Arena

Newsletter of the Boston University School of Medicine, Student American Medical Association (SAMA

Orientation of the Intercostal Muscle Fibers in the Human Rib Cage

Great improvement was achieved to protect vehicle occupants in case of a motor vehicle crashes thanks to the development of restraint systems such as seat belts and airbags . These systems increase the mechanical coupling between the human body and the vehicle to minimize the risk of severe injuries to the thorax and the head during a crash. As a result, they may induce injuries, such as rib fractures because of the loading applied to the thorax by the seat belt. Predict- ing and preventing injuries to the thorax is of particular interest as severe injuries occurred predominantly in the thorax in side impact (Welsh et al. 2009) and in elderly subjects. Significant efforts were put in the development of computational finite element models of the thorax to accurately predict the rib fractures created because of an impact (Li et al. 2010). While the mechanical response of the individual human ribs has been widely studied (Charpail et al. 2005; Kindig 2009), only few studies reported on the contribution of the inter- costal muscles (ICM) on the rib cage impact response (Vezin & Berthet 2009). Furthermore, computational studies designed to assess the con- tribution of the ICM in the thorax impact response had to face the lack of detailed description of the ICM structure such as their thickness, and their fiber orientation (Poulard & Subit 2015). Therefore, the goal of this study was to measure the orientation of the fibers in the ICM layers in the human thorax

Traumatic brain injury in pedestrian–vehicle collisions: Convexity and suitability of some functionals used as injury metrics

Background and Objective: Abrupt accelerations or decelerations can cause large strain in brain tissues and, consequently, different forms of Traumatic Brain Injury (TBI). In order to predict the effect of the accelerations upon the soft tissues of the brain, many different injury metrics have been proposed (typically, an injury metric is a real valued functional of the accelerations). The objective of this article is to make a formal and empirical comparison, in order to identify general criteria for reasonable injury metrics, and propose a general guideline to avoid ill-proposed injury metrics. Methods: A medium-size sample of vehicle-pedestrian collisions, from Post Mortem Human Subject (PMHS) tests, is analyzed. A statistical study has been conducted in order to determine the discriminant power of the usual metrics. We use Principal Component Analysis to reduce dimensionality and to check consistency among the different metrics. In addition, this article compares the mathematical properties of some of these functionals, trying to identify the desirable properties that any of those functionals needs to fulfill in order to be useful for optimization. Results: We have found a pair-wise consistency of all the currently used metrics (any two injury metrics are always positively related). In addition, we observed that two independent principal factors explain about 72.5% of the observed variance among all collision tests. This is remarkable because it indicates that despite high number of different injury metrics, a reduced number of variables can explain the results of all these metrics. With regard to the formal properties, we found that essentially all injury mechanisms can be accounted by means of scalable, differentiable and convex functionals (we propose to call minimization suitable injury metric to any metric having these three formal properties). In addition three useful functionals, usable as injury metrics, are identified on the basis of the empirical comparisons. Conclusions: The commonly used metrics are highly consistent, but also highly redundant. Formal minimal conditions of a reasonable injury metric have been identified. Future proposals of injury metrics can benefit from the results of this study.Peer ReviewedPostprint (author's final draft

Pediatric, adult and elderly bone material properties

Age dependence; Bone; Coupon; Full field strain measurements; Quasi-static and dynamic tensile testsPostprint (published version

The influence of impact speed on chest injury outcome in whole body frontal sled impacts

While the seatbelt restraint has significantly improved occupant safety, the protection efficiency still needs further enhance to reduce the consequence of the crash. Influence of seatbelt restraint loading on chest injury under 40 km/h has been tested and documented. However, a comprehensive profiling of the efficiency of restraint systems with various impact speeds has not yet been sufficiently reported. The purpose of this study is to analyse the effect of the seatbelt load-ings on chest injuries at different impact speeds utilizing a high bio-fidelity human body Finite Element (FE) model. Based on the whole-body frontal sled test configuration, the current simulation is setup using a substitute of Post-Mortem Human Subjects (PMHS). Chest injury outcomes from simulations are analysed in terms of design variables, such as seatbelt position parameters and collision speed in a full factorial experimental design. These outcomes are specifically referred to strain-based injury probabilities and four-point chest deflections caused by the change of the parameters. The results indicate that impact speed does influence chest injury outcome. The ribcage injury risk for more than 3 fractured ribs will increase from around 40 to nearly 100% when the impact speed change from 20 to 40 km/h if the seatbelt positioned at the middle-sternum of this study. Great injuries to the chest are mainly caused by the change of inertia, which indicates that chest injuries are greatly affected by the impact speed. Furthermore, the rib fracture risk and chest deflection are nonlin-early correlated with the change of the seatbelt position parameters. The study approach can serve as a reference for seatbelt virtual design. Meanwhile, it also provides basis for the research of chest injury mechanism

Comparison of kinematics of GHBMC to PMHS on the side impact condition

The goal of this study was to evaluate the biofidelity of the Global Human Body Models Consortium (GHBMC) human body model under a side impact loading condition with an airbag, and analyze the effect of initial position of the model on the response. Shaw et al. conducted side impact sled tests using three Post mortem human surrogates (PMHS) with impact speeds of 4.3 ± 0.1 m/s, and used a rigid wall boundary condition with an airbag mounted to the sled. The correlation between the PMHS and the GHBMC was evaluated using the CORA rating method. The rating ranged from 0.27 to 0.69 along the body regions on a scale in which a rating of 1.0 indicated a perfect correlation between the PMHS and the GHBMC. The pelvis and thorax region showed good correlation with those of the PMHS while the spinal regions did not. In addition, the roll and yaw angle of the initial position of the PMHS had an effect on the response of subjects. The result of this research indicated two points, that the GHBMC model should be validated focusing on the internal biofidelity of the model, and that the yaw and roll angle should be carefully controlled during a side impact test.Postprint (published version

THE KINEMATICS OF HEAD IMPACTS IN CONTACT SPORT: AN INITIAL ASSESSMENT OF THE POTENTIAL OF MODEL BASED IMAGE MATCHING

Model Based Image Matching (MBIM) has potential to assess three-dimensional linear and rotational motion patterns from multiple camera views of head impact events in contact sports. The goal of this study is to assess the accuracy of the MBlM method for estimating 6DOF head kinematics in a vehicle-cadaver impact scenario for which Vicon motion analysis data are available as an independent measure. A three camera view MBlM reconstruction yielded RMS errors between 0.14-0.26 mls for change in head linear velocities ranging from 0.56-5.70 m/s, and 0.27-1.38 rad/s for change in head angular velocities ranging from 6.1041 -90 rad/s. The results from this study indicate that the MBlM method is a useful approach for measuring the kinematics of head impacts in sport

Measuring the acceleration of a rigid body

Two methods to measure the six-degree-of-freedom acceleration of a point on a rigid body are presented. The first, referred to as the periphery scheme, makes use of three clusters of accelerometers mounted orthogonal to each other and coincident with the axes of the point. One of the clusters consists of the three accelerometers attached to a cube-shaped triaxial angular rate sensor (ARS). The second method, called the compact cube scheme, uses a single 3-accelerometer/ARS cluster that may be mounted anywhere on the rigid body. During impact tests with an instrumented rigid body, both methods produced measurements that were highly correlated near the time of peak acceleration. Whereas the compact cube scheme was more economical and easier to implement, the periphery scheme produced results that were less disrupted by instrument signal errors and noisy environments