Use of Brain Biomechanical Models for Monitoring Impact Exposure in Contact Sports

Head acceleration measurement sensors are now widely deployed in the field to monitor head kinematic exposure in contact sports. The wealth of impact kinematics data provides valuable, yet challenging, opportunities to study the biomechanical basis of mild traumatic brain injury (mTBI) and subconcussive kinematic exposure. Head impact kinematics are translated into brain mechanical responses through physics-based computational simulations using validated brain models to study the mechanisms of injury. First, this article reviews representative legacy and contemporary brain biomechanical models primarily used for blunt impact simulation. Then, it summarizes perspectives regarding the development and validation of these models, and discusses how simulation results can be interpreted to facilitate injury risk assessment and head acceleration exposure monitoring in the context of contact sports. Recommendations and consensus statements are presented on the use of validated brain models in conjunction with kinematic sensor data to understand the biomechanics of mTBI and subconcussion. Mainly, there is general consensus that validated brain models have strong potential to improve injury prediction and interpretation of subconcussive kinematic exposure over global head kinematics alone. Nevertheless, a major roadblock to this capability is the lack of sufficient data encompassing different sports, sex, age and other factors. The authors recommend further integration of sensor data and simulations with modern data science techniques to generate large datasets of exposures and predicted brain responses along with associated clinical findings. These efforts are anticipated to help better understand the biomechanical basis of mTBI and improve the effectiveness in monitoring kinematic exposure in contact sports for risk and injury mitigation purposes

Biomechanics and Injury Assessment of Head Impact Due to Falls

Head injury due to impact from falls represents a significant and growing problem. Due to an increasing incidence of fall related head injuries, there is significant concern regarding this important public health issue. Mitigation of head injuries due to falls requires a comprehensive understanding of the causes and the potential of head injuries in fall accidents. Injury prevention can include practices that promote fall reduction and development of high performance head protection devices. Therefore, to develop high performance protective headgear, a comprehensive database that provides the bounds and correlation between impact parameters is needed for estimating impact parameters based on fall conditions. This database is not currently available and there are currently no U.S. standards that exist specifically for design of protective headgear for falls. The aim of this dissertation was to fulfill the gap in the knowledge base that exists in this field by providing a database that gives an estimation of the head injury potential that may arise from falling and the bounds of the impact parameters; these parameters include force, peak linear and angular acceleration/velocity to the head due to an unprotected fall and prescribing reasonable criteria for design and evaluation of impact attenuation devices for falls. To ascertain these bounds—since it was not possible to assess the response of head impact due to human falling onto hard surfaces in the laboratory because of safety concerns—the pedestrian versions of a Hybrid III 5th percentile female and 50th percentile male anthropomorphic test dummy(ATD) were used. Several common fall scenarios were initiated from a frontal, sideward and backward orientation and the responses of the ATDs were quantified. A Vicon™ motion capture system was used to track the motion of the ATD during the fall. For verification, prior methods employed in other studies, including numerical simulations and cadaveric experiments were compared to the bounds obtained in this study. The effect of fall scenarios on head impact was also studied. In addition, in reconstruction of the real life fall incidents or head impact testing, some of the impact parameters are not available while the other impact parameters have been recorded or computed based upon eye-witness reports; video tape recorded or acquired sensor signals. Therefore, correlation between impact parameters were established and prediction intervals were obtained to provide bounds for estimation of the unavailable head impact parameters based on fall conditions and available impact parameters. These correlations can be used to develop simplified experimental procedures for testing of head protection devices and also improve real life fall incident reconstructions in forensic engineering. In addition, a concise review of head injury mechanisms and predictors was provided and head injury potentials in falls from diverse vantage points were assessed. Finally, the mass involved during head impact—the effective mass that expresses the contribution of the body during the event—was quantified and the effect of fall direction/type on the effective mass estimate was studied. The effective mass is a key parameter in the development of appropriate methodology to simulate falls more realistically. In summary, the studies performed for this dissertation dealt with different aspects of head impacts and injuries due to standing falls and provided further information on informed development of testing methods, standards, and how to more accurately reconstruct real life fall incidents and related head impacts

Comprehensive study of sex-based anatomical variations of human brain and development of sex-specific brain templates

The sex-based human brain structural variations alongside the necessity and development process for sex-specific brain templates were investigated in this study. Comparing magnetic resonance images of 500 female and 500 male subjects, no significant sex-based difference was observed for average cortical thickness, however, all the volumetric values, including the total brain volume (TBV) and major 19 brain regions, were found to be significantly different between females and males. Moreover, analyzing the fractional volume of the regions showed that these sex variations were not proportional to TBV for all regions. These findings underscore the importance of distinguishing the sex-based differences in human brain studies. While brain templates have been developed for general population and cohorts with the same characteristics such as race or age, there is a lack of sex-specific brain templates. To fill this gap and find a representative reference brain image for each sex, nonlinear templates were developed for female, male, and mixed population subjects. Next, a separate set of 109 female and 109 male brain images were used to evaluate the sex-specificity of the brain templates. It was observed that the female and male test subjects were registered to their sex-specific templates with the lowest amount of deformation/warping confirming better representativeness of the sex-specific templates for their target population. The findings of this study including the templates and the reported variations can be used in research involving sex dimorphic brain disorders, diseases, and/or injuries such as traumatic brain injury that is affected by the sex-based brain anatomical differences. Statement of significance: Human brain exhibits sex-based variation both in size and volumetric composition of different regions. Despite these differences, there is a paucity of sex-specific brain templates. Addressing this gap marks the significance of our study as briefly explained here. We have shown that differences in male and female brain go beyond simple scaling and the observation of regional differences that are not proportional to the sex-based total brain volume variations has motivated us to develop sex-specific templates. The representativeness and difference of these sex-specific templates were assessed by measuring the amount of required warping in nonlinear registration of test subjects to them. It was shown that registration of female and male subjects to their corresponding sex-specific template involved lower level of warping compared to their registration to their opposite sex or mixed population brain template

Multiple Head Rotations Result in Persistent Gait Alterations in Piglets

Multiple/repeated mild traumatic brain injury (mTBI) in young children can cause long-term gait impairments and affect the developmental course of motor control. Using our swine model for mTBI in young children, our aim was to (i) establish a reference range (RR) for each parameter to validate injury and track recovery, and (ii) evaluate changes in gait patterns following a single and multiple (5×) sagittal rapid non-impact head rotation (RNR). Gait patterns were studied in four groups of 4-week-old Yorkshire swine: healthy (n = 18), anesthesia-only sham (n = 8), single RNR injury (n = 12) and multiple RNR injury (n = 11). Results were evaluated pre-injury and at 1, 4, and 7 days post-injury. RR reliability was validated using additional healthy animals (n = 6). Repeated mTBI produced significant increases in gait time, cycle time, and stance time, as well as decreases in gait velocity and cadence, on Day One post-injury compared to pre-injury, and these remained significantly altered at Day Four and Day Seven post-injury. The gait metrics of the repeated TBI group also significantly fell outside the healthy RR on Day One, with some recovery by Day Four, while many remained altered at Day Seven. Only a bilateral decrease in hind stride length was observed at Day Four in our single RNR group compared to pre-injury. In sum, repeated and single sagittal TBI can significantly impair motor performance, and gait metrics can serve as reliable, objective, quantitative functional assessments in a juvenile porcine RNR TBI model

Using Serum Amino Acids to Predict Traumatic Brain Injury: A Systematic Approach to Utilize Multiple Biomarkers

Traumatic brain injury (TBI) can cause biochemical and metabolomic alterations in the brain tissue and serum. These alterations can be used for diagnosis and prognosis of TBI. Here, the serum concentrations of seventeen amino acids (AA) were studied for their potential utility as biomarkers of TBI. Twenty-five female, 4-week-old piglets received diffuse (n = 13) or focal (n = 12) TBI. Blood samples were obtained both pre-injury and at either 24-h or 4-days post-TBI. To find a robust panel of biomarkers, the results of focal and diffuse TBIs were combined and multivariate logistic regression analysis, coupled with the best subset selection technique and repeated k-fold cross-validation method, was used to perform a thorough search of all possible subsets of AAs. The combination of serum glycine, taurine, and ornithine was optimal for TBI diagnosis, with 80% sensitivity and 86% overall prediction rate, and showed excellent TBI diagnostic performance, with 100% sensitivity and 78% overall prediction rate, on a separate validation dataset including four uninjured and five injured animals. We found that combinations of biomarkers outperformed any single biomarker. We propose this 3-AA serum biomarker panel to diagnose mild-to-moderate focal/diffuse TBI. The systematic approaches implemented herein can be used for combining parameters from various TBI assessments to develop/evaluate optimal multi-factorial diagnostic/prognostic TBI metrics