The Threelevel Injury Of The Driver

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Fig. 55. Levels of injury potentially sustained by an unrestrained driver in a frontal collision. The pathologist must be aware that even restrained occupants can be injured by intrusion into the occupant compartment. (Reprinted from ref. 489 with permission of Lippincott Williams & Wilkins.)

Fig. 56. Frontal collision; intrusion and deformation of steering wheel. (Courtesy of Road Safety and Motor Vehicle Regulation Directorate, Transport Canada.)
Fig. 57. Toe pan intrusion. Deformity of ankles owing to fracture-dislocation; laceration of left shin.

occupant must be restrained by the seat belt as early as possible during a crash. In a frontal impact, the emergency locking retractor in a seat belt system locks, and as the driver moves forward, the belt system is loaded. The lap and shoulder components of the seat belt effectively restrain the pelvic girdle and torso, respectively, from moving forward. In a seat belt system, most of the stretching occurs in the shoulder belt portion. As a result, the occupant's upper torso pivots over the lap belt. Facial and head injuries are possible, even for fully restrained occupants, in severe frontal collisions. Relative seat belt slack increases seat belt loading of the occupants. Slack allows greater excursion distances during a crash, which increases occupant contacts with the interior (503). Pyrotechnic preten-sioners in new cars eliminate seat belt slack. Load limiters, in conjunction with airbags, provide resistance but allow forward excursion to meet the deployed airbag. In rare cases of heavy loading, the belt fails, releasing the occupant (500).

The effectiveness of any restraint system in reducing serious injuries is compromised in high-severity collisions when there is intrusion into the occupant compartment (497-500,504-507).

Seat belt-associated injuries occur (Table 2).

Serious visceral injuries from seat belts are uncommon and are usually associated with the belt being worn improperly (502,503). Serious injuries are also a reflection of higher severity crashes (>48 km/h or 30 mph) and the nature of the collision (e.g., rollover increases the possibility of partial ejection and "hanging" in a restraint system [499,500,549,550]). The lap part of the belt must be worn on the bony pelvis, and the torso belt needs to be positioned across the chest (500,501,515). A lap belt worn higher on the abdomen can cause injury. Instead of loading the strong bony pelvis, the load is transmitted to the abdominal organs and the lumbar spine. Constitutional factors

Table 2

Seat Belt-Associated Internal Injuries

Lap belt-related

Abdominal wall soft tissue disruption (499,501,508-510)

• Transection of torso (511)

Diaphragm tear (secondary herniation of abdominal viscera [512]) Gastric rupture (353)

Small and large bowel trauma (contusion, seromuscular laceration, perforation, transection, secondary infarction [499,502,505,510,513-521])

• Transection of appendix (522) Omental tear (499)

Mesentery injury (contusion, laceration, internal herniation [499,501,502,508,510,515]) Pancreas (disruption, inflammation [523])

Abdominal aorta trauma (contusion, intimal tear, dissection, thrombosis, secondary embolization, acute or delayed rupture with aneurysm [293,294,301,524-530])

• Iliac artery (intimal tear [499,531]) Inferior vena cava laceration (319,532)

• Renal vein tear Kidney laceration (532)

Lumbar spine fractures (499,505,510,513,519,520,533)

Pelvic fractures (499,500)

Pregnancy-related

• Fetal demise secondary to:

° Abruptio placentae (536,538,540-542) ° Trauma (craniocerebral, other viscera [538-540,543,544]) Shoulder belt-related

Atlanto-occipital disolocation (545)

Cervical spine fractures (all levels including "hangman's" fracture [499,546-548]) Decapitation (499,548,549) Strangulation (499,550)

Larynx injury (fractures, transection [499,546,548]) Tracheal transection (548,551-553) Cervical esophagus perforation (554)

Chest wall fractures (ribs, sternum, clavicle, chondrosternal dislocation [499,502,555])

Thoracic spine fractures (546,547,556,557)

Thoracic aorta trauma (laceration, transection [275,502,556])

Major arteries:

° Carotid artery (transection, dissection [530,546,551,558,559]) ° Vertebral artery injury (560) ° Subclavian artery (intimal tear [555,560]) ° Innominate artery rupture (561) Heart (contusion, laceration [502,562,563]) Lung (contusion, laceration [502]) Pleura, pericardium (laceration [502]) Liver (laceration [502,555])

• Avulsion of hepatic veins (499) Spleen (laceration [395,499,502])

Kidney (laceration including renal artery and vein [499])

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