D. M. Browne 1 , J. H. Markle 2 , T. S. Severance 2 , J. Forbes MD 3

1. Designing a Football Helmet System to Reduce Subdural Hemorrhaging by Mitigating Rotational Acceleration D. M. Browne1, J. H. Markle2, T. S. Severance2, J. Forbes MD3 Mechanical Engineering, Vanderbilt University, Nashville, TN 37235 2. Biomedical Engineering, Vanderbilt University, Nashville, TN 37235 3. Department of Neurosurgery, Vanderbilt Medical Center, Nashville, TN 37235 Methodology Results Abstract Recently, American Football has garnered significant publicity regarding increased frequency of traumatic head injuries. Designers race to engineer helmets to further reduce translational accelerationand yield better results for the standardized drop test – used to evaluate effectiveness of helmets. Unfortunately, new trends in helmet design fail to mitigate angular acceleration, which is proven to cause strain in the blood vessels connected to the brain. Relative strain between the brain and the connecting dura matter leads to vessel deformation and rupture causing catastrophic brain injuries such as subdural hemorrhages (SH). Football collisions provide sufficient rotational force to cause the rupture of these vessels. To address these issues, our team designed a helmet-shoulder pad system that mitigates this angular acceleration and brings it down to safer levels. It provides a continuous and variable force to the back of the helmet (without being directly connected) which allows for a normal range of motion, but when subjected to extreme forces, prevents dangerous levels of rotational acceleration. This reduces the peak acceleration levels and minimizes the movement discrepancy between the brain and the duramatter reducing risk of injury. • After the construct was completed, the resistive force was measured at given angles • Three trials were performed at each of three significant angles and the means were calculated • Figure 2 shows the effects of angular displacement on the resultant force • The measured force was tangential to the path of rotation, and thus, needed to be converted into angular resistance • Design consists of three coil springs with rotating arms attached to a modified butterfly collar • Arms provide force to the helmet, increasing the effective mass of a player’s head • Larger effective mass makes head harder to move and thereby decreases rotational acceleration • Utilizing springs, force applied increases as the head moves back • The harder a player gets hit, the more the device will resist the motion • At “resting” position, minimal force is applied. • Permits normal movement of a player during normal game play Figure 2: Measured tangential force over the range of motion of the damper system (1) (2) (3) (4) (5) Background and Goals Conclusion and Suggestions • National Operating Committee on Standards for Athletic Equipment (NOCSAE) is responsible for all helmet regulation • Helmets are tested only for their ability to limit translational forces and accelerations. • Measured through a drop test originally designed to prevent skull fracture. • There is currently no regulation for the level of rotational acceleration allowable by helmets despite studies showing that they can directly lead to subdural hemorrhages (SH). • Construct provides a reduction in the peak rotational acceleration • Could result in fewer traumatic brain injuries and improve overall safety • Elimination of the forward force on the head at rest is necessary before marketing can be considered • Forward force could result in neck misalignment and a high-risk position for spinal injuries • An improved setup would include • An accelerometer to indicate when the athlete has undergone a severe collision and needs medical attention • An indicator to inform the user when the protective lining is no longer functional or in a state of post-compression • This could help avoid situations where injuries go undetected and lead to significant complications • Design yielded promising results in the reduction of rotational accelerations and could be improved to a marketable model with more available resources • The graphs in Figure 4 show the effects of increasing velocities of a tackling player on the peak angular acceleration reached during a collision • The blue lines in Figure 4 A and B show the accelerations of unmitigated collisions without any form of added protection • The green lines in Figure 4 A and B show the new acceleration values when the designed shoulder pad system is applied • The red lines represent the acceleration threshold of SH found through studies of cadaveric tissue as seen in Table 1 • These simulations were performed in MATLAB using the results garnered from testing trials (Figure 2) • When performing the calculations, it was necessary to apply certain worst case assumptions which maximized peak accelerations • These simulations offer a hypothesis for future testing at NOCSAE certified labs to further validate the effectiveness of the system • SHs occur when the brain moves relative to the skull, causing the connecting blood vessels to stretch to rupture. • Studies also show that collisions in football may lead to rotational acceleration levels sufficient to cause subdural hemorrhaging (Table 1). • Project Goal: To develop a system that would lower the levels of rotational acceleration on the head during a collision. References Figure 3: Side view (left) and top view (above) of the construct • Forbes JA, Withrow TJ: Biomechanics of Subdural Hemorrhage in American Football. Vanderbilt University, 2010 • Huang HM, Lee MC, Chiu WT, Chen CT, Lee SY: Three-dimensional finite element analysis for subdural hematoma. J Trauma 47: 538–544, 1999. • Depreitere B, Van Lierde C, Vander Sloten J, Van Audekercke R, Van Der Perre G, Plets C et al.: Mechanics of acute subdural hematomas resulting from BV rupture. Journal of Neurosurgery. 104(6): 950-956, 2006. • Löwenhielm P: Strain tolerance of the vv. cerebri sup. (BVs) calculated from head-on collision tests with cadavers. Z Rechtsmedizin75:131–144, 1974. • Gennarelli TA, Thibault LE: Biomechanics of acute subdural hematoma. J Trauma 22:680–686, 1982. • Lee MC, Haut RC: Insensitivity of tensile failure properties of human BVs to strain rate: implication in biomechanics of subdural hematoma. J Biomech 22(6-7): 537-42, 1989. A B Acknowledgements Our group would like to thank our advisor Dr. Jonathan Forbes from the Vanderbilt Department of Neurological Surgery for his generous contributions and advice on our project. In addition, we would also like to thank Dave Halstead of Southern Impact Research Center of his technical help and advice throughout the design process. His assistance was invaluable. Figure 4: Rotational acceleration measured with and without the shoulder pad construct in both collegiate (A) and professional (B) settings. Figure 1: Incoming Force, effect on rotation, and rotational strain caused