Patterns of Blunt Injury

Mechanism of Injury

Trauma is a physical injury with associated dissipation of energy to and within the person involved. Trauma can occur as a result of a blunt, penetrating, or thermal mechanism. The actual mechanism of injury often dictates the specific management approach. In addition to the mechanism, patterns of injury are important. Specific injuries can be anticipated based on some patterns of injury. Also, possible associated injuries must be considered for every diagnosed injury (Tables 2-1 and 2-2).

TABLE 2-1 Blunt Trauma: Documented and Possible Associated Injuries

Documented injury Possible associated injuries Neck injury (±cervical fracture) Carotid artery injury Sternal or first/second rib fracture Thoracic aortic injury, myocardial contusion, atrial rupture Scapula fracture Pulmonary contusion, thoracic aortic injury Chest wall injury (rib fractures 6–12) Left side—splenic injury, right side—hepatic injury Lumbar fracture (L2-L5) Pancreatic contusion/transection, intestinal rupture Abdominal wall abrasion/ contusion (“seatbelt” sign) Intestinal rupture, mesenteric rent Severe pelvic fracture Bladder rupture, urethral transection, rectal/vaginal injury Shoulder dislocation (anterior) Axillary nerve injury Knee dislocation (posterior), supracondylar femur fracture Popliteal artery injury (intimal tear/thrombosis) Bilateral calcaneal fractures Lower extremity and vertebral fractures, renal/thoracic aortic injuries

TABLE 2-2 Penetrating Trauma: Documented and Possible Associated Injuries

Documented injury Possible associated injuries Cervical (platysma penetration) injuries Jugular vein/carotid artery injury, tracheal/ esophageal injury Transmediastinal injury Cardiac/tracheobronchial and pulmonary/vascular/ diaphragmatic/gastrointestinal injury Thoracoabdominal injury Pulmonary/diaphragmatic/cardiac/gastrointestinal injury Transabdominal injury Gastrointestinal/hepatic/vascular injury Transpelvic injury Bladder/intestinal/uterine/vascular injury Flank injury Genitourinary/intestinal injury

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Blunt Trauma

I. Types

• Motor vehicle crashes
• Motorcycle crashes
• Pedestrian-automobile impacts
• Falls
• Assaults

II. Motor Vehicle Crashes (MVCS)

• 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.
  • MVCs account for over half of the deaths from unintentional causes.
  • MVCs cause at least half of closed head and spinal cord injuries.
  • The risk of a major injury increases 300% to 500% if the victim is ejected (including a 1 in 13 risk of spinal column injury).
  • MVCs involve three types of collisions:
    • Primary collision—motor vehicle impacts another object
    • Secondary collision—victim strikes internal components of the car
    • Deceleration-induced deformation—results in differential movement of fixed and nonfixed anatomic parts (e.g., shearing injury to the brain or transection of the thoracic aorta)
• Determinants of injury
  • Magnitude of force (force = mass × acceleration)
  • Location of victim (front seat versus back seat; driver versus passenger)
  • Restraint devices (Table 2-3)
    • Injury risk is greatest in the unrestrained victims.
    • Lap belts alone decrease mortality by 50% (there is, however, an increased rate of abdominal injury).
    • The lap belt is designed to fit across the pelvis (the anterior superior iliac spines). If inappropriately worn over the abdomen, compression fractures of the lumbar spine (Chance fractures) can occur. Lap belt injuries are associated with small bowel and colon injuries. Such injuries also include mesenteric tears and thrombosis of the abdominal aorta.
    • Three-point constraints plus airbags provide the optimal protection, especially in front-end collisions.
    • Secondary collisions of occupant with the vehicle are reduced with the utilization of three-point restraints. Ejection is prevented and mortality is substantially decreased.
    • With three-point constraints, extremity injuries are not prevented. Also, there is no effect on major injury patterns with side impact collisions.
    • Shoulder belt should not be worn without the lap component; the driver and passengers can slip under this restraint.
    • Shoulder belt injuries are associated with multiple vascular injuries, including intimal damage or thrombosis of innominate, subclavian, carotid, or vertebral arteries.

      TABLE 2-3 Restraint Devices
      Lap belt Shoulder belt Shoulder and lap belts Airbags (frontal and side impact)

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      • Airbags allow a less traumatic deceleration when compared to three-point restraints. The proportion and severity of lower extremity injuries are increased relative to torso and head injuries. However, airbags can cause injuries to occupants who are facing backward or leaning against the steering wheel or into another passenger's compartment.
  • Unrestrained (driver and front seat occupants)
    • The majority of injuries in frontal crashes are a result of impact with the steering wheel, windshield, dashboard, or floorboards. These injuries include the following:
      • cranial injuries (16%)
      • facial fractures (37%)
      • cervical spine injuries (10–15%)
      • major thoracic injuries (46%)
      • abdominal injuries (5–10%)
      • femur fractures (65%)
      • distal lower extremity fractures (33%)
      • forearm fractures (46%)
    • Lateral crashes (“T-bone”)
      • A lateral crash can result in direct impact between the vehicle and the occupant because of the limited space between the driver and the colliding vehicle.
      • Because there is very little substantive material to blunt such an impact, lateral impact collisions are associated with twice the mortality of frontal impacts.
      • Thoracic and abdominal injuries are most prevalent.
      • The occupant is projected into the next compartment.
    • Rear-end impact collisions
      • Rear-end impact collisions do not usually cause severe injuries, with only 8% of crashes resulting in serious injury.
      • An extension flexion injury (“whiplash”) is common.
    • Rollover collisions
      • Because of the random nature of these collisions, force vectors vary.
      • Kinetic energy of the car is usually dissipated over a long distance.
      • Roof collapse can produce severe head injury.
      • Axial load forces can result in compression fractures of the spine.
      • Ejection of the occupant can occur.
    Unrestrained (backseat passenger)
    • The rear seat passengers have the same risk of injury as those in the front seat except the direct injuries sustained from the steering wheel and dashboard impact.
    • Rear seat passengers are less likely to be restrained.
    • Unrestrained rear seat passengers can be a projectile, potentially causing injury to both themselves and occupants in the front seat.

III. Motorcycle Crashes

• Unlike motor vehicle crashes, the driver or passenger usually absorbs all the impact and the associated kinetic energy.
• The majority (75%) of motorcycle deaths are a result of cranial injuries.
• Spine, pelvis, and extremity injuries are also common.
• Less obvious fractures can occur.
• There is a high risk of limb loss with open or severe injuries to the tibia and fibula.

IV. Pedestrian-Automobile Impacts

• 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 Fig. 2-1. Torso trauma (chest, abdomen, and pelvis) represents 6% of the injuries; however, musculoskeletal and intraabdominal are more common (35% and 27%, respectively).
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  Figure 2-1. Pedestrian-automobile impact. (©Baylor College of Medicine 1986. Modified from Feliciano DV, Moore EE, Mattox KL, eds. Trauma. 3rd ed. Norwalk, Conn: Appleton and Lange, Englewood Cliffs, NJ; 1996:97, with permission.)

• 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.

V. Falls

• Injuries sustained in falls depend on distance of fall, surface struck, and the position on impact.
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• Energy at impact is the product of the victim's weight times distance of fall times gravitational forces.
  • Kinetic energy is dissipated, on impact, throughout the skeleton and soft tissues.
  • Duration of impact (i.e., how quickly the victim stops) is critical in determining injury severity.
    • Impact force over a shorter time increases the magnitude of injury.
    • Harder surfaces increase severity of injury because of immediate deceleration and transfer of all energy to the body (e.g., concrete vs. grass, sand, or snow).
• Fall injuries are frequent in the elderly. Comorbidities are major determinants of outcome and can also contribute to causing the fall.
• Femoral neck fractures and head and cervical spine injuries can result from the elderly falling while walking.
• Falls occurring from a height can involve a tumbling mechanism or a “free fall.” Free falls imply a fall from a height directly to the ground.
• Falls of 25 to 30 feet (three stories) have a mortality of 50%. Survival is rare in free falls from above five stories.
• Injury patterns differ depending on how the victim lands. If the victim lands on his or her feet, from a height above 10 to 15 feet, the pattern of injuries could 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.

VI. Assaults

(fisticuffs, kicking, stomping, striking with an object)

• 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 victim 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 victim with a depressed level of consciousness has an intracranial injury until proven otherwise.

Axioms

• Patterns of injury are associated with specific mechanisms.
• Severity of injury depends on the energy transferred to the injured person.
• Lateral impact collisions cause twice the mortality as compared to frontal crashes.
• Falls of 25 to 30 feet (three stories) have a mortality of 50%.