Transcript Final Design Poster- April 26th, 2011 - Research

Designing a Football Helmet System to Reduce Subdural
Hemorrhaging by Mitigating Rotational Acceleration
D. M.
1
Browne ,
J. H.
2
Markle ,
T. S.
2
Severance ,
J. Forbes
3
MD
1. 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
Abstract
Results
• 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
140
120
y = 14.292e0.0303x
R² = 0.9936
100
Force (N)
Recently, American Football has garnered significant publicity regarding increased
frequency of traumatic head injuries. Designers race to engineer helmets to further
reduce translational acceleration and 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 dura matter reducing risk of injury.
Methodology
80
60
40
20
0
0
20
40
60
Angle (Degrees)
80
• 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
o The harder a player gets hit, the more the device will resist the motion
• At “resting” position, minimal force is applied.
o Permits normal movement of a player during normal game play
Figure 2: Measured tangential force over
the range of motion of the damper system
𝐹𝑜𝑟𝑐𝑒:
𝑀𝑜𝑚𝑒𝑛𝑡𝑢𝑚:
𝑇𝑜𝑟𝑞𝑢𝑒:
𝐴𝑛𝑔𝑢𝑙𝑎𝑟 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦:
Level
College
Professional
Schnebel et al., 2007
Translational
Acceleration (g)
127.8g
Rotational
Acceleration (rad/s^2 )
NA
Average Impact
Duma et al., 2005
32g
2,213
Average Concussion
Average Concussion + 1
standard deviation
Pellman et. al, part II
97.8g
6,432
Pellman et. al, part II
125.5g
8,245
Measurement
Study
Top 1% of Impacts
• The graphs in Figure 4 show the effects of increasing velocities of a tackling player
on the peak angular acceleration reached during a collision
o The blue lines in Figure 4 A and B show the accelerations of unmitigated
collisions without any form of added protection
o The green lines in Figure 4 A and B show the new acceleration values when
the designed shoulder pad system is applied
o 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
A
B
8000
Collegiate Collision
Collegiate with Construct
Threshold for SH
7000
6000
5000
4000
3000
2000
1000
0
0
2
4
6
8
Velocity of tackling player (m/s)
Figure 1: Incoming Force, effect on rotation, and rotational strain caused
𝜔𝑓𝑖𝑛𝑎𝑙 ∗ 𝜔𝑖 ∗ 𝑡
(5)
• Construct provides a reduction in the peak rotational acceleration
o 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
o Forward force could result in neck misalignment and a high-risk position for
spinal injuries
• An improved setup would include
o An accelerometer to indicate when the athlete has undergone a severe
collision and needs medical attention
o An indicator to inform the user when the protective lining is no longer
functional or in a state of post-compression
o 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
Figure 3: Side view (left) and top
view (above) of the construct
Peak Angular Accel. (Rad/s2)
• 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.
𝛩=
1
2
(1)
(2)
(3)
(4)
Conclusion and Suggestions
Peak Angular Accel. (Rad/s2)
Table 1. Peak acceleration measured during football collisions for college and professional players.
𝑅
𝐴𝑛𝑔𝑢𝑙𝑎𝑟 𝐴𝑐𝑐𝑒𝑙𝑒𝑟𝑎𝑡𝑖𝑜𝑛
Background and Goals
• 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.
o 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).
𝐹 =𝑚∗𝑎
𝑚1 𝑣1 + 𝑚2 𝑣2 = 𝑚2 𝑣2 𝑓𝑖𝑛𝑎𝑙
τ=F∗d
𝑣
𝜔=
10
12
References
1.
2.
9000
8000
3.
Professional Collision
Professional with Construct
Threshold for SH
7000
4.
6000
5.
6.
5000
4000
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
Rechtsmedizin 75:131–144, 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.
3000
Acknowledgements
2000
1000
0
0
2
4
6
8
10
12
Velocity of tackling player (m/s)
Figure 4: Rotational acceleration measured with and without the shoulder pad construct in
both collegiate (A) and professional (B) settings.
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.