A novel repetitive head impact exposure measurement tool differentiates player position in National Football League.

American-style football participation poses a high risk of repetitive head impact (RHI) exposure leading to acute and chronic brain injury. The complex nature of symptom expression, human predisposition, and neurological consequences of RHI limits our understanding of what constitutes as an injurious impact affecting the integrity of brain tissue. Video footage of professional football games was reviewed and documentation made of all head contact. Frequency of impact, tissue strain magnitude, and time interval between impacts was used to quantify RHI exposure, specific to player field position. Differences in exposure characteristics were found between eight different positions; where three unique profiles can be observed. Exposure profiles provide interpretation of the relationship between the traumatic event(s) and how tissue injury is manifested and expressed. This study illustrates and captures an objective measurement of RHI on the field, a critical component in guiding public policy and guidelines for managing exposure.

Could a Compliant Foam Anvil Characterize the Biofidelic Impact Response of Equestrian Helmets?

The performance of equestrian helmets to protect against brain injuries caused by fall impacts against compliant surfaces such as turf has not been studied widely. We characterize the kinematic response of simulated fall impacts to turf through field tests on horse racetracks and laboratory experiments. The kinematic response characteristics and ground stiffness at different going ratings (GRs) (standard measurement of racetrack condition) were obtained from 1 m and 2 m drop tests of an instrumented hemispherical impactor onto a turf racetrack. The "Hard" rating resulted in higher peak linear accelerations and stiffness, and shorter impact durations than the "Soft" and "Heavy" ratings. Insignificant differences were found among the other GRs, but a strong overall relationship was evident between the "going rating" and the kinematic response. This relationship was used to propose a series of three synthetic foam anvils as turf surrogates in equestrian falls corresponding to ranges of GRs of (i) heavy-soft (H-S), (ii) good-firm (G-F), and (iii) firm-hard (F-H). Laboratory experiments consisted of a helmeted headform being dropped onto natural turf and the turf surrogate anvils using a monorail drop rig. These experiments revealed that the magnitudes and durations of the linear and rotational accelerations for helmeted impacts to turf/turf surrogates were similar to those in concussive sports falls and collisions. Since the compliance of an impacted surface influences the dynamic response of a jockey's head during a fall impact against the ground, it is important that this is considered during both accident reconstructions and helmet certification tests.

Concussive and subconcussive brain trauma: the complexity of impact biomechanics and injury risk in contact sport.

Head impacts that transfer mechanical energy to the skull and create brain injuries have unique dynamic responses and brain tissue trauma characteristics. The magnitude of the impact energy and how it is transmitted creates three-dimensional linear and rotational accelerations of the head, resulting in unique strains on brain tissue. Biomechanical investigations of head injuries in contact sports have historically focused on attenuating energy transfer to the skull and brain. Typically, severe life-threatening events are caused by high-energy impact events that result in anatomic damage. Protective equipment attenuates energy transmission to neural tissues to decrease the risk of structural damage. In addition to reducing risk of skull fracture, helmets work by increasing impact compliance, to decrease the magnitude of the head's dynamic response and increase the duration of the event. This strategy helps prevent severe traumatic brain injuries and shifts the risk to concussion and repetitive head impact exposure. Metabolic, cellular, and physiologic responses characterize cumulative brain trauma that may manifest years later. Relying on the presence of symptoms to establish injury is subjective and limited in capturing the risks associated with neural tissue trauma. To more effectively capture brain injury risks in contact sports, we present the concept of brain trauma profiling, involving impact magnitude, frequency, interval, and duration of exposure. Brain trauma profiling captures and describes the cumulative and acute trauma-associated injury risks unique to each sport, level of play, and player position.

Peak linear and rotational acceleration magnitude and duration effects on maximum principal strain in the corpus callosum for sport impacts.

Concussion has been linked to the presence of injurious strains in the brain tissues. Research investigating severe brain injury has reported that strains in the brain may be affected by two parameters: magnitude of the acceleration, and duration of that acceleration. However, little is known how this relationship changes in terms of creating risk for brain injury for magnitudes and durations of acceleration common in sporting environments. This has particular implications for the understanding and prevention of concussive risk of injury in sporting environments. The purpose of this research was to examine the interaction between linear and rotational acceleration and duration on maximum principal strain in the brain tissues for loading conditions incurred in sporting environments. Linear and rotational acceleration loading curves of magnitudes and durations similar to those from impact in sport were used as input to the University College Brain Trauma Model and maximum principal strain (MPS) was measured for the different curves. The results demonstrated that magnitude and duration do have an effect on the strain incurred by the brain tissue. As the duration of the acceleration increases, the magnitude required to achieve strains reflecting a high risk of concussion decreases, with rotational acceleration becoming the dominant contributor. The magnitude required to attain a magnitude of MPS representing risk of brain injury was found to be as low as 2500rad/s2 for impacts of 10-15ms; indicating that interventions to reduce the risk of concussion in sport must consider the duration of the event while reducing the magnitude of acceleration the head incurs.

Evaluation of the protective capacity of baseball helmets for concussive impacts.

The purpose of this research was to examine how four different types of baseball helmets perform for baseball impacts when performance was measured using variables associated with concussion. A helmeted Hybrid III headform was impacted by a baseball, and linear and rotational acceleration as well as maximum principal strain were measured for each impact condition. The method was successful in distinguishing differences in design characteristics between the baseball helmets. The results indicated that there is a high risk of concussive injury from being hit by a ball regardless of helmet worn.

Rotational acceleration, brain tissue strain, and the relationship to concussion.

The mechanisms of concussion have been investigated by many researchers using a variety of methods. However, there remains much debate over the relationships between head kinematics from an impact and concussion. This review presents the links between research conducted in different disciplines to better understand the relationship between linear and rotational acceleration and brain strains that have been postulated as the root cause of concussion. These concepts are important when assigning performance variables for helmet development, car design, and protective innovation research.

Characterization of persistent concussive syndrome using injury reconstruction and finite element modelling.

Concussions occur 1.7 million times a year in North America, and account for approximately 75% of all traumatic brain injuries (TBI). Concussions usually cause transient symptoms but 10 to 20% of patients can have symptoms that persist longer than a month. The purpose of this research was to use reconstructions and finite element modeling to determine the brain tissue stresses and strains that occur in impacts that led to persistent post concussive symptoms (PCS) in hospitalized patients. A total of 21 PCS patients had their head impacts reconstructed using computational, physical and finite element methods. The dependent variables measured were maximum principal strain, von Mises stress (VMS), strain rate, and product of strain and strain rate. For maximum principal strain alone there were large regions of brain tissue incurring 30 to 40% strain. This large field of strain was also evident when using strain rate, product of strain and strain rate. In addition, VMS also showed large magnitudes of stress throughout the cerebrum tissues. The distribution of strains throughout the brain tissues indicated peak responses were always present in the grey matter (0.481), with the white matter showing significantly lower strains (0.380) (p<0.05). The impact conditions of the PCS cases were severe in nature, with impacts against non-compliant surfaces (concrete, steel, ice) resulting in higher brain deformation. PCS biomechanical parameters were shown to fit between those that have been shown to cause transient post concussive symptoms and those that lead to actual pathologic damage like contusion, however, values of all metrics were characterized by large variance and high average responses. This data supports the theory that there exists a progressive continuum of impacts that lead to a progressive continuum of related severity of injury from transient symptoms to pathological damage.

The influence of acceleration loading curve characteristics on traumatic brain injury.

To prevent brain trauma, understanding the mechanism of injury is essential. Once the mechanism of brain injury has been identified, prevention technologies could then be developed to aid in their prevention. The incidence of brain injury is linked to how the kinematics of a brain injury event affects the internal structures of the brain. As a result it is essential that an attempt be made to describe how the characteristics of the linear and rotational acceleration influence specific traumatic brain injury lesions. As a result, the purpose of this study was to examine the influence of the characteristics of linear and rotational acceleration pulses and how they account for the variance in predicting the outcome of TBI lesions, namely contusion, subdural hematoma (SDH), subarachnoid hemorrhage (SAH), and epidural hematoma (EDH) using a principal components analysis (PCA). Monorail impacts were conducted which simulated falls which caused the TBI lesions. From these reconstructions, the characteristics of the linear and rotational acceleration were determined and used for a PCA analysis. The results indicated that peak resultant acceleration variables did not account for any of the variance in predicting TBI lesions. The majority of the variance was accounted for by duration of the resultant and component linear and rotational acceleration. In addition, the components of linear and rotational acceleration characteristics on the x, y, and z axes accounted for the majority of the remainder of the variance after duration.