Aetiology

Understanding the mechanism of the abdominal trauma is important in acquiring a sense of the severity of the injury and in beginning to build a differential diagnosis of potential injuries. Mechanisms associated with a large amount of energy transfer, such as high-speed motor vehicle accidents, have a greater chance of causing more harm than lower-speed accidents. The aetiology of traumatic abdominal injuries falls into two broad categories: blunt and penetrating abdominal trauma.

Blunt abdominal trauma

Blunt abdominal trauma is caused by two types of forces: shear strain and tensile strain.

  • Shear injuries occur at a point of attachment of an organ during abrupt acceleration or deceleration. For example, during rapid deceleration, the liver may continue to travel relative to the ligamentum teres, causing shear forces around this point of attachment leading to liver laceration. The kidneys, spleen, large bowel, and small bowel are also vulnerable to injuries related to shear forces.

  • Tensile injuries are those related to direct compression or stretching of tissue. The liver, spleen, and pancreas are usually injured during frontal impact, while the kidney is affected when there is direct impact to the flank. Direct compression of the abdomen is also associated with an increase in abdominal pressure that potentially results in pelvic fractures or a ruptured diaphragm.

Penetrating abdominal trauma

As a foreign object passes through a body part it decelerates, thus transferring energy to the neighbouring tissue. The amount of tissue damage is related to the velocity and size of the foreign body. High-velocity gunshot wounds create more tissue damage surrounding the trajectory of the bullet than those of low velocity.

Penetrating abdominal trauma involves a smaller area of tissue than blunt abdominal trauma. The organs injured by penetrating abdominal trauma depend on the path taken by the foreign body as it passes through the body. It is important to understand that the path of a bullet is unpredictable, due to its tendency to ricochet off bones. The trajectory can also be misleading, due to changes in body positions from the time of injury to the time of examination. Bullets can also fragment upon hitting bones, thus creating multiple unexpected injuries.

Penetrating injuries create cavitations along their path and can carry foreign material (i.e., clothing) with them. These cavitations carry the risk of becoming infected days after the injury.

Stomach, small bowel, and colorectal injuries occur more frequently following penetrating abdominal trauma than following blunt trauma. The small bowel is the organ most commonly injured by penetrating abdominal trauma.

There is a high incidence of diaphragmatic injury in thoraco-abdominal penetrating trauma.[12]

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