Describe the injuries in road traffic accidents in pedestrians and vehicle occupants.

Pedestrian Injuries

Primary impact — the first contact of the vehicle with the body. The bumper injury is the key finding: a bruise, abrasion or laceration with an underlying fracture of the tibia and fibula. Its height above the heel is measured and recorded, since it indicates the type of vehicle and whether it was braking at impact — braking dips the front and lowers the point of contact → secondary impact — the body is thrown onto the bonnet and windscreen, producing head, chest and upper limb injuries; a patterned imprint of the radiator grille, headlamp or wiper may be left → secondary injuries — the body falls to the road, producing graze abrasions and head injury, often on the opposite side → run-over (crush) injuries — the wheel passes over the body, producing tyre-tread patterned abrasions and bruises (highly identifying), avulsion and "flaying" or degloving of the skin by the shearing rotational force, crushing of the chest with multiple rib fractures, and rupture of internal organs → dragging — extensive parallel graze abrasions over a wide area, with road grit ground into the wounds

• The measured height of the bumper injury is the single most useful measurement; it distinguishes a car from a truck or bus, and a lowered bumper height indicates braking, both of which bear directly on the reconstruction
• Injuries are characteristically on the opposite side to the primary impact as well, from the fall, and this distribution is typical of a pedestrian rather than an occupant

Occupant and Motorcyclist Injuries

Medicolegal Aspects and Applied Aspects

• The questions to be answered — was the person a pedestrian, driver or passenger? Was the death due to the accident or to natural disease causing it? Was alcohol or a drug involved? Was the person alive at the time, or was a body run over to disguise a homicide? Which vehicle was responsible? And was there any survival period?
• Always preserve blood for alcohol and drugs in both drivers and pedestrians, using sodium fluoride with potassium oxalate, which prevents both fermentation and glycolysis; and note that alcohol may be generated after death by putrefaction, so a fluoride-preserved sample and vitreous humour together are far more defensible
• Consider natural disease as the cause of the accident — myocardial infarction, epilepsy, stroke or hypoglycaemia in the driver; this changes the case entirely and is found only if the heart and brain are examined properly
• Examine and preserve the clothing and footwear; paint, glass and rubber traces link the body to a particular vehicle, and the sole of the shoe may show the characteristic scuff of a pedestrian being struck
• Measure the bumper injury height from the heel, and record it; it is the single measurement most often needed by the investigator and most often omitted
• Look for the seat-belt mark on every occupant, and photograph it; it establishes the seating position objectively
• Distinguish antemortem from postmortem run-over injuries; a body placed on a road and run over to simulate an accident shows no vital reaction in the crush injuries, while the true cause of death lies elsewhere
• Tyre-tread patterned bruising identifies the vehicle and should be photographed with a scale before anything else is done to the body
• Whiplash can kill with almost no external injury; a rear-end collision death with an unremarkable body requires careful examination of the cervical cord and brain stem
• A helmet properly worn transforms the outcome for a motorcyclist, and its presence, type and whether it was fastened should be recorded as part of the examination
• Take vitreous humour as well as fluoride blood for alcohol; postmortem alcohol production is a standard defence argument and the paired samples answer it
• Injuries on the side opposite the impact are typical of a pedestrian, from the fall to the road, and help distinguish a pedestrian from an occupant