Blunt abdominal trauma (BAT) comprises 75% of all blunt trauma and is the most common example of this injury. The majority occurs in motor vehicle accidents, in which rapid deceleration may propel the driver into the steering wheel, dashboard, or seatbelt causing contusions in less serious cases, or rupture of internal organs from briefly increased intraluminal pressure in the more serious, dependent on the force applied. It is important to note that initially there may be little in the way of overt clinical signs to indicate that serious internal abdominal injury has occurred, making assessment more challenging and requiring a high degree of clinical suspicion.
There are two basic physical mechanisms at play with the potential of injury to intra-abdominal organs: compression and deceleration. The former occurs from a direct blow, such as a punch, or compression against a non-yielding object such as a seat belt or steering column. This force may deform a hollow organ thereby increasing its intra-luminal or internal pressure, leading to rupture. Deceleration, on the other hand, causes stretching and shearing at the points at which mobile structures, such as the bowel, are anchored. This can cause tearing of the mesentery of the bowel, and injury to the blood vessels that travel within the mesentery. Classic examples of these mechanisms are a hepatic tear along the ligamentum teres and injuries to the renal arteries.
When blunt abdominal trauma is complicated by 'internal injury', the liver and spleen (see blunt splenic trauma) are most frequently involved, followed by the small intestine.
In rare cases, this injury has been attributed to medical techniques such as the Heimlich Maneuver, attempts at cardiopulmonary resuscitation and manual thrusts to clear an airway. Although these are rare examples, it has been suggested that they are caused by applying unnecessary pressure when administering such techniques. Finally, the occurrence of splenic rupture with mild blunt abdominal trama in those convalescing from infectious mononucleosis is well reported.