Trauma mechanisms

The following information is taken from: Varon, Albert J. (2012-06-01). Essentials of Trauma Anesthesia. Cambridge University Press. Kindle Edition.

Transfer of energy occurs due to blunt and penetrating trauma according to Sir Isaac Newton’s first law of motion, which states that “a body in motion will stay in motion unless acted upon by an outside force.”

Severity of injury is related to three factors:

1. Kinetic energy absorbed by the body (KE = mass × velocity2/2)
2. Direction the energy travels through the body.
3. Body structure density: solid (water dense) organs are more likely to rupture than hollow (air dense) organs. Bone and cartilage are more rigid and have greater density.

Falls account for the largest number of non-fatal injuries.

Characteristics of the contact surface, position of the person upon landing, and change in velocity determine the injury severity.

1. Landing on feet: full force is transmitted up the axial skeleton with injuries to the calcaneus, tibia, femoral neck, and spine. Intra-abdominal organs may be avulsed off their mesenteries or peritoneal attachments.
2. Landing on back: energy is transferred over a larger area.
3. Landing on head: severe head injury and cervical spine fractures.

Motor vehicle collisions are the leading cause of trauma deaths and years of life lost for every age from 5 through 34 in the United States.

The type of impact is associated with characteristic patterns of injury.

1. Frontal down and under: fracture dislocations of the ankle, tibia, knee; fractures of the femur and acetabulum.
2. Frontal up and over: rib fractures, sternal fracture, blunt cardiac injury (contusion, valve disruption, rupture), pulmonary trauma, cervical spine fracture, facial fractures, head injury, abdominal trauma.
3. Lateral: injury of clavicle, ribs, lung, pelvis, and spleen. Other injuries may occur: femur fracture, aortic tear.
4. Rear: whiplash injuries.
5. Sideswipe/rotational: combination of injury patterns as in frontal and lateral impacts.
6. Rollover: complicated spectrum of injuries depending on forces, restraints, roof deformation, and ejection.
7. Ejection: may result in severe crush or total amputations. Increased risk of death. Ejection of the passenger is considered to have the greatest injury potential, as just about any type of injury can result, due to the multitude of forces involved in this injury pattern.
8. Seatbelt and air bag: restraint devices protect against head, face, chest, abdominal, and extremity trauma. The lap belt when worn above the iliac crest can result in hyperflexion of the torso over the seatbelt with anterior compression fracture of the lumbar spine (Chance fracture). A shoulder restraint may cause trauma to the clavicle. Deployment of the airbag can cause corneal, facial, and neck trauma.

Cyclists collisions: The potential for injury is high, because there is very little protection for the passenger. A massive amount of energy is transferred to the cyclist on impact. The main piece of equipment that offers protection is a helmet.

1. Frontal, ejection: any part of the head, chest, or abdomen can hit the handlebars. Blunt abdominal injuries and femur fractures may occur.
2. Lateral or ejection: open or closed extremity fractures occur on the impacted side. Secondary injury occurs upon landing.
3. Laying down the bike: increases the stopping distance for kinetic energy to dissipate. Soft tissue injuries and road burn on the down limb. Injury severity decreased by wearing protective gear.
4. Helmets: these are designed to reduce direct force to the head and disperse it over the entire foam padding of the helmet. There is no doubt that helmets reduce the risk of fatal head injury after motorcycle and bicycle collisions.

Pedestrian injuries: Often affect children, the elderly, and intoxicated persons. The pattern of injury depends on the height of the patient and the type of vehicle.

1. Bumper: tibia-fibula fractures, knee dislocations, and pelvic injuries.
2. Hood and windshield: truncal injuries such as rib fractures or splenic trauma. If the victim is thrown into the air, other organ compression injuries may occur.
3. Ground: this occurs when the patient slides off the car and hits the ground and may result in head and face injuries as well as extremity fractures.

Penetrating trauma. Gun-related deaths are the second leading injury-related fatality in the United States, second only to motor vehicle collisions.

In 2007, there were 17,352 suicides and 12,632 homicides due to firearms in the US. There were 30,335 violence-related firearm deaths and 54,165 violence-related non-fatal injuries, a mortality rate of 35.9%.

The problem of homicide due to guns is particularly acute in the young, inner-city, African-American male population. Homicide due to firearms is the second-leading cause of death, in those aged 10–24. The firearm death rate has steadily increased over the past few decades, due almost exclusively to the homicide rate in the adolescent and young adult population.

Determinants of tissue damage from a bullet are:

1. Amount of energy transferred to the tissues.
2. Time it takes for the transfer to occur.
3. Surface area over which the energy is transferred.
4. Velocity of the bullet (kinetic energy).
5. Wound ballistics like cavitation, trajectory, yaw, tumbling, and fragmentation.
6. Entry and exit wounds. These are critical determinants of trajectory and path of the missile. The trajectory may not be linear if the bullet ricochets off bony structures.

Stab wounds Damage by sharp, cutting edges. Surrounding damage is minimal, and there is no blast effect as seen in gunshot wounds. Mortality, while still present, is generally much lower. In 2007, 2,600 patients died due to violence-related cutting and piercing deaths in the United States. In the same year, a total of 175,482 non-fatal such injuries occurred. The mortality rate due to this mechanism is 1.5%.

Blasts or explosions: Cause injury in three distinct manners:

1. Primary: direct effect of high-pressure waves on the tympanic membrane, lung (pulmonary edema, hemorrhage, bullae, or rupture), and bowel. Intraocular hemorrhage and retinal detachment may occur.
2. 2. Secondary: objects rendered mobile by the explosion may cause penetrating and/or blunt trauma.
3. 3. Tertiary: the patient may become mobile from the blast and injuries may be similar to those sustained from a fall or ejection.