Injuries are produced by the rapid decrease in velocity over a short distance (deceleration). Severity of injury depends on energy transferred during deceleration as a result of a crash.

Unlike MVCs, the driver or passenger usually absorbs all the impact and the associated kinetic energy.

The majority (75%) of motorcycle deaths are from head injury.

Spine, pelvis, and extremity injuries are also common, with pelvic fractures particularly severe and life-threatening.

There is a high risk of limb loss with open or severe injury to the tibia and fibula.

Although pedestrian–automobile impacts account for only 2% of traffic injuries, they account for 13% of traffic-related deaths. Children, the elderly, and the intoxicated are more at risk for this mechanism of injury. The pattern of injury is depicted in Figure 22-2. Torso trauma (chest, abdomen, and pelvis) represents 6% of the injuries; however, musculoskeletal and intra-abdominal are more common (35% and 27%, respectively).

This type of impact often results in Waddle’s triad of injury: (1) Tibiofibular or femur fracture, (2) truncal injury, and (3) craniofacial injury. Therefore, a patient with two components of Waddle’s triad of injury should be assumed to have the third component as well.

In general, small children tend to be “run over” and adults “run under” or thrown over the car with impact onto the street.

A lateral compression pelvic fracture can occur as a result of contact between the hip and the fender of the motor vehicle.

Falls in the elderly, including ground level falls, are the leading cause of unintentional injury fatality in the United States, having recently surpassed MVC for this distinction. Anticoagulation medications and other comorbidities contribute.

Injuries sustained in falls depend on distance of fall, surface struck, and the position on impact.

Energy at impact is the product of the patient’s weight times distance of fall times gravitational forces.

Falls of 2 to 3 times the height of the patient are associated with more injury: >20 ft in adults and >10 ft in children. Three story falls have a mortality of 50%. Survival is rare in free falls from above five stories.

Injury patterns differ depending on how the patient lands. If the patient lands on his or her feet from a height above 10 to 15 ft, the injuries may include calcaneal, lower extremity, pelvis, and spine fractures. Thoracic aorta and renal injuries can also occur.

Falls with a horizontal orientation result in greater energy dissipation and fewer injuries. This is a less predictable injury pattern and includes craniofacial trauma, hand and wrist fractures, along with abdominal and thoracic visceral injuries.

Young males are the most commonly injured by this mechanism, with injury patterns being variable (depending on the weapon, position of the person being assaulted, and the magnitude and intensity of the attack).

Head and facial injuries are more common (72%).

Defensive posturing of the patient usually results in lower extremity injuries (10%).

Severe torso injuries (including pancreatic and hollow viscus injuries) can occur from a stomping or kicking injury.

An intoxicated assault patient with a depressed level of consciousness has an intracranial injury until proven otherwise.

To understand the mechanisms of gunshot injuries, it is important to understand the nature of firearms and their projectiles. Ballistics is defined as the scientific study of projectile motion and is divided into three categories: Internal, external, and terminal ballistics. Internal ballistics has to do with the projectile within the firearm. External ballistics describes the projectile in the air. Terminal ballistics relates to actions of the projectile in its target. Wound ballistics is a subset of terminal ballistics; it is the most important aspect of ballistics for physicians to understand. However, to completely understand the wounding process some knowledge of all aspects of ballistics is necessary.