UNDERSTANDING HEAD AND NECK TRAUMA

(Or, why helmets increase the danger!)

 

 

HEAD AND NECK TRAUMA

Trauma is a type of injury  which  effects the body by external  force being  applied  in a  violent  and  sudden  manner.  When  dealing  with motorcycle  accidents,  it’s important to understand the types of forces which a rider is subjected to, the body parts  affected by these forces, and how the body reacts to certain inertia or ‘g-forces’.

It has been suggested by NHTSA that helmets might prevent neck injury.  This was  prompted  by  testimony  before the  Tennessee  Transportation Committee  when I stated that helmets could cause cervical  spine injury due to  their  weight.  In order  to rebut  these  remarks,  a  regional spokesman  for NHTSA  testified  that more  people  receive  neck injury without a helmet than those  wearing  helmets.  Therefore, he concluded, without any foundation or  authorities,  that helmets might prevent neck injury.  This of course is utter nonsense.

First, let’s define the different types of trauma.

1.                Penetrating trauma

2.                Blunt trauma

3.                Acceleration/deceleration trauma

 

Penetrating  trauma is an object  entering  the body or head due to an object  striking  the  body, or the body  being  placed  in  motion  and striking an object which then penetrates the body.

Blunt trauma occurs when an object strikes the body or head with force causing a compression of body tissues which results in injury.

Acceleration/deceleration  trauma  occurs  when the body is moving and strikes  another moving or stationary  object.  This results in a change of motion  for the body, or a  complete  stop of  motion,  which  causes stretching and tearing of body tissues.

When  considering  the way the FMVSS 218 standard  tests helmets, it’s clear that these  tests in no way  simulate an actual  crash  situation.  The headform in the helmet has no neck or neck sensors and the helmet is stationary with a weight dropped on it (compression)  from an elevation.

To  properly  simulate a crash, a full form  human  crash  test  dummy should be used (or perhaps the regional  spokesman  for NHTSA),  whereby the dummy is moving at a certain  speed and then comes to an abrupt halt or strikes a stationary object (acceleration/deceleration).

‘G-Forces’

‘G-forces’  are what  determines  the  extent of injury to the head or neck  in many  motorcycle  accidents.  When a body  is  stopped  (due to crashing into a stationary  object) or is hurled into space with a three pound helmet  flexing the neck, the force of gravity  causes the body to weigh many times its actual  weight.  For  example,  a male human  head, without  helmet, weighs about 10 pounds.  If subjected to 10 ‘G’s’, that head briefly weighs about 100 pounds,  passing that stress and load onto the neck.  Consider adding a 3 pound helmet, and you begin to appreciate the forces your neck has to contend with.

Going a little  further, using a full form human dummy,  developers of the Head and Neck  Support  (HANS)  device  found that the head  briefly experiences  25 ‘G’s’ and weighs about 250 pounds in a 35  mile-per-hour impact.  With those  forces in play, the  delicate  human brain  bounces around  in side  the  skull  (coup/contrecoup)  with a  force  equal  to weighing  75 pounds.  A normal  brain  weighs  about 3 pounds.  Combined with this is the fact that the  rotation of the head and neck during one of these crashes  causes severe tearing and stretching of the tissues of the brain and brain stem.  No helmet can prevent this  collision  of the brain within the skull.

It has been  suggested  that  race car  drivers  exceed  speeds of 200 miles-per-hour  and walk away from crashes because they had a helmet on.  Again, this is a half-truth, manipulated statement by pro-helmet forces.  the truth is race cars are no  longer  built  out of  strong,  resilient materials.  Modern technicians have learned that in order to protect the driver, the race car must crush and  disintegrate  during a crash.  This allows for a more gradual,  extended  period to distribute  the force of the  crash  and  decelerate  the  ‘G’s’.  With  a  deformable  structure construction,  akin to airplane  design, the chassis and body of the car takes up most of the ‘G’ forces,  according to Rick Amabile in his book, Inside Indy Car Racing:  1990.  Besides the chassis design, the internal cockpit of the cars is better designed also.  Direct blows to the driver are  minimized  through  a  safety  system  integrating  a  seat  angled backwards at 45 degrees and a six-point safety harness system.  The weak link in this equation, again, is the neck.

The neck was listed on 31.5 percent of incident reports in races.  The Sports Car Club of America (SCCA) performed some analyses on their races and found 17 percent of the injuries sustained were neck injuries.  This led to the  development of the HANS device, which  supports the head and neck, helping prevent whiplash and rotational injuries.  This device was developed by Biomechanical  Design Inc., of East Lansing, Michigan.  The importance  of  this  type of  device  becomes  very  evident  when  one considers  that  according  to one of the  nations  largest  insurers of motorsports  events, North American Racing Insurance  (NARI), 93 percent of all driver injuries were caused by direct blows or sudden,  twisting, deceleration forces applied to the body.

The mere fact that a racer is wearing a helmet has little or no impact on his  survivability  without the other safety  engineering  factors in place.  With a complete safety  engineered race car, the National Safety Council  puts  driving  one of these  units in the same hazard  range as swimming  and  alpine  skiing.  In fact,  according  to their  charts, a modern  race car driver is at less risk than a scuba  diver or  mountain climber, and much less at risk than a parachutist or hang glider.

The problem with motorcycle design is we don’t have the safety cockpit that would afford us the room and time for a  disintegrating  chassis to take up the  ‘G-forces’  for us.  And we don’t have  anything  padded in front of us to reduce the loads  reaching our neck, such as a break away steering  wheel or padded dash panel.  To say race car drivers walk away from  crashes  because  they wear  helmets is absurd.  Several  Indy car racers  recently  died of closed  skull  trauma to the brain, due to the exact   twisting   and   tearing   actions   we  said  were   caused  by acceleration/deceleration, which helmets cannot protect against.  Yet we don’t hear NHTSA explain or comment about these cases.

According to SCCA data, the neck is the most often  injured  body part (31.5  percent),  followed by the back (19.5 percent), and then the head (15.8 percent).  Severe  centrifugal  forces exert  tremendous  shearing pressures  on the brain.  This  causes the brain to impact on the inside of the skull, or tear at the medulla at the brain  stem.  Developers  of the HANS used crash test dummies in their testing  procedures  and found the head can briefly  encounter 25 ‘G’s’, amounting to about 250 pounds, in a 35 mph impact.  Gravitational  forces are dependent on speed, and a doubling of speed quadruples the ‘G-forces’.

To determine the number of ‘G-forces’ in a collision, the formula is:

G’s=.0333X(M.P.H.  X M.P.H.)  Distance.  In other words,  multiply the square of the  vehicle’s  speed, in mph, times  .0333 and divide it by the  stopping  distance  in  feet.  This  is  for a  direct,  head  on collision, and the formula is more complex in angular  collisions  due to the fact that the kinetic  energy is expanded over a longer  period of time, resulting in lower ‘G-forces’.

Collision, collision, collision.

There are actually three collisions occurring in a crash:

1.     Vehicle vs whatever it contacts with

2.     body vs whatever it contacts with

3.     body tissues and organs vs body tissues and organs

 

Once  your  vehicle  strikes  another  object,  you  have  suffered  a collision.  At that point your body is slammed into some  stationary  or moving object, or perhaps  ejected and is thrown to the ground.  At that point, your  internal  organs,  including  the brain,  began a collision course of their own.  Brain  injury can occur  without any impact to the head,  whether  helmeted  or not.  If the body  comes to a sudden  stop, including the head and skull, the brain continues to move and slams into the inner skull wall.  Brain tissue and blood  vessels can shear in this violent,  twisting  action.  The  skull,  even  without  a  helmet,  can withstand  hundreds  of ‘G’s’,  but the  brain  cannot.  Other  internal organs,   especially  the  heart  and  aorta,  are  subjected  to  these tremendous  forces,  and  often  rupture  or  tear.  To  give a  graphic example,  a 160 pound man will  strain at his seat belt with a weight of 6,400 pounds at a 40’G’  deceleration.  Now you might  understand why so many  people  die from  ruptured  or torn  aortas in  crashes.  There is basically little  connective tissue to anchor the heart, since it has to palpitate and move during its rhythmic beating.

‘G-Force’ Tolerance: Head vs Neck

It is believed that the head can  withstand 300  ‘G-forces’,  which is higher than other body parts.  The deceleration of ‘G-forces’,  movement of the head and duration of the  incident  all  determine  the amount of injury the head will  sustain.  It is common to have skull  fracture and no brain  injury, and brain  injury and no skull  fracture.  Helmets are designed to  distribute  the force of the impact over a wide  surface in order to reduce the amount of ‘G-forces’  reaching the brain.  The force of inertia in a crash can cause brain  injury even  without an impact to the head, thus a helmet cannot protect against this event.  Brain tissue and blood vessels can be torn by inertia when the head  rotates,  common occurrence amplified with helmet use.  The weight of the head and helmet pulling at the neck can be  sufficient  to fracture the skull.  Known as basal skull fracture (hangman’s noose analogy), these injuries can often be fatal.

According  to NARI, the neck is the most  often  injured  body part in their studies.  this might account for the fact that the NHTSA  regional spokesman said there are more neck injuries  without  helmets than with, thus leading him to his erroneous  conclusion that helmets might prevent neck  injury.  Tests  using  human  cadavers  found  that  the neck  can tolerate about 42 foot-pounds of backward whiplash force before injuries began to occur.  The muscles in the rear of the neck are  stronger  than those in the front, thus a forward  rotating head will allow the neck to withstand  about 140  foot-pounds  of force.  Of course, these are ideal positions,  direct  forward or backward  movement.  In a real crash, the head is  bounced  in all  sorts  of  directions,  and the  neck is  less tolerant of sideways acceleration/deceleration.  In these instances, the neck can handle about 33 foot-pounds of force.

How  strong is the  unhelmeted  head?  The  amount of force a head can withstand  depends on several  factors,  including  the  location of the impact, the size of the object  striking the head and the density of the individuals  bone tissue.  The frontal bone  (forehead) can withstand on average, 1,000 to 1,600 pounds of force.  The temporo-parietal (sides of head) bones can tolerate  around 700 to 1,900 pounds of force.  the back of the skull can handle  around 1,440 pounds of force.  The bones of the face and  cheek are less  tolerant,  standing  forces of only 280 to 520 pounds.

Remember,  the brain cannot  withstand  the same forces the skull can, and even a helmet  cannot  prevent  dangerous  forces from  reaching the brain or the brain moving within the skull cavity.

When we said that the forward  rotating head can transmit energy loads to the neck, and the neck can tolerate about 140  foot-pounds  of force?  Well, when the engineers  conducted tests on their HANS safety restraint system,  they used a full human  form crash  test  dummy.  With the HANS restraint  system in  place,  the dummy  was held in  position  during a frontal impact collision, resulting in neck loads under 130 foot-pounds.  When tested  without  the  restraint  system in place, the dummy’s  head rotated  forward in the  simulated 40 mph test  collision,  and the neck received loads of nearly 1,000 foot-pounds.  The dummy was helmeted, and I suggest that if the  spokesman for NHTSA really  believes  helmets can prevent  neck  injury, he climb onto the test sled, put on a helmet  and see how his neck handles 1,000 foot-pounds of pressure.