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Illustration of the biomechanics of an oblique impact (lower), compared to a corresponding perpendicular one (upper), when impacted against the same padding using an identical initial velocity of 6.7 m/s. Maximum principal strain (Green-Lagrange) at maximum for the brain are illustrated together with the maximum von Mises stress for the skull bone. Parts of the figure are modified from Kleiven (2007a).
Source publication
Injury statistics have found the most common accident situation to be an oblique impact. An oblique impact will give rise to both linear and rotational head kinematics. The human brain is most sensitive to rotational motion. The bulk modulus of brain tissue is roughly five to six orders of magnitude larger than the shear modulus so that for a given...
Similar publications
Mild traumatic brain injury (mTBI, also known as concussion) caused by the head impact is a crucial global public health problem, but the physics of mTBI is still unclear. During the impact, the rapid movement of the head injures the brain, so researchers have been endeavoring to investigate the relationship between head kinematic parameters (e.g.,...
Citations
... In this research, we employed BrIC, HIC, and MPS as our TBI metrics. HIC, focusing solely on linear acceleration and overlooking rotational brain motion, fails to capture the brain's response to rotational loading, especially its tendency to deform in shear during impact [26]. In contrast, BrIC, derived from finite element head-neck models, correlates angular velocity induced by impact to brain strain, offering a more comprehensive understanding of TBI. ...
Purpose
This study aimed to investigate the role of neck muscle activity and neck damping characteristics in traumatic brain injury mechanisms.
Methods
We used a previously validated head-neck finite element model, incorporating various components such as scalp, skull, cerebrospinal fluid, brain, neck muscles, ligaments, cervical vertebrae, and intervertebral discs. Loading conditions included a golf ball impact NBDL linear acceleration and Zhang’s linear/rotational accelerations. Three muscle activation levels and variations in neck damping (viscoelastic intervertebral discs) were examined. Injury estimation employed Head Injury Criterion, Brain Injury Criterion, and maximum principal strain.
Results
In the NBDL acceleration scenario, increasing neck muscle activation consistently reduced HIC and BrIC values, with the most significant decrease occurring from no activation to medium-low activation. Neck damping had a moderate mitigating effect on HIC. The mean MPS decreased modestly with muscle activation, more substantially in the occipital region, and neck damping reduced MPS. In the Zhang scenario, HIC, BrIC, and MPS exhibited similar trends. Damping consistently decreased HIC and BrIC values. Golf ball impact scenarios showed increased risk of TBI, but higher muscle activation and neck damping reduced this risk. MPS analysis revealed nuanced impacts across brain regions, with neck damping showing substantial influence in the occipital region.
Conclusion
Our study underscores the pivotal role of neck muscle activation and damping in mitigating TBIs by countering impact forces. Our approach holds promise for advancing effective TBI prevention and protection strategies across diverse contexts.
... It is well known in the blunt impact literature (e.g., (Margulies et al., 1990;Rowson et al., 2012a;Kleiven, 2013; Wright et al., 2013;Ji et al., 2014;Zhao and Ji, 2016;Hernandez et al., 2019)) that acceleration and ICP of the head play an important role in causing mild and moderate brain injuries. However, data regarding head acceleration, ICP, and associated injuries is sparse in ballistic impact literature. ...
Behind helmet blunt trauma is a significant health concern in modern warfare. The ballistic response of the human head under ballistic impact is highly sought. Towards this end, we conducted ballistic experiments on three different headforms. The following headforms were considered: a) National Institute of Justice based rigid headform, b) Hybrid-III based flexible headform, and c) head model based headform. Headforms b, c were assembled with the Hybrid-III neck. An advanced combat helmet was fitted to the headforms. Helmet-head assembly was subjected to a 9 mm × 19 mm full metal jacket projectile having velocities of 430 ± 15 m/s. The response of the head surrogate in the front, back, side, and crown orientations was studied. Back face deformation (BFD), head kinematics, and intracranial pressures in headforms were measured. In addition, equivalent stress and maximum principal strain in the brain were obtained using concurrent finite element simulations. Results suggest that both local (i.e., due to the localized crushing of the helmet) and global (i.e., due to the bulk motion of the helmet-head parenchyma) responses were dominant under investigated ballistic impacts. Further, the type of the headform affected the biomechanical response. As compared to the rigid headform, a statistically significant increase in head kinematics was observed with the flexible headforms; changes in BFD were statistically insignificant. The orientation dependent responses have been observed. Overall, these results provide novel insights regarding the ballistic response of the headforms with the combat helmet and underscore critical considerations during the ballistic evaluation of helmets.
... This study concluded differences in soccer ball characteristics can influence dynamic acceleration head response 26 . While these acceleration measures were used in previous studies to quantify the magnitude of impact, finite element modelling of the brain used to calculate tissue strain is considered a more representative measure of brain trauma than head acceleration or velocity [20][21][22][23][24][25][26][27][28][29][30] . In addition, the velocities of the impacts in previous research were lower than those typically measured during gameplay, which limits their applicability to the range of headers players experience 20,[25][26][27]31,32 . ...
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.
... The brain is sensitive to shear deformation, and rotational acceleration of the head is generally associated with shear forces applied to the brain (Gennarelli et al. 1982;Chatelin et al. 2010;Post and Blaine Hoshizaki 2015). Shear deformations induced by rapid rotational motion of the head are hypothesized to be a primary mechanism of diffuse brain injury (e.g., concussion), while linear acceleration is typically associated with focal injuries (Meaney and Smith 2011;Kleiven 2013). A potential explanation for the observed difference in relationship between practices and games is variance in the intensity and focus of players between practice and game environments. ...
... head motion (Kleiven 2013;Post and Blaine Hoshizaki 2015); therefore, absorbing more head impact energy as translational energy instead of rotational energy may be beneficial for mitigating brain injury risk. Future research should consider further investigation of the proportion of rotational and translation head motion occurring within an individual impact. ...
... Furthermore, impacts to the face can not only result in contact forces exceeding the fracture tolerance of facial skeleton, but also generate a moment causing rotation of the head. Rotational motion is the primary injury mechanism for most traumatic brain injuries [22]. We previously showed in experimental tests and a numerical simulation that an impact to the lower face can generate a rapid and large change in head rotation [23]. ...
Current bicycle helmet standards require impact testing mostly covering cranial or skull vault. Bicyclists are exposed to impacts to the face causing facial and basilar skull fractures, and soft tissue injuries, in addition to traumatic brain injuries. We aim to describe patterns and frequencies of craniofacial injuries grouped by anatomical and injury sites to inform new test method development in future bicycle helmet standards and subsequently promote protective designs. We analysed fully reconstructed crashes involving a bicycle from the German In-Depth Accident Study (GIDAS), crash years 2010-2022. The type and location of an injury was determined through the Abbreviated Injury Scale (2015 version), a GIDAS-own variable, and free-text information. We found that a substantial portion of craniofacial injuries were to the face for both helmeted and unhelmeted bicyclists. Facial injuries shifted from the upper face to the mid-and lower face when a helmet was worn. We identified the mid-face as the most prominent region for improving bicycle helmet safety. Hence, a new test method with an extended test area covering mid-and lower face is recommended and injury risk to commonly fractured facial bones should be assessed in future standards. Protective designs appear technically feasible: A visor in connection with a chin guard, or novel concepts using inflatable technology, can improve bicycle helmet designs for facial impact protection and could be assessed in future standards.
... Linear and rotational head accelerations influence brain injury risk [9,22,23,28,29], and an emphasis on reducing rotational acceleration has driven new helmet design features. Bike helmet manufacturers have sought to decrease concussion risk by reducing the head's rotational acceleration upon impact using different rotation-mitigating technologies. ...
Dummy headforms used for impact testing have changed little over the years, and frictional characteristics are thought not to represent the human head accurately. The frictional interface between the helmet and head is an essential factor affecting impact response. However, few studies have evaluated the coefficient of friction (COF) between the human head and helmet surface. This study's objectives were to quantify the human head's static and dynamic COF and evaluate the effect of biological sex and hair properties. Seventy-four participants slid their heads along a piece of helmet foam backed by a fixed load cell at varying normal force levels. As normal force increased, static and dynamic human head COF decreased following power-law curves. At 80 N, the static COF is 0.32 (95% CI 0.30-0.34), and the dynamic friction coefficient is 0.27 (95% CI 0.26-0.28). Biological sex and hair properties were determined not to affect human head COF. The COFs between the head and helmet surface should be used to develop more biofidelic head impact testing methods, define boundary conditions for computer simulations, and aid decision-making for helmet designs.
... In that study, the peak neck force that resulted in basilar skull fractures was in the range of 2.74 to 4.72 kN. The pass/fail criteria in current helmet standards use peak head linear acceleration and HIC, which are associated with skull fracture or contusion (secondary to skull fracture); they do not measure rotational head kinematics, which are a better predictor for traumatic brain injury risk (Kleiven, 2013(Kleiven, , 2007. Furthermore, the local response of the brain, but not the global head kinematics, is intimately related to injury (King et al., 2003). ...
Objective:
Two-wheeler riders frequently sustain injuries to the head and face in real-world crashes, including traumatic brain injury, basilar skull fracture, and facial fracture. Different types of helmets exist today, which are recognized as preventing head injuries in general; however, their efficacy and limitations in facial impact protection are underexplored. Biofidelic surrogate test devices and assessment criteria are lacking in current helmet standards. This study addresses these gaps by applying a new, more biofidelic test method to evaluate conventional full-face helmets and a novel airbag-equipped helmet design. Ultimately, this study aims to contribute to better helmet design and testing standards.
Methods:
Facial impact tests at two locations, mid-face and lower face, were conducted with a complete THOR dummy. Forces applied to the face and at the junction of the head and neck were measured. Brain strain was predicted by a finite element head model taking both linear and rotational head kinematics as input. Four helmet types were evaluated: full-face motorcycle and bike helmets, a novel design called a face airbag (an inflatable structure integrated into an open-face motorcycle helmet), and an open-face motorcycle helmet. The unpaired, two-sided student's t-test was performed between the open-face helmet and the others, which featured face-protective designs.
Results:
A substantial reduction in brain strain and facial forces was found with the full-face motorcycle helmet and face airbag. Upper neck tensile forces increased slightly with both full-face motorcycle (14.4%, p >.05) and bike helmets (21.7%, p =.039). The full-face bike helmet reduced the brain strain and facial forces for lower-face impacts, but not for mid-face impacts. The motorcycle helmet reduced mid-face impact forces while slightly increasing forces in the lower face.
Significance of results:
The chin guards of full-face helmets and the face airbag protect by reducing facial load and brain strain for lower face impact; however, the full-face helmets' influence on neck tension and increased risk for basilar skull fracture need further investigation. The motorcycle helmet's visor re-directed mid-face impact forces to the forehead and lower face via the helmet's upper rim and chin guard: a thus-far undescribed protective mechanism. Given the significance of the visor for facial protection, an impact test procedure should be included in helmet standards, and the use of helmet visors promoted. A simplified, yet biofidelic, facial impact test method should be included in future helmet standards to ensure a minimum level of protection performance.
... Rapid deceleration predisposes to inertial injuries. Linear acceleration predisposes to rupturing of bridging veins (subdural hematomas), while angular acceleration does so to deeper cerebral structures (soaring hemorrhagic foci) [81], [82]. Cutting forces at the edges of hypothetical brain layers caused by angular acceleration led to breaking of axonal connections, which results in DAI. ...
A motorcycle or moped helmet is currently mandatory, and provides basic protection to the user of a motor-powered two-wheeler against the possible consequences of a road accident.
... King et al. estimated the average amateur rugby player can expect 77 impacts per game [70]. Many of these impacts are low impact, whereas large linear forces, such as one causing a skull fracture, is not necessarily associated with TBI [71]. Moreover, multiple studies show the tackle as the primary concussion mechanism in gameplay [68,72] and that lowering tackle height does not decrease concussion incidence [73,74]. ...
Objectives
To review the rate of soft-shell headgear use in rugby union, consumer knowledge of the protection potential of soft-shell headgear, incidence of concussion reported in rugby headgear studies, and the capacity of soft-shell headgear to reduce acceleration impact forces.
Design
A systematic search was conducted in July and August 2021 using the databases SPORT Discus, PubMed, MEDLINE, CINAHL (EBSCO), Scopus, and Science Direct. The review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The protocol for this systematic review was registered on PROSPERO (registration number: CRD42021239595).
Outcome measures
Rates of headgear use, reports of estimated protection of headgear against head injury, incidence of concussion and magnitude of impact collisions with vs. without headgear, impact attenuation of headgear in lab studies.
Results
Eighteen studies were identified as eligible: qualitative (N = 4), field (N = 7), and lab (N = 7). Qualitative studies showed low rates of headgear use and varying understanding of the protection afforded by headgear. Field studies showed negligible association of headgear use with reduced impact magnitude in headgear vs. non-headgear cohorts. Lab studies showed increased energy attenuation for thicker headgear material, poorer performance of headgear after repetitive impacts and increased drop heights, and promising recent results with headgear composed of viscoelastic polymers.
Conclusions
Rates of adoption of soft-shell headgear remain low in rugby and any association between its use and reduction in acceleration impact forces remains unclear. Lab results indicating improved impact attenuation need to be validated in the field. Further headgear-related research is needed with youth and female rugby players.
... Linear acceleration is the established injury mechanism for certain head injuries, such as skull fracture and other focal pathologies (such as extradural haematoma secondary to skull fracture). 54,73 However, both normal and oblique impacts induce head rotation, which is known to be a key mechanism of several distinct types of head injury, such as diffuse axonal injury. 38,39,51,54 Hence, it is necessary for standards to include rotational head kinematics in addition to linear acceleration. ...
... 54,73 However, both normal and oblique impacts induce head rotation, which is known to be a key mechanism of several distinct types of head injury, such as diffuse axonal injury. 38,39,51,54 Hence, it is necessary for standards to include rotational head kinematics in addition to linear acceleration. This inclusion must be underpinned by how severely and frequently cyclists sustain injuries caused by rotational motion of the head. ...
... The inclusion of both linear and rotational kinematics is guided by field knowledge of brain injury biomechanics. 54 The testing protocols of rating methods are developed to best assess protection capabilities and performance of helmets in realistic impact scenarios, with parameter selections based on the best available knowledge of real-world impacts and injuries. Our knowledge of cyclist head impact conditions continues to develop with the emergence of new research. ...
Head injuries are common for cyclists involved in collisions. Such collision scenarios result in a range of injuries, with different head impact speeds, angles, locations, or surfaces. A clear understanding of these collision characteristics is vital to design high fidelity test methods for evaluating the performance of helmets. We review literature detailing real-world cyclist collision scenarios and report on these key characteristics. Our review shows that helmeted cyclists have a considerable reduction in skull fracture and focal brain pathologies compared to non-helmeted cyclists, as well as a reduction in all brain pathologies. The considerable reduction in focal head pathologies is likely to be due to helmet standards mandating thresholds of linear acceleration. The less considerable reduction in diffuse brain injuries is likely to be due to the lack of monitoring head rotation in test methods. We performed a novel meta-analysis of the location of 1809 head impacts from ten studies. Most studies showed that the side and front regions are frequently impacted, with one large, contemporary study highlighting a high proportion of occipital impacts. Helmets frequently had impact locations low down near the rim line. The face is not well protected by most conventional bicycle helmets. Several papers determine head impact speed and angle from in-depth reconstructions and computer simulations. They report head impact speeds from 5 to 16 m/s, with a concentration around 5 to 8 m/s and higher speeds when there was another vehicle involved in the collision. Reported angles range from 10° to 80° to the normal, and are concentrated around 30°–50°. Our review also shows that in nearly 80% of the cases, the head impact is reported to be against a flat surface. This review highlights current gaps in data, and calls for more research and data to better inform improvements in testing methods of standards and rating schemes and raise helmet safety.
