations and shorter duration impacts than reconstructed real-world concussive impacts. Impacts to turf anvils, on the other hand, produced similar head kinematics compared to the reconstructed real-world concussive impacts. Additionally, this study demonstrated that helmeted impacts significantly decreased rotational kinematics and brain tissue response below what is associated with unhelmeted impacts for oblique falls. However, the head kinematics and brain tissue response associated with these helmeted falls were consistent with concussion, suggesting that scope exists to improve the capacity of equestrian helmets to protect against concussion.

Development of a test method for adult ice hockey helmet evaluation.

Ice hockey helmet standards have primarily been developed to reduce risk of traumatic brain injury (TBI). While severe TBI has become a rare event in ice hockey, concussion, a type of mild TBI, remains a common head injury. Concussions, in ice hockey result from a number of head impact events including, collisions, stick impacts, puck impacts, falls into the boards, impacts to the glass, and falls to the ice. Helmet testing methods need to represent the impact events creating concussions in ice hockey. The purpose of this research was to develop a helmet test protocol and performance metric for concussive impacts in ice hockey. A protocol using concussion impact parameters from published literature was created that used monorail and linear impactors to impact a helmeted Hybrid III headform. The linear and rotational acceleration time curves were then used to calculate brain tissue strain using the University College Brain Trauma Model. The proposed test protocols created kinematic responses that were representative of levels associated with concussion in ice hockey. Rotational velocity and rotational acceleration were both identified as useful performance metrics representing levels of risk for concussion.