Advanced Trauma Life Support ATLS Student Course Manual 2018

BIOMECHANICS OF INJURY
Injuries occur when energy that is greater than
tissue tolerances is transmitted to the human
body. Transmitted energy can be kinetic, thermal,
chemical, radiant, and electrical. Biomechanics (“bio”
meaning life, and “mechanics” meaning motion and
forces) is the science of the internal and external forces
acting on the human body and the effects produced
by these forces. Biomechanics plays an important
role in injury mechanisms, especially in motor
vehicle crashes.
Impact biomechanics includes four principal
areas of study: (1) understanding the mechanism of
injury; (2) establishing levels of human tolerance
to impact; (3) defining the mechanical response to
injury; (4) and designing more biofidelic crash test
dummies and other surrogates. Details of the injury
event can yield clues to identifying 90% of a patient’s
injuries. Specific information for doctors to elicit
regarding the biomechanics and mechanism of
injury includes
••
The type of traumatic event (e.g., vehicular
collision, fall, or penetrating injury)
••
An estimate of the amount of energy
exchanged (e.g., vehicle speed at impact,
distance of the fall, and caliber and type
of weapon)
••
The collision or impact of the patient with
the object (e.g., car, tree, knife, baseball bat,
or bullet)
Mechanisms of injury can be classified as blunt,
penetrating, thermal, and blast. In all cases, energy is
transferred to tissue—or, in the case of freezing, energy
(heat) is transferred from tissue. The following are
select laws of mechanics and conservation of energy
that help us understand how tissues sustain injury.
1. Energy is neither created nor destroyed; however,
its form can be changed.
2. A body in motion or a body at rest tends to remain
in that state until acted on by an outside force.
3. For every action there is an equal and opposite
reaction.
4. Kinetic energy (KE) is equal to the mass (m) of the
object in motion multiplied by the square of the
velocity (v) and divided by two. Therefore, even
a modest increase in velocity can dramatically
increase kinetic energy.
5. Force (F) is equal to the mass times acceleration
(or deceleration): F = ma.
6. Injury is dependent on the amount and speed of
energy transmission, the surface area over which
the energy is applied, and the elastic properties of
the tissues to which the energy transfer is applied.
7. The size, shape (e.g., sharp, blunt, or jagged), and
mass of the impactor modify the amount of energy
transmitted to the tissues.
Common injury patterns and types of injuries identified
with blunt trauma include
••
Vehicular impact when the patient is the
occupant of the vehicle
••
Pedestrian
••
Injury to cyclists
••
Assaults (intentional injury)
••
Falls
••
Blast injury
Vehicular Impact
KE = (m)(v)
2
Blunt Trauma
Vehicular collisions can be subdivided further into
(1) collision between the patient and the vehicle’s
occupant compartment, or between the patient
and an object outside the vehicle if the patient is
ejected (e.g., tree or ground); and (2) the collision
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