(E-197) Development and Validation of Inverted Head Form Orientation for Helmet Testing Using a Pneumatic Linear Impact System

Introduction:: American Football is one of the most popular sports in the country and continues to encourage the involvement of younger athletes. Unfortunately, American Football remains one of the leading causes of concussions in sports participation and affects approximately 4 million people each year [1][2]. Concussions are a growing concern in public health, especially in athletics, and the clinical implications of head injuries have become a more important and publicized entity. Therefore, the need for increased research in equipment safety, concussion risk, and brain-impact mechanics is imperative. Understanding the underlying mechanisms that cause concussions in response to impacts is critical for the diagnosis, care and treatment of patients, and the evaluation of sports headgear and design. Current concussion treatment and research has been aimed at the acute effects of the injury itself, diagnostic tools, and return-to-play decision making. Less research has examined how impacts affect the brain tissue as a structure [1]. During a concussive impact, brain acceleration creates relative motion at the brain-skull interface producing pressure and shear strain within brain tissue [3]. Cadaveric testing to study this phenomenon has not been performed in over 40 years. Therefore, we propose to use modern laboratory testing systems and instrumentation to quantify brain-skull impact mechanics by employing the use of cadaveric specimen. To do this, the specimen must be oriented invertedly to allow perfusion of the head by gravity. This study focuses on the development and validation of a fixture that allows testing of an inverted specimen to use in helmet testing.




Materials and Methods::
The Helmet Test Protocol developed by Biocore was used to aid in the development of a testing method that allows the validation of a new fixture that allows for testing of inverted specimen. A Cadex Linear Impactor was used in combination with a Hybrid III 50^th percentile male head form with a coplanar 6aɷ accelerometer array (2000 g, DTS; 18k deg/sec, DTS; 2000 g, Endevco) fixed at the head form center of gravity to measure head kinematics. This system will be used to validate that the inverted orientation is equivalent to the typical upright orientation. The commonly used upright fixture and the inverted fixture is shown in Figure 1.a and Figure 1.b, respectively. The test method consists of five bare head impacts at three speeds (5.5 m/s, 7.5 m/s, and 9.3 m/s) and at six different locations per the Helmet Test Protocol. This complete test method was executed using the common orientation and the inverted orientation. The variance in maximum resultant angular velocity, maximum resultant linear acceleration, and maximum resultant rotational acceleration was then used to ensure the orientations will produce similar results to confirm testing compliance.




Results, Conclusions, and Discussions::
Currently, testing has only been completed at two locations: the side location and the facemask central oblique (FMCO) location. In the next coming months, testing will be concluded at the other four locations. The maximum resultant angular velocity, maximum resultant linear acceleration, and maximum resultant rotational acceleration values generated from the 5.5 m/s bare head impacts for each orientation at the two impact locations are shown in Figure 1.c. All values for the upright orientation show to be in good agreement with the inverted orientation which confirms that the two fixtures produce similar data. Current helmet testing entails the use of synthetic head models consisting of a solid vinyl head form with internal sensors to detect head accelerations. The Hybrid III head form is a popular model that is used for the Helmet Test Protocol and many more helmet testing methods. Although these surrogate models have been widely adopted because of their durability, adaptability, ease-of-use, and non-biohazardous status, they cannot accurately represent a human head due to the lack of anatomical features, biological precision, and materials [4]. Doing this validation will inform our understanding of the experimental limitations of the commonly used Hybrid III head versus a cadaveric specimen.



The results from this study allow us to conclude that testing may be done in the inverted orientation as it is shown to be equivalent to the commonly used upright orientation. This inverted orientation is necessary for cadaveric testing to allow for perfusion of the head, which permits the proper environment and pressure for the brain ensuring biofidelity. The cadaveric testing following this study will look to highlight the experimental importance of maintaining biofidelity with cadaveric specimens that may be missing when impacting the Hybrid III head form. Doing this research will provide not only the American Football community, but vehicle safety, combat safety and other sports industry communities with key experimental research that has the potential to develop more efficient testing methods, a more accurate Hybrid III head form, and better helmet designs.






Acknowledgements (Optional): :
Thanks to the Clemson Department of Bioengineering and the Clemson Department of Food, Nutrition, and Packaging Science for support of this study and the Robert Brooks Sports Science Institute for research funding.




References (Optional): :
[1] Broglio, S. P., Annals of Biomedical Engineering, 2011, 40(1), 37–46. [2] Laker, S. R., PM&R, 2011, 3, S354–S358. [3] Rowson, S., Sports Medicine and Arthroscopy Review, 2016, 24(3), 100–107. [4] MacAlister, A. Virginia Tech, 2013.