If an adult is struck by a truck with a high front, the situation is the same as with a child. With non-braking or late-braking, the impact to the adult is above the center of gravity and the individual is slammed down and run over. If the truck is braking hard prior to impact, the individual is thrown forward.
If adults are struck by an automobile or light truck, rather than a truck with a high front, a different pattern of injuries occurs because victims are impacted below the center of gravity. With non-braking or late-braking automobiles at very high speed, the pedestrian is picked up and thrown over the top of the car. Examination of the automobile reveals either scuff marks or dents on the bumper, as well as denting of the front of the hood in most instances. There may be dents on the roof or trunk of the car, when the individual is hurled over it. The authors have seen this pattern in individuals struck at high speeds, i.e., the high 60s and 70s mph range. In these cases, there is often mangling of the body with partial or complete amputation of a limb by the massive blunt trauma (Figure 9.15). The skin in the groin area may show traumatic striae (stretch marks) if it has been violently stretched by impact at the buttocks (Figure 9.16). Striae might also be present on the neck because of violent bending with subsequent massive fracture of the cervical vertebrae.
If the motor vehicle is traveling at a moderate speed at the time of impact, the pedestrian will be picked up, land on the hood, and slide backward, then impacting the windshield and sliding off. The automobile will then present
Figure 9.17 Typical pattern of damage to motor vehicle that has impacted a pedestrian. Dented hood and impact site on windshield.
the classic picture of a pedestrian impact: scuffing or dents on the bumper, indentation of the front and top of the hood, and an impact site on the windshield (Figure 9.17). Fragments of glass from the windshield may be found in the hair of the victim, because often it is the head that hits the windshield. In addition, hair might be found in the windshield. The authors have also seen the weave pattern of clothing imprinted on the hood. In some instances, threads have been caught by the deformed hood, which could be linked to clothing. As the body impacts the front of the hood and indents its top, paint smears can be imparted to the clothing. All of the aforementioned trace evidence can be used to link a victim and car in cases of hit and run.
If the pedestrian is struck by the extreme lateral or outer portions of the front of the vehicle, i.e., the headlight area, the individual will be picked up onto the fender and will roll off. Damage to the car will generally be confined to the headlight area and the fender, with no damage to the top of the hood or the windshield.
If an automobile traveling at either high or moderate speed brakes hard prior to impact with an adult, there are two possibilities, in both of which the pedestrian is struck below the center of mass by a rapidly decelerating vehicle. In the first possibility, the pedestrian is thrown forward. In the second, the individual is struck by the vehicle, picked up, lands on the hood, and is then propelled forward, again coming to rest in front of the rapidly decelerating vehicle. In the latter case, there will be damage to the front and top of the hood.
The first portion of a motor vehicle to impact a pedestrian is the bumper. If the automobile is not braking, in most present-day vehicles the impact point in a male of average height would be the knee region or just below it. Obviously, with shorter individuals, it will be higher. Most drivers, however, are able to brake prior to hitting a pedestrian. Because of this, the bumper impacts the mid or lower aspect of the tibia and fibula, that is, the calf region. Depending on the speed of the vehicle and the strength of the bones, there might be fractures of either or both the tibia and fibula, with the fractures either closed or open. These are called "bumper fractures" (Figure 9.18). Not uncommonly, bumper fractures are at different levels
on the two legs. This suggests that the individual was either walking or running at the time of impact, with the higher-placed injury indicating the leg that was in contact with the ground and supporting the body weight. If the individual was oriented sideways to the impacting vehicle, the "bumper fractures" might be confined to one leg. In some instances, there are no fractures, just abrasions of the skin and hemorrhage into the calves. In other cases, there might be no visible injuries and it is not until an incision is made in the calf that one sees internal hemorrhage. Occasionally, no injury is present. The long-bones fractures produced by impaction with the bumper are usually of two types — first, a wedge-shaped fracture with the apex of the wedge pointing in the direction of the force, and, second, an oblique fracture.20
On impact, the pedestrian is picked up with the head and trunk impacting the hood and windshield. Often, the body pivots on impact such that the buttocks and upper thigh region strike the front of the hood. The tangential force directed by the hood to the buttock and thigh may cause stripping of the skin and subcutaneous tissue from the muscles, creating a pocket in the upper thigh-buttock region. There can be extensive bleeding into these pockets, with collection of 1-2 L of blood. These pockets are often not visible externally. They can be readily palpated and then exposed with an incision (see Figure 5.8).
As the individual is picked up and thrown by the vehicle, he can literally be stripped of his clothing. The authors have seen cases in which bodies have been found on a highway dressed only in a shirt and undershorts. At first, it was thought that the individuals were intoxicated and were walking around half dressed. Subsequent examination at the scene revealed their trousers, often turned inside out, with paint smears on the outer surface. In other words, these individuals were struck by the motor vehicle and, as they were thrown through the air, the trousers and shoes were stripped from the body. Horizontal linear marks on the ankles may represent the edges of shoes that were torn off the feet.
If an individual is run over by a wheel, there are often tire tread marks on one surface of the body with scrape-like abrasions on the opposite side, i.e., the pavement side (Figure 9.19). The abrasions are caused by the body's scraping along the ground as the spinning tire pushes it backward. Tire tread marks are not invariably present, but if they are, may be on the clothing as well as, or instead of, the skin (Figure 9.20). If the wheel passes over a limb, the spinning movement of the tire may avulse skin and subcutaneous tissue from the fascia and muscle (Figure 9.21).
In hit-and-run deaths, photographs of the tread marks with a ruler in the field should be taken for subsequent comparison with a tire. In passing over a victim, grease or dirt from the undersurface of the car can be deposited
on the body or clothing. Head hair, samples of grease from the body, and the clothing should be retained. When a suspect vehicle is found, the under-surface should be examined for blood, hair, and clothing fibers. Any material recovered can then be compared with material removed from the body.
In pedestrian accidents, the most common causes of death are head injuries and fracture-dislocations of the cervical spine, predominantly at the atlanto-occipital joint. In many pedestrian accidents, injuries to the chest and abdomen are minimal or absent. The determining factor as to amount of injury appears to be the velocity of the vehicle and whether the individual was thrown into a fixed object. There are usually abrasions and lacerations of the face where the head has impacted the ground after the body is thrown. Extensive scrape-like abrasions may be present on the body where it has skidded across the pavement. If the individual was fully dressed in heavy material, there might be virtually no injuries on the outside of the body, except for some minor abrasions of the face and head.
Just as thoracic aorta lacerations occur in drivers and passengers, so can they also occur in pedestrians struck by a vehicle. Brundage et al. reported a 12.7% incidence of traumatic rupture of the thoracic aorta in a review of 220 pedestrian fatalities.21 The predominant site of laceration was immediately distal to the origin of the left subclavian artery (15 of 28 cases, or 53.6%). Four (14.3%) were in the ascending aorta or arch of the aorta. In half the individuals with aortic injury, there was associated thoracic spinal injury.
Occasionally, an individual will be found on a road or a parking lot with crushing injuries of the body, tire tread marks on one surface, and brush abrasions on the opposite side (Figure 9.22). No evidence of an impact with the front of a motor vehicle will be seen. Toxicology virtually always will show acute alcohol intoxication. These are individuals who have gone to sleep or passed out on a road or in a parking lot, only to be subsequently run over by a vehicle whose driver did not see them.
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