Football Helmet (system) to Reduce Subdural Hemorrhaging by Mitigating Rotational Acceleration

1. Doug Browne Jeff Markle Tyler Severance Football Helmet (system) to Reduce Subdural Hemorrhaging by Mitigating Rotational Acceleration

2. What Causes Subdural Hemorrhage? • Subdural hemorrhaging occurs when the blood vessels that connect the dura to the brain rupture • This can happen when the brain moves relative to the dura, causing the connecting vessels to stretch and burst • Due to a higher density of CSF relative to brain tissue density (4% greater) • How much strain would be significant?

3. Rotational Acceleration • From cadaveric studies at Vanderbilt University, the connecting blood vessels undergo permanent deformation at 120% strain and total rupture at 150% strain which occurs at accelerations between 4,500 and 10,000 rad/s2

4. Rotational Acceleration Dangers in American Football • Well verified that collisions in football can exceed dangerous levels of rotational acceleration • In all levels of football (high school, college and professional) the top 1% of collisions far exceed critical levels of rotational acceleration • Collisions cannot be prevented without drastic change in the sport; however, helmet design can be modified to protect against the potential risk

5. Force and Effects

6. Collisions in General • Conservation of Energy: • Energy is neither created nor destroyed. • Collisions in American football are inelastic collisions; kinetic energy is not conserved. • In an example where two players strike each other and fall to the ground, the kinetic energies of both players immediately prior to the collision are converted to deformational energy as the respective velocities of both players rapidly decrease to 0. • Energy attenuating properties of helmets (and shoulder pads) decrease the amount of deformational energy that is transmitted to vital structures.

7. Breaking down a collision • Striking player comes from the left and drives through defender • First response is helmet compression • Force from Internal liners cause head to move about y-axis • Impact only lasts about 15 msec in total • Highest strains here occur in the midbrain several msec after impact forces have peaked http://www.youtube.com/watch?v=k1nXnX1sKIo

9. Helmeted Collisions • It is interesting to note the incidence of brain injuries actually peaked many years after the introduction of helmets. • Helmet use became mandatory in the NCAA in 1939 and the NFL in 1940. These rule changes, and the addition of the facemask in the 1950s, afforded increased protection to the head but also led to unanticipated changes in behavior and/or technique—with initial contact now more frequently being made with the helmet. • Consequently, the incidence of brain-injury related fatalities peaked during the 5-year span from 1965 to 1969. • In response, the National Operating Committee on Standards for Athletic Equipment (NOCSAE) was founded in 1969 and the first safety standards for helmets were implemented in 1973.

10. NOCSAE • The National Operating Committee on Standards for Athletic Equipment is the governing body that regulates standards for football helmets. • Helmets are only required to prevent against levels of translational acceleration • Strong emphasis placed on the drop test • This is flawed • Only been proven to correlate with skull fractures • The demand to raise the threshold score of the test (to make it more applicable to concussions) has been discouraged due to “technological limitations and sacrifices to the sport”

11. Current Helmet Design Problems • Visited Southern Impact Research Center (one of the limited locations certified to test helmets) to meet with Dave Halstead, one of the nation’s leading experts on helmet design • Additionally, Halstead explained and showed that concussions can occur without contact to the head • Current helmets are effective at dampening blows to the head (difficult to improve upon), but this is a different issue than lowering overall angular acceleration

12. First Steps • After meeting with Halstead, we identified several main issues our team could “tackle” • Helmet weight • Detection of dangerous accelerations • Large range of un-resisted motion • Lightweight helmet that keeps similar levels of protection against linear acceleration as current models • Include in the helmet a device that indicates when dangerous levels of rotational acceleration have been reached. • Attempt to add increasing resistance to range of motion to prevent the head from reaching the peak levels during the collision

13. New possibilities • Spring coiled safety door closers use a dashpot to reduce acceleration when closing • Example of controlled angular deceleration • As angle inc, angular resistance inc • Viscoelastic based properties • One drawback -> one dimensional • Might be possible to use network of these (shoulder pad = origin; helmet = insertion) to restrict quick movements but not inhibit deliberate ones

14. Prototype • Spring loaded design • Incorporate the padding system of a butterfly collar • Used in 3 different directions of support • Helmet would rest in between the padding network • Focused in y axis with minimal emphasis on x and z • Allow movement, inhibit rapid acceleration • *** Helmet and Shoulder pads are a separate network… still are easy to remove and separate

15. Complete design as of 3/22

16. Obstacles • Only potential drawback is the creation of a spring loaded design • Spring rotators have a dashpot sense in that they offer a constant internal resistance • Internal resistance reduces the peak acceleration/deceleration and this is where the design is successful

17. Steps to come • Testing at Southern Impact • Hope to utilize high velocity projectile test to better simulate multiple directional force • Also plan to use drop test but only to compare our model to existing ones • Further testing and modification can occur as needed for the rest of the semester

18. References • 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. • LöwenhielmP: Strain tolerance of the vv. cerebri sup. (BVs) calculated from head-on collision tests with cadavers. Z Rechtsmedizin75:131–144, 1974. • GennarelliTA, Thibault LE: Biomechanics of acute subdural hematoma. J Trauma 22:680–686, 1982. • Lee MC, Ueno K, Melvin JW: Finite element analysis of traumatic subdural hematoma, in Proceedings of the 31st Stapp Car Crash Conference. New York, NY, Society of Automotive Engineers, 1987, pp 67-77.

19. References Con’t • 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. • Forbes JA, Withrow TJ: Biomechanics of Subdural Hemorrhage in American Football. Vanderbilt University, 2010

20. Final Note: • To learn more about Southern Impact Research Center, please visit: • http://www.youtube.com/watch?v=hwA-hiFu4Xw • http://www.soimpact.com/