EMT Exam: Differentiating Blunt from Penetrating MOI

Although you may think there are lots of MOIs (mechanism of injury), they really boil down to two general forms for the EMT exam: blunt and penetrating. Each has unique properties. In addition, you have to consider blast MOI, which is a combination of blunt and penetrating MOI.

Blunt MOI

Blunt MOI spreads its force over an area of the body. You need to think beyond the surface and predict what injuries you may find in the following situations:

  • Motor vehicle crashes: There are a few types of motor vehicle crashes (MVCs):

    • Frontal: The front of the vehicle is struck, either directly or offset. The body is flung forward, sometimes in an upward or downward motion. You expect injuries to be focused on the front of the body — the head, neck, chest, and abdomen. There may also be injuries to the arms and legs.

    • Rear: The back end of the vehicle is struck, causing the body to lurch backward first, and then whip forward. If the headrest is placed too low, the neck can hyperextend during the first reaction. Injuries to the neck, spine, and pelvis are possible during a rear collision.

    • Lateral: The side of the vehicle is struck. The body moves to the side of the impact, causing injuries to the lateral head, neck, shoulder, chest, abdomen, and pelvis.

    • Rollover: The vehicle is flipped onto its side or roof after impact. This type of accident can be especially dangerous for unrestrained passengers; they experience multiple impacts with both the inside of the vehicle and any flying objects inside the cabin during the crash, causing a multitude of injuries in a variety of places on the body.

    • Rotational: The vehicle spins after impact. The injuries can be highly variable. The initial impact can also cause injuries; for example, say two cars collide in a frontal offset crash, causing one to spin off to one side. It then crashes laterally into a building. If the occupants are not restrained, they will collide with a variety of surfaces within the vehicle, including each other.

    Restraints and other safety equipment in motor vehicles are quite good in minimizing injuries in crashes. Regardless, make sure you evaluate the MOI and assess the patient for any potential injuries associated with it.

  • Pedestrians, motorcyclists, and bicyclists, oh my! Motor vehicles can carry a lot of energy through their mass and speed. People are at a severe disadvantage during a collision when they’re on foot, a motorcycle, a bicycle, or another type of wheeled transport.

    You need to look for MOI signs of the energy involved in the collision. If the victim was thrown, estimate the distance from where the victim was struck. Damage to the motor vehicle hood, door, or bumper can provide key information. Look for tire skid marks from the motor vehicle — if they occurred before the point of impact, the energy transfer may have been less than expected.

  • Falls: Falls represent another form of blunt trauma. Acceleration is related to force, so it’s important to determine the approximate height of the fall as a predictor of serious injury. If the distance is three times the height of the patient or more, or at least 15 feet, there is great potential for serious injury.

    Knowing the suddenness of the stop on the other end of a fall is also important. Soft sand, bushes, and other materials that can slow the deceleration improve the victim’s chances of escaping serious injury.

    Finally, how the patient lands after falling can help you determine injury patterns.

  • Falling objects and assaults: Being struck by bats and falling objects are examples of blunt MOI. These MOI produce more localized injury patterns to the body. You want to identify the offending object and determine the point of impact on the body and what happened afterward.

Penetrating MOI

Penetrating MOI concentrates its force into a specific area of the body, creating an opening through the skin. Examples of penetrating MOI include

  • Gun shots: In gun shots, velocity makes all the difference. The faster the bullet, the more damage it can cause. A low-velocity projectile from a small handgun tends to cause damage along its trajectory. A high-velocity projectile from a rifle has a cavitational, or pressure, effect, causing tissue to compress and bleed as the bullet passes through.

    A bullet may also be deflected from its path in the body by harder surfaces such as bone. In this case, you may find it harder to predict the injury pattern.

  • Stabbing or cutting: You can consider a stabbing or cutting to be a very low-velocity penetrating trauma. As such, these injuries tend to be localized to the area.

More often than not, bullet and knife wounds bleed very little externally. Most of the bleeding occurs internally, where it can’t be seen or stopped.

If you can find out more specifics about the type of weapon used, such as the length of a knife blade or the caliber of a bullet, that’s great, but don’t waste time trying to track the information down.

Blast MOI

Injuries sustained from an explosion have characteristics of both blunt and penetrating MOIs. Here’s the progression:

  • Primary blast wave: When the explosion first occurs, a wall of air pressure rapidly expands outward in all directions. A victim who is close to the explosion will be struck by this pressure wave, causing blunt injuries to the inside of the body, especially to hollow organs.

  • Secondary blast wave: Immediately behind the primary wave is debris from the explosion itself. It may be the remainder of the original container, shrapnel embedded in a bomb, or glass and other materials from nearby structures. This debris strikes the victim, causing penetrating injuries.

  • Tertiary blast injuries: If the force of the explosion is great enough, victims can be thrown to the ground or into other solid objects, causing additional blunt and/or penetrating injuries.

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