Blunt Trauma: Mechanisms of Injury
Many first aid manuals lay out a plan of action with regards to prehospital care for the injured. These books have the information you need to get a victim to the next highest medical resource. The question stands, however: What if there is no higher medical resource than the average citizen?
With an adjustment in mindset and a commitment to acquire knowledge, equipment, and training, the average citizen can adapt standard emergency care to fit situations where stabilization and transport to a modern facility is not an option. Today, we’ll discuss some basics you should know about blunt trauma.
Blunt trauma is damage caused to the body by a blunt object, such as a club or baseball bat. Blunt trauma can cause bruising, scrapes, fractures, or organ ruptures. It can, in some circumstances, break the skin although a projectile that enters the body and stays there or passes through is considered “penetrating trauma”.
How does blunt trauma cause injury? According to the excellent textbook “Trauma” by Mattox, Moore, and Feliciano: The strain on an area due to trauma is related to the amount of deformation caused, factored with the amount (length) of tissue involved.
Types of Strain in Blunt Trauma
Let’s put “Strain” in four categories: Tensile strain, Shear strain, Compressive strain, and Overpressure.
Tensile Strain: Tensile strain occurs as opposing forces are applied to the same point, something like pulling apart a wishbone at Thanksgiving or, perhaps, a tug of war.
Shear Strain: Shear strain also involves two forces applied to a structure, but not at the same point. Think of a circus strong man tearing apart a telephone book.
Compressive Strain: Compressive strain is directly related to the deformation of an area of impact, similar to what would happen if I struck you in the ribs with a baseball bat or the jack collapsed while you were working under your car.
Overpressure: Overpressure is not unlike compressive strain, but applied to a fluid or gas-filled organ, crushing and, perhaps, rupturing it. An example might be sitting down abruptly on a balloon.
Blunt Trauma Effect on Tissue and Organs
How well the body handles a particular strain differs dependent on the type of force and the tissue being stressed. The denser the tissue, the less elastic it is. As such, more of the energy is transferred to the tissue, causing more damage. Let’s take the example of two organs: lungs and liver.
Lungs aren’t dense organs; they’re relatively elastic. Therefore, lower velocity blunt trauma tends to be dissipated across the entire organ. This leads to less damage than a similar impact would cause to a denser solid organ like the liver. Even in penetrating trauma, the shock wave due to temporary cavitation (below) causes a great deal more damage to a solid organ than one that is less dense or even hollow. Even the permanent cavity left by, say, a bullet, causes more injury to denser tissue.
To learn more about permanent and temporary cavitation in ballistic trauma, click below:
Motor Vehicle Accidents
The most common causes of serious blunt trauma are motor vehicle accidents (MVAs) or falls from a significant height. In both these situations, large areas of the body are subjected to varying amounts of trauma. In car crashes, head-on collisions are most associated with death (60%) compared to, say, side-impact (20-35%) or rear end collisions (3-5%). Rollovers are associated with a lower death rate (8-15%) than you might expect due to the fact that forces generated in the passenger compartment are randomly scattered to different parts of the car as it rolls. If the victim is somehow ejected from the vehicle, though, severity of injury and death rates are high, as the victim is traveling at the velocity of the vehicle and will likely strike an immobile object (like the ground).
Pedestrians hit by a car will have the knee as a first point of impact because the bumper is at about that level. As the (fractured and dislocated) lower extremities are pushed forward, the trunk and head are pushed forcefully down on the hood, causing fractured ribs, ruptured spleens, and head injuries. If struck by a truck or bus, the chest or abdomen will more likely be the recipient of the original impact.
Falls From Height
You might be surprised to find that patients presenting with injuries in free falls fell from an average height of just under 20 feet. Fractures account for three-quarters of injuries with 19-22% affecting the spine. Intra-abdominal injuries usually affect the solid organs like the liver, with hollow organs like bowel or bladder perforated in less than 1% of cases.
Blunt trauma can hide major injuries that can be life-threatening. In future articles, we’ll discuss blunt trauma in more detail and how best to recognize these injuries. Plus, we’ll explore what can (and cannot) be done to treat them in off-grid settings.
Joe Alton MD
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