Trauma is a physical injury caused by transfer of energy to and within the person involved. Abdominal trauma is best categorized by mechanism as blunt and penetrating abdominal injuries. The mechanism of injury dictates the diagnostic workup. As there is a broad spectrum of abdominal injuries, abdominal trauma patients are often difficult to assess. Confounding factors, such as associated extra-abdominal injuries or altered mental status (either from a head injury or intoxication) further complicate the evaluation.  Hepatic injury is the most common intra-abdominal organ injury.
The surface anatomy of the abdomen extends from the nipple line to the groin crease anteriorly and from the tips of the scapulae to the gluteal skin crease posteriorly. The specific anatomic boundaries of the abdomen are the diaphragm, abdominal wall musculature, pelvic skeletal structures, and vertebral column. There are 3 basic regions of the abdomen: the peritoneal cavity with its intrathoracic component, the retroperitoneum, and the pelvic portion. As the diaphragm rises as high as the fourth intercostal space, trauma to the lower chest may involve abdominal organs.
Blunt abdominal trauma
Causes of blunt abdominal trauma include motor vehicle accidents (MVAs), motorcycle crashes (MCCs), pedestrian-automobile impacts, falls, and assaults. MVAs are the most common cause of blunt abdominal trauma, causing about 75% of such injuries. In the US in 2007 there were 41,059 fatalities from 37,435 fatal MVAs, 5154 fatalities related to MCCs, and 5504 pedestrians struck.  In about one third of these deaths, alcohol was involved. Prevention strategies, such as campaigns against driving while intoxicated and encouragement of seatbelt use, have been shown to be effective in decreasing blunt abdominal trauma-related morbidity and mortality.    
Blunt abdominal trauma can result in multiple different organ injuries. Complications of blunt abdominal trauma include peritonitis, hemorrhagic shock, and death. Common injuries are divided into 2 categories: solid organ (e.g., liver, spleen, pancreas, kidneys) and hollow organ (e.g., stomach, large and small bowel, gallbladder, urinary bladder) injuries. Solid organ injuries range from minor injuries such as small hemodynamically insignificant liver, spleen, or kidney lacerations to devastating injuries requiring immediate intervention. Bowel injuries require surgical repair to prevent peritonitis and septic shock.
Diaphragmatic injury accounts for <10% of blunt abdominal trauma, and splenic injury is more common with blunt than penetrating abdominal trauma.
Penetrating abdominal trauma
Penetrating abdominal injuries occur when a foreign object pierces the skin, and these may be accidental or intentional. The most common penetrating injuries are gun shot wounds (GSWs) and stab wounds. In the US, penetrating trauma remains a major cause of morbidity and mortality, with 30,143 firearm-related deaths occurring in 2005. Of these deaths, 29,354 were intentional (i.e., suicide or homicide) and 789 were accidental. In European countries, firearm-related injuries are much less common.
The external appearance of the penetrating wound does not determine the extent of internal injuries. It is important to define the trajectory of a penetrating wound and to consider all possible internal injuries. The mortality associated with penetrating abdominal trauma is related to the intra-abdominal organs injured, with refractory hemorrhagic shock being the leading cause of death. 
The small bowel is injured more with penetrating than with blunt abdominal trauma, and it is the most commonly injured organ with penetrating abdominal trauma. There is a high incidence of colorectal injury in penetrating abdominal trauma, but it is rare in blunt abdominal trauma. Stomach injuries are rare with blunt abdominal trauma, but common with penetrating abdominal trauma. Pancreatic injury is more common with penetrating than blunt abdominal trauma, and there is a high incidence of diaphragmatic injury in thoracoabdominal penetrating trauma.