Aorta can be injured in variety of accidents or trauma. A piercing or penetrating injury by a sharp object can directly injure the aorta in the thorax or abdomen. These injuries are often instantly fatal due to severe bleeding.
More commonly aorta is injured in blunt trauma especially in high velocity deceleration accidents. Typically the person is thrown from a speeding bike and comes crashing. The relatively fixed part of aorta (close to the position of ligamentum arteriosum) takes the brunt of impact.
So commonest site of injury in these injuries is opposite the left subclavian artery. Aorta may be sustain partial tear of intima and/or media or a complete tear. The complete tear is a devastating injury accounting for heavy mortality- 20% of victims die before reaching medical facility. Untreated another 10% die every hour following injury. Needless to say, this is a true surgical emergency.
Sometimes the extensive traumatic dissection can cause malperfusion of the visceral vessels or intercostals. Bleeding into the chest can severe enough to cause hypotension and shock.