Football Helmet (system) to Reduce Subdural Hemorrhaging by Mitigating Rotational AccelerationDoug BrowneJeff MarkleTyler Severance

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?

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

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

Level Measurement StudyTranslational Acceleration

(g)

Rotational Acceleration (rad/s^2 )

High School Top 1% of Impacts Schnebel et al., 2007 114.5g NA

CollegeTop 1% of Impacts Schnebel et al.,

2007 127.8g NA

Average Impact Duma et al., 2005 32g 2,213

ProfessionalAverage Concussion Pellman et. al, part

II 97.8g 6,432Average Concussion

+ 1 standard deviation

Pellman et. al, part II 125.5g 8,245

Force and Effects

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.

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

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.

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”

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

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

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

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

Complete design as of 3/22

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

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

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.

Löwenhielm P: Strain tolerance of the vv. cerebri sup. (BVs) calculated from head-on collision tests with cadavers. Z Rechtsmedizin 75:131–144, 1974.

Gennarelli TA, 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.

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

Final Note:

To learn more about Southern Impact Research Center, please visit: http://

www.youtube.com/watch?v=hwA-hiFu4Xw

http://www.soimpact.com/