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In situ Measures of Head Impact Acceleration in NCAA Division I Men's Ice Hockey: Implications for ASTM F1045 and Other Ice Hockey Helmet Standards
Abstract
Description
The latest volume in this comprehensive series enhances our understanding of both the injuries incurred in the game of ice hockey and of the techniques used to decrease the risk of these injuries.
Twenty-one peer-reviewed papers cover injury prevention and decreasing the risk of catastrophic injuries. Half of the papers in this book cover head and neck injuries, focusing on their analysis, prevention, and treatment of concussions.
The four approaches to achieve these objectives include
These papers were written by experts in their fields, including researchers in a diverse group of fields, including sports medicine, biokinetics, mechanical engineering, neuropsychology, sports litigation, and sports epidemiology.
Optimizing the protective capabilities of helmets is one of several methods of reducing brain injury risk in sports. This paper presents the experimental and analytical development of a hockey helmet evaluation methodology. The Summation of Tests for the Analysis of Risk (STAR) formula combines head impact exposure with brain injury probability over the broad range of 227 head impacts that a hockey player is likely to experience during one season. These impact exposure data are mapped to laboratory testing parameters using a series of 12 impact conditions comprised of three energy levels and four head impact locations, which include centric and non-centric directions of force. Injury risk is determined using a multivariate injury risk function that incorporates both linear and rotational head acceleration measurements. All testing parameters are presented along with exemplar helmet test data. The Hockey STAR methodology provides a scientific framework for manufacturers to optimize hockey helmet design for injury risk reduction, as well as providing consumers with a meaningful metric to assess the relative performance of hockey helmets.
This study was conducted to investigate differences in brain response due to frontal and lateral impacts based on a partially validated three-dimensional finite element model with all essential anatomical features of a human head. Identical impact and boundary conditions were used for both the frontal and lateral impact simulations. Intracranial pressure and localized shear stress distributions predicted from these impacts were analyzed. The model predicted higher positive pressures accompanied by a relatively large localized skull deformation at the impact site from a lateral impact when compared to a frontal impact. Lateral impact also induced higher localized shear stress in the core regions of the brain. Preliminary results of the simulation suggest that skull deformation and internal partitions may be responsible for the directional sensitivity of the head in terms of intracranial pressure and shear stress response. In previous experimental studies using subhuman primates, it was found that a lateral impact was more injurious than a frontal impact. In this study, shear stress in the brain predicted by the model was much higher in a lateral impact in comparison with a frontal impact of the same severity. If shear deformation is considered as an injury indicator for diffuse brain injuries, a higher shear stress due to a lateral impact indicate that the head would tend to have a decreased tolerance to shear deformation in lateral impact. More research is needed to further quantify the effect of the skull deformation and dural partitions on brain injury due to impacts from a variety of directions and at different locations.
The number of minor traumatic brain injury (mTBI), cerebral concussions, is increasing and cannot be eliminated by any kind of equipment. Prevention strategies, such as the introduction of "checking from behind" rules have become effective in decreasing the number of severe spinal injuries. A new "head checking" rule should reduce mTBI in the same way in the following years. Mouthguards should be mandatory as an effective device for the prevention of dental and orofacial injuries, as well as reducing the incidence and severity of mTBI. A new internet database system, the International Sports Injury System (ISIS) should improve epidemiological analysis of head, face, and spinal injuries worldwide. ISIS should provide an internationally compatible system for continuous monitoring of risk factors, protective effects of equipment, and protective effects of equipment and effects of changes in rules through the years.
Traumatic brain injuries constitute a significant portion of injury resulting from automotive collisions, motorcycle crashes, and sports collisions. Brain injuries not only represent a serious trauma for those involved but also place an enormous burden on society, often exacting a heavy economical, social, and emotional price. Development of intervention strategies to prevent or minimize these injuries requires a complete understanding of injury mechanisms, response and tolerance level. In this study, an attempt is made to delineate actual injury causation and establish a meaningful injury criterion through the use of the actual field accident data. Twenty-four head-to-head field collisions that occurred in professional football games were duplicated using a validated finite element human head model. The injury predictors and injury levels were analyzed based on resulting brain tissue responses and were correlated with the site and occurrence of mild traumatic brain injury (MTBI). Predictions indicated that the shear stress around the brainstem region could be an injury predictor for concussion. Statistical analyses were performed to establish the new brain injury tolerance level.
To measure and analyze head accelerations during American collegiate football practices and games.
A newly developed in-helmet 6-accelerometer system that transmits data via radio frequency to a sideline receiver and laptop computer system was implemented. From the data transfer of these accelerometer traces, the sideline staff has real-time data including the head acceleration, the head injury criteria value, the severity index value, and the impact location. Data are presented for instrumented players for the entire 2003 football season, including practices and games.
American collegiate football.
Thirty-eight players from Virginia Tech's varsity football team.
Accelerations and pathomechanics of head impacts.
: A total of 3312 impacts were recorded over 35 practices and 10 games for 38 players. The average peak head acceleration, Gadd Severity Index, and Head Injury Criteria were 32 g +/- 25 g, 36 g +/- 91 g, and 26 g +/- 64 g, respectively. One concussive event was observed with a peak acceleration of 81 g, a 267 Gadd Severity Index, and 200 Head Injury Criteria. Because the concussion was not reported until the day after of the event, a retrospective diagnosis based on his history and clinical evaluation suggested a mild concussion.
The primary finding of this study is that the helmet-mounted accelerometer system proved effective at collecting thousands of head impact events and providing contemporaneous head impact parameters that can be integrated with existing clinical evaluation techniques.
To determine the incidence and epidemiology of emergency department (ED)-attended mild traumatic brain injury (mTBI) in the US.
Secondary analysis of ED visits for mTBI in the National Hospital Ambulatory Medical Care Survey for 1998--2000.
MTBI defined by International Classification of Diseases, 9th Revision, Clinical Modification (ICD9-CM) codes for 'skull fracture', 'concussion', 'intracranial injury of unspecified nature' and 'head injury, unspecified'.
The average incidence of mTBI was 503.1/100000, with peaks among males (590/100000), American Indians/Alaska Natives (1,026/100000) and those <5 years of age (1,115.2/100000). MTBI incidence was highest in the Midwest region (578.4/10000) and in non-urban areas (530.9/100000) of the US. Bicycles and sports accounted for 26.4% of mTBI in the 5-14 age group.
The national burden of mTBI is significant and the incidence higher than that reported by others. Possible explanations are discussed. Bicycle and sports-related injuries are an important and highly preventable cause of mTBI underscoring the need to promote prevention programmes on a national level.
The objective of the present study was to analyze the effect of different loading directions following impact, and to evaluate existing global head injury criteria. Detailed and parameterized models of the adult human head were created by using the Finite Element Method (FEM). Loads corresponding to the same impact power were imposed in different directions. Furthermore, the Head Injury Criterion (HIC) and the recently proposed Head Impact Power (HIP) criterion were evaluated with respect to the relative motion between the skull and the brain, as well as the strain in the bridging veins. It was found that the influence of impact direction had a substantial effect on the intracranial response. The largest relative skull-brain motion and strain in the bridging veins occurred with the anterior-posterior (AP) and posterior-anterior (PA) rotational impulses. HIC was unable to predict consequences of a pure rotational impulse while HIP needed individual scaling coefficients for the different terms to account for difference in load direction. When using the proposed scaling procedure, a better prediction of subdural hematoma (SDH) was obtained. It is thus suggested that an evaluation of the synergistic terms is necessary to further improve the injury prediction. These variations should be considered when developing new head injury criteria.
The objective of this study was to characterize the risk of mild traumatic brain injury (MTBI) in living humans based on a large set of head impact data taken from American football players at the collegiate level. Real-time head accelerations were recorded from helmet-mounted accelerometers designed to stay in contact with the player's head. Over 27,000 head impacts were recorded, including four impacts resulting in MTBI. Parametric risk curves were developed by normalizing MTBI incidence data by head impact exposure data. An important finding of this research is that living humans, at least in the setting of collegiate football, sustain much more significant head impacts without apparent injury than previously thought. The following preliminary nominal injury assessment reference values associated with a 10% risk of MTBI are proposed: a peak linear head acceleration of 165 g, a HIC of 400, and a peak angular head acceleration of 9000 rad/s2.
Description
The latest volume in this series enhances our understanding of both the injuries incurred in the game of ice hockey and of the techniques used to decrease the risk of these injuries.
25 peer-reviewed papers cover:
• Injury Surveillance--discusses the injury surveillance system and the principles of ice hockey injury research.
• Protective Equipment--focuses on the certification of protective equipment for ice hockey in the U.S., and the designs and standards for various forms of ice hockey headgear.
• Spinal Injuries and Concussions--explores various aspects of these types of injuries, including care and transport of injured players and a three-decade perspective.
• Penalties, Injuries, and Pressures--examines psychosocial and psychological aspects of aggressive play, views and assessments of rule infractions and penalties, and liability issues facing the in-line skating industry.
This volume is a valuable resource for hockey equipment manufacturers, academic sports biomechanics, all hockey coaches and administrators, sports medicine physicians, and athletic trainers.
Description
The first book published on the historical and scientific aspects of safety in the sport of ice hockey. Contains 25 papers covering: injury rates in amateur, college, and professional hockey; risk factors, game rules and officiating; playing equipment, skates, sticks, protective types; playing facilities (indoor and outdoor) causative factors in catastrophic injuries; the role of standards in protective equipment for the head and face, and for skate blades and their effectiveness.
The ability of hockey helmets to limit localized pressure was examined by mounting selected samples of Canadian Standards Association (CSA) certified helmets onto a humanoid headform and subjecting them to single puck impacts to the left temporal area at three different velocities. The peak pressure on the headform was determined from Fuji pressure-sensitive film that was applied to the headform before impact. Peak headform acceleration and the severity index (SI) were also measured. For five of the six helmet models, the peak pressure was less than 15.0 MPa at 27.8 m/s, less than 16.0 MPa at 33.4 m/s, and less than 25/0 MPa at 38.9 m/s. In the remaining model, the largest peak pressure was 27.8 MPa at 38.9 m/s. None of the helmets tested was able to limit the localized pressure on the headform to below 3.1 MPa, the reported fracture tolerance of the temporoparietal area of the human skull. Peak headform accelerations were at or below 250 g for all helmets at 27. 8 and 33.4 m/s, but exceeded 275 g in four models at 38.9 m/s. SI values were all less than 800, indicating a concussive head injury risk of less than 2 to 5%. The SI and peak g measures were not useful for determining the focal injury risk caused by puck impacts suggesting that additional test procedures should be included in future certification standards.
A mathematical model for studying head protection in static is presented and its application to the design of ice hockey helmets is discussed. Static load and dynamic impact tests indicate that dynamic tests are to be preferred when estimating the stiffness of the materials used ns helmet liners. Solutions to the differential equations governing the linear motion of the head under a sideboard collision provide information regarding the thickness of the energy absorbing helmet liner and the tolerance level to which the helmet can be expected to perform. The model also provides a useful estimate of the angular velocity of the head imparted by the rebound from the sideboard. Although the helmet cannot prevent angular motion of the head, an estimate of the expected angular velocity may indicate that additional measures must be taken to prevent head injury from such angular motion. The study also indicates that the problem of providing head protection in ice hockey is of such magnitude that a helmet alone cannot be expected to provide total protection and additional modification to the playing environment must also be undertaken.
The head injury criterion (HIC) is currently the government-accepted head injury indicator. The HIC is not injury-specific, does not relate to injury severity, nor does it take into account variations in the brain mass or load direction. This report focuses on one type of inertial brain injury, diffuse axonal injury (DAI), and utilizes animal studies, physical model experiments, and analytical model simulations to determine the kinematics of DAI in the subhuman primate and to scale these results to man. A human injury tolerance for moderate to severe DAI, which includes the influences of rotational loads and brain mass, is proposed.
As part of the injury profylaxes in Denmark a questionnaire investigation was undertaken in 14 randomly chosen ice hockey teams--out of 266 players, 210 answered (79%). The injury incidence per player per 1000 hours was 4.7, i.e. 1.5 in training and 38.0 in match. Half of the injuries were localised to the head (28%) and lower extremities (27%), 19% to the upper extremities and 7% to the back. Of these 48% were contusions. Knee and elbow injuries were of longest duration. The necessity for increased shock absorption in helmets and barriers as well as built-in rotational and collateral stabilizers in the existing knee protectors for injury prophylaxis is stressed.
A new paradigm for cerebral concussion is proposed which is not refuted by the available clinical and experimental knowledge on head injuries. It is suggested that rotational components of acclerative trauma to the head produce a graded centripetal progression of diffuse cortical subcortical disconnection phenomena which is always maximal at the periphery and enhanced at sites of structural inhomogeneity. The translational components of such trauma are significant for the production of focal injuries only. In this hypothesis, the rostral brain stem (mesencephalon and caudal diencephalon) is the least vulnerable part of the brain and its involvement in the paralytic coma of head injury is always associated with significant injuries to more peripheral parts of the brain. Observations on traumatic amnesias, coma and lesion distribution after head injury are shown to be consistent with the predicted pattern of relative vulnerability of brain regions in head injury. The authors' hypothesis for cerebral concussion is defined as a graded set of clinical syndromes following head injury wherein increasing severity of disturbance in level and content of consciousness is caused by mechanically induced strains affecting the brain in a centripetal sequence of disruptive effect on function and structure. The effects of this sequence always begin at the surfaces of the brain in the mild cases and extend inwards to affect the diencephalic mesencephalic core at the most severe levels of trauma.
We review the relationship between science, testing standards, and helmet design to provide an understanding of how helmets protect the brain. Research describing the mechanisms of injury, resulting types of brain injuries, and characteristics of helmet protection are reviewed. The article is designed to describe the state of the relationship between science and helmet performance.
Accelerations of the head are the likely cause of concussion injury, but identifying the specific etiology of concussion has been difficult due to the lack of a valid animal or computer model. Contact sports, in which concussions are a rising health care concern, offer a unique research laboratory environment. However, measuring head acceleration in the field has many challenges including the need for large population sampling because of the relatively low incidence of concussions. We report a novel approach for calculating linear acceleration that can be incorporated into a head-mounted system for on-field use during contact sports. The advantages of this approach include the use of single-axis linear accelerometers, which reduce costs, and a nonorthogonal arrangement of the accelerometers, which simplifies the design criteria for a head-mounted and helmet compatible system. The purpose of this study was to describe the algorithm and evaluate its accuracy for measuring linear acceleration magnitude and impact location using computer simulation and experimental tests with various accelerometer configurations. A 10% error in magnitude and a 10 deg error in impact location were achieved using as few as six single-axis accelerometers mounted on a hemispherical headform.
Cerebral concussion is common in collision sports such as football, yet the chronic neurological effects of recurrent concussion are not well understood. The purpose of our study was to investigate the association between previous head injury and the likelihood of developing mild cognitive impairment (MCI) and Alzheimer's disease in a unique group of retired professional football players with previous head injury exposure.
A general health questionnaire was completed by 2552 retired professional football players with an average age of 53.8 (+/-13.4) years and an average professional football playing career of 6.6 (+/- 3.6) years. A second questionnaire focusing on memory and issues related to MCI was then completed by a subset of 758 retired professional football players (> or = 50 yr of age). Results on MCI were then cross-tabulated with results from the original health questionnaire for this subset of older retirees.
Of the former players, 61% sustained at least one concussion during their professional football career, and 24% sustained three or more concussions. Statistical analysis of the data identified an association between recurrent concussion and clinically diagnosed MCI (chi = 7.82, df = 2, P = 0.02) and self-reported significant memory impairments (chi = 19.75, df = 2, P = 0.001). Retired players with three or more reported concussions had a fivefold prevalence of MCI diagnosis and a threefold prevalence of reported significant memory problems compared with retirees without a history of concussion. Although there was not an association between recurrent concussion and Alzheimer's disease, we observed an earlier onset of Alzheimer's disease in the retirees than in the general American male population.
Our findings suggest that the onset of dementia-related syndromes may be initiated by repetitive cerebral concussions in professional football players.
Sports-related concussions result in 300,000 brain injuries in the United States each year. We conducted a study utilizing an in-helmet system that measures and records linear head accelerations to analyze head impacts in collegiate football. The Head Impact Telemetry (HIT) System is an in-helmet system with six spring-mounted accelerometers and an antenna that transmits data via radio frequency to a sideline receiver and laptop computer system. A total of 11,604 head impacts were recorded from the Virginia Tech football team throughout the 2003 and 2004 football seasons during 22 games and 62 practices from a total of 52 players. Although the incidence of injury data are limited, this study presents an extremely large data set from human head impacts that provides valuable insight into the lower limits of head acceleration that cause mild traumatic brain injuries.
To examine the mechanisms of injury for concussions in university football, ice hockey, and soccer.
Prospective analysis.
McGill University.
All athletes participating in varsity football, ice hockey, and soccer.
Athletes participating in university varsity football, ice hockey, and soccer were followed prospectively to determine the mechanisms of injury for concussions, whether certain mechanisms of injury causing concussions were more common in any of the three sports, whether different areas of the body seem to be more vulnerable to a concussion after contact, and whether these areas might be predisposed to higher grades of concussion after contact.
There were 69 concussions in 60 athletes over a 3-year period. Being hit in the head or helmet was the most common mechanism of injury for all 3 sports. The side/temporal area of the head or helmet was the most probable area to be struck, resulting in concussion for both football and soccer. When examining the body part or object delivering the concussive blow, contact with another player's helmet was the most probable mechanism in football.
The mechanisms of injury for concussions in football are similar to previously published research on professional football players. The mechanisms of injury for concussions in soccer are similar to past research on Australian rules football and rugby.
To compare the frequency and magnitude of head impacts between National Collegiate Athletic Association Division I and American high school football players. The long-term goal is to correlate impact forces with injury patterns, leading to improvements in protective headgear.
The helmets of football players at the University of Oklahoma (n = 40) and Casady High School (n = 16) were instrumented with the Head Impact Telemetry System (Simbex, Lebanon, NH). Data were collected for practices and games for the 2005 football season and were analyzed by player position and school. Player positions were separated into two groups (skill and line) for analysis. Two case studies of athletes who sustained a concussion are also presented.
A total of 54,154 impacts were recorded at the University of Oklahoma and 8326 at Casady High School. College players sustained high-level impacts greater than 98 g more frequently than high school players. The mean linear accelerations for the top 1, 2, and 5% of all impacts were also higher for college players (P < 0.02). Skill position players received 24.6% of all impacts and sustained an impact greater than 98 g once every 70 impacts. In contrast, linemen sustained the highest number of impacts, but most were relatively low-magnitude (20-30 g). Linemen sustained an impact greater than 98 g once every 125 impacts.
Differences in the frequency and magnitude of head acceleration after impact exist between a Division I college team and a high school team. Compared with linemen, skill position players typically sustain the highest-level impacts. Additional data collection and analysis are required to correlate concussion diagnosis with acceleration magnitude and impact location.
The purpose of our study was to investigate the association between prior head injury and the likelihood of being diagnosed with clinical depression among retired professional football players with prior head injury exposure.
A general health questionnaire, including information about prior injuries, the SF-36 (Short Form 36), and other markers for depression, was completed by 2552 retired professional football players with an average age of 53.8 (+/-13.4) yr and an average professional football-playing career of 6.6 (+/-3.6) yr. A second questionnaire focusing on mild cognitive impairment (MCI)-related issues was completed by a subset of 758 retired professional football players (50 yr and older).
Two hundred sixty-nine (11.1%) of all respondents reported having prior or current diagnosis of clinical depression. There was an association between recurrent concussion and diagnosis of lifetime depression (chi2=71.21, df=2, P<0.005), suggesting that the prevalence increases with increasing concussion history. Compared with retired players with no history of concussion, retired players reporting three or more previous concussions (24.4%) were three times more likely to be diagnosed with depression; those with a history of one or two previous concussions (36.3%) were 1.5 times more likely to be diagnosed with depression. The analyses controlled for age, number of years since retirement, number of years played, physical component score on the SF-36, and diagnosed comorbidities such as osteoarthritis, coronary heart disease, stroke, cancer, and diabetes.
Our findings suggest a possible link between recurrent sport-related concussion and increased risk of clinical depression. The findings emphasize the importance of understanding potential neurological consequences of recurrent concussion.
There exists a need to better understand the biomechanical forces associated with head impacts in American football. The purpose of this study was to investigate whether or not differences in head accelerations existed between different player positions and different event types in collegiate football. We also sought to identify whether or not any associations existed between high-magnitude impacts and location of head impacts.
We conducted a prospective field study in which accelerometers were embedded in the football helmets of 72 collegiate football players. Linear accelerations of all head impacts sustained over the course of the 2005 and 2006 National Collegiate Athletic Association football seasons were collected. One-way analyses of variance and chi tests of association assessed positional, event type, and location of head impact differences.
Football players consistently sustained head impacts between 21 and 23 g. Positional differences were identified within our sample. Impacts sustained during helmets-only practices were greater than those sustained in games or scrimmages. There was an association between position and high-magnitude impacts, as well as between high-magnitude impacts and location of head impact, with the likelihood of impacts to the top of the head much higher than those to the front, back, left, and right sides.
Less than 0.35% of impacts exceeding theoretical injury thresholds resulted in concussion. More injury data are required before any theoretical thresholds for injury can be confirmed. Coaches and sports medicine professionals should recognize that head impacts sustained in helmets-only practices are as severe as games or scrimmages; there seem to be no "light" days for football players.
The aims of this study were to quantify the sensitivity of various biomechanical measures (linear acceleration, rotational acceleration, impact duration, and impact location) of head impact to the clinical diagnosis of concussion in United States football players and to develop a novel measure of head impact severity combining these measures into a single score that better predicts the incidence of concussion.
On-field head impact data were collected from 449 football players at 13 organizations (n = 289,916) using in-helmet systems of six single-axis accelerometers. Concussions were diagnosed by medical staff and later associated with impact data. Principal component analysis and a weighting coefficient based on impact location were used to transform correlated head impact measures into a new composite variable, weighted principal component score (wPCS). The predictive power of linear acceleration, rotational acceleration, head injury criterion, and wPCS was quantified using receiver operating characteristic curves. The null hypothesis, that a measure was no more predictive than guessing, was tested (alpha = 0.05). In addition, receiver operating characteristic curves for wPCS and classical measures were directly compared to test the hypothesis that wPCS was more predictive of concussion than were classic measures (alpha = 0.05).
When all of the impacts were considered, every biomechanical measure evaluated was statistically more predictive of concussion than guessing (P < 0.005). However, for the top 1 and 2% of impacts based on linear acceleration, a subset that consisted of 82% of all diagnosed concussions, only wPCS was significantly more predictive of concussion than guessing (P < 0.03); when compared with each other, wPCS was more predictive of concussion than were classical measures for the top 1 and 2% of all of the data (P < 0.04).
A weighted combination of several biomechanical inputs, including impact location, is more predictive of concussion than a single biomechanical measure. This study is the first to the authors' knowledge to quantify improvements in the sensitivity of a biomechanical measure to incidence of concussion when impact location is considered.
The Relationship between Helmet Standards and Head Protectors Safety in Ice Hockey
- Hoshizaki
NIH Consensus Development Panel on Rehabilitation of Persons with Traumatic Brain Injury, “Rehabilitation of Persons with Traumatic Brain Injury
Hockey Headgear and the Adequacy of Current Design Standards
- Halstead
Concussion in Professional Football: Reconstruction of Game Impacts and Injuries
- E J Pellman
- D C Viano
- A M Tucker
- I R Casson
- J F Waeckerle
3-D Anatomic Brain Model of Relating Cortical Strains to Automotive Crash Loadings
- F Dimasi
- J Marcus
- R H Eppinger